try khash out for mapping mog_devids

There are no apparent benefits at the moment, but theoretically
it can reduce the amount of allocations we do and improve locality.

7 files changed, 695 insertions, 49 deletions

diff --git a/Makefile.am b/Makefile.am
index 0d1f29a..d0b9480 100644
--- a/Makefile.am
+++ b/Makefile.am
@@ -31,6 +31,7 @@ mog_src += compat_memstream.h
 mog_src += compat_sendfile.h
 mog_src += defaults.h
 mog_src += dev.c
+mog_src += dev.h
 mog_src += digest.c
 mog_src += digest.h
 mog_src += exit.c
@@ -93,6 +94,7 @@ mog_src += trywrite.c
 mog_src += util.h
 mog_src += upgrade.c
 mog_src += yield.c
+mog_src += klib/khash.h
 
 noinst_LIBRARIES = libnostd.a libccan.a
 LDADD = $(LIBINTL) $(top_builddir)/lib/libgnu.a \
diff --git a/cmogstored.h b/cmogstored.h
index 1381f4f..3e03fce 100644
--- a/cmogstored.h
+++ b/cmogstored.h
@@ -72,6 +72,21 @@
 #include "mnt.h"
 #include "packaddr.h"
 
+/* khash */
+#define kcalloc(N,Z) xcalloc(N,Z)
+#define kmalloc(Z) xmalloc(Z)
+#define krealloc(P,Z) xrealloc(P,Z)
+#define kfree(P) free(P)
+#include "klib/khash.h"
+
+/* TODO: send to klib upstream if it's good */
+#define mog_kh_foreach_key(h, kvar, code) do { khint_t __i;                \
+        for (__i = kh_begin(h); __i != kh_end(h); ++__i) {                \
+                if (!kh_exist(h,__i)) continue;                                \
+                (kvar) = kh_key(h,__i);                                        \
+                code;                                                        \
+        } } while (0)
+
 #define MOG_WR_ERROR ((void *)-1)
 #define MOG_IOSTAT (MAP_FAILED)
 #define MOG_FD_MAX (INT_MAX-1)
@@ -152,6 +167,7 @@ struct mog_mgmt {
 
 struct mog_queue;
 struct mog_svc;
+__KHASH_TYPE(by_mog_devid, struct mog_dev *, char);
 struct mog_svc {
         int docroot_fd;
         const char *docroot;
@@ -164,7 +180,7 @@ struct mog_svc {
         /* private */
         DIR *dir;
         pthread_mutex_t by_mog_devid_lock;
-        Hash_table *by_mog_devid;
+        khash_t(by_mog_devid) *by_mog_devid;
         Hash_table *by_st_dev;
         pthread_mutex_t devstats_lock;
         struct mog_queue *queue;
@@ -376,9 +392,7 @@ bool mog_svc_atfork_child(void *svc_ptr, void *parent);
 /* dev.c */
 struct mog_dev *mog_dev_for(struct mog_svc *, uint32_t mog_devid, bool update);
 int mog_dev_mkusage(const struct mog_dev *, struct mog_svc *);
-size_t mog_dev_hash(const void *, size_t tablesize);
-bool mog_dev_cmp(const void *a, const void *b);
-void mog_dev_free(void *devptr);
+void mog_dev_free(struct mog_dev *);
 bool mog_dev_user_rescale_i(void *devp, void *svcp);
 bool mog_dev_requeue_prepare(void *devp, void *ign);
 
diff --git a/dev.c b/dev.c
index dd46fe5..15f651a 100644
--- a/dev.c
+++ b/dev.c
@@ -3,6 +3,7 @@
  * License: GPLv3 or later (see COPYING for details)
  */
 #include "cmogstored.h"
+#include "dev.h"
 
 static int stat_prefix(struct mog_svc *svc, struct stat *sb, uint32_t mog_devid)
 {
@@ -37,20 +38,23 @@ static struct mog_dev *mog_dev_new(struct mog_svc *svc, uint32_t mog_devid)
         return dev;
 }
 
+/* lookup or create mog_dev for a given mog_devid */
 struct mog_dev *
 mog_dev_for(struct mog_svc *svc, uint32_t mog_devid, bool update)
 {
         struct mog_dev finder;
         struct mog_dev *ret;
         bool need_refresh = false;
+        khint_t k;
 
         finder.devid = mog_devid;
 
         CHECK(int, 0, pthread_mutex_lock(&svc->by_mog_devid_lock));
-        ret = hash_lookup(svc->by_mog_devid, &finder);
-        if (ret) {
+        k = kh_get(by_mog_devid, svc->by_mog_devid, &finder);
+        if (k != kh_end(svc->by_mog_devid)) { /* found */
                 struct stat sb;
 
+                ret = kh_key(svc->by_mog_devid, k);
                 if (!update)
                         goto out;
 
@@ -65,16 +69,20 @@ mog_dev_for(struct mog_svc *svc, uint32_t mog_devid, bool update)
                 /* st_dev may change due to remount, update if needed */
                 ret->st_dev = sb.st_dev;
         } else { /* create a new dev */
+                int rc;
+
                 ret = mog_dev_new(svc, mog_devid);
 
                 if (!ret)
                         goto out; /* could not stat */
 
-                switch (hash_insert_if_absent(svc->by_mog_devid, ret, NULL)) {
+                kh_put(by_mog_devid, svc->by_mog_devid, ret, &rc);
+                switch (rc) {
                 case 0:
                         assert(0 && "mog_dev existed while adding");
                         abort();
-                case 1:
+                case 1: /* never-used bucket */
+                case 2: /* deleted bucket */
                         if (!update)
                                 need_refresh = true;
                         break; /* OK, inserted */
@@ -91,22 +99,6 @@ out:
         return ret;
 }
 
-
-size_t mog_dev_hash(const void *x, size_t tablesize)
-{
-        const struct mog_dev *dev = x;
-
-        return dev->devid % tablesize;
-}
-
-bool mog_dev_cmp(const void *a, const void *b)
-{
-        const struct mog_dev *dev_a = a;
-        const struct mog_dev *dev_b = b;
-
-        return dev_a->devid == dev_b->devid;
-}
-
 static int
 emit_usage(
 const struct mog_dev *dev, struct mog_svc *svc, int fd, struct statvfs *v)
@@ -237,10 +229,8 @@ out:
         return errno ? -1 : 0;
 }
 
-void mog_dev_free(void *ptr)
+void mog_dev_free(struct mog_dev *dev)
 {
-        struct mog_dev *dev = ptr;
-
         mog_ioq_destroy(&dev->fsckq);
         mog_ioq_destroy(&dev->ioq);
         free(dev);
diff --git a/dev.h b/dev.h
new file mode 100644
index 0000000..130fde7
--- /dev/null
+++ b/dev.h
@@ -0,0 +1,12 @@
+static inline khint_t mog_dev_hash(const struct mog_dev *dev)
+{
+        return (khint_t)dev->devid;
+}
+
+static inline int mog_dev_eq(const struct mog_dev *a, const struct mog_dev *b)
+{
+        return a->devid == b->devid;
+}
+
+__KHASH_IMPL(by_mog_devid, static inline, struct mog_dev *, char, 0,
+        mog_dev_hash, mog_dev_eq);
diff --git a/klib/khash.h b/klib/khash.h
new file mode 100644
index 0000000..2d910de
--- /dev/null
+++ b/klib/khash.h
@@ -0,0 +1,617 @@
+/* The MIT License
+
+   Copyright (c) 2008, 2009, 2011 by Attractive Chaos <attractor@live.co.uk>
+
+   Permission is hereby granted, free of charge, to any person obtaining
+   a copy of this software and associated documentation files (the
+   "Software"), to deal in the Software without restriction, including
+   without limitation the rights to use, copy, modify, merge, publish,
+   distribute, sublicense, and/or sell copies of the Software, and to
+   permit persons to whom the Software is furnished to do so, subject to
+   the following conditions:
+
+   The above copyright notice and this permission notice shall be
+   included in all copies or substantial portions of the Software.
+
+   THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+   EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+   MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+   NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
+   BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
+   ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
+   CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+   SOFTWARE.
+*/
+
+/*
+  An example:
+
+#include "khash.h"
+KHASH_MAP_INIT_INT(32, char)
+int main() {
+        int ret, is_missing;
+        khiter_t k;
+        khash_t(32) *h = kh_init(32);
+        k = kh_put(32, h, 5, &ret);
+        kh_value(h, k) = 10;
+        k = kh_get(32, h, 10);
+        is_missing = (k == kh_end(h));
+        k = kh_get(32, h, 5);
+        kh_del(32, h, k);
+        for (k = kh_begin(h); k != kh_end(h); ++k)
+                if (kh_exist(h, k)) kh_value(h, k) = 1;
+        kh_destroy(32, h);
+        return 0;
+}
+*/
+
+/*
+  2013-05-02 (0.2.8):
+
+        * Use quadratic probing. When the capacity is power of 2, stepping function
+          i*(i+1)/2 guarantees to traverse each bucket. It is better than double
+          hashing on cache performance and is more robust than linear probing.
+
+          In theory, double hashing should be more robust than quadratic probing.
+          However, my implementation is probably not for large hash tables, because
+          the second hash function is closely tied to the first hash function,
+          which reduce the effectiveness of double hashing.
+
+        Reference: http://research.cs.vt.edu/AVresearch/hashing/quadratic.php
+
+  2011-12-29 (0.2.7):
+
+    * Minor code clean up; no actual effect.
+
+  2011-09-16 (0.2.6):
+
+        * The capacity is a power of 2. This seems to dramatically improve the
+          speed for simple keys. Thank Zilong Tan for the suggestion. Reference:
+
+           - http://code.google.com/p/ulib/
+           - http://nothings.org/computer/judy/
+
+        * Allow to optionally use linear probing which usually has better
+          performance for random input. Double hashing is still the default as it
+          is more robust to certain non-random input.
+
+        * Added Wang's integer hash function (not used by default). This hash
+          function is more robust to certain non-random input.
+
+  2011-02-14 (0.2.5):
+
+    * Allow to declare global functions.
+
+  2009-09-26 (0.2.4):
+
+    * Improve portability
+
+  2008-09-19 (0.2.3):
+
+        * Corrected the example
+        * Improved interfaces
+
+  2008-09-11 (0.2.2):
+
+        * Improved speed a little in kh_put()
+
+  2008-09-10 (0.2.1):
+
+        * Added kh_clear()
+        * Fixed a compiling error
+
+  2008-09-02 (0.2.0):
+
+        * Changed to token concatenation which increases flexibility.
+
+  2008-08-31 (0.1.2):
+
+        * Fixed a bug in kh_get(), which has not been tested previously.
+
+  2008-08-31 (0.1.1):
+
+        * Added destructor
+*/
+
+
+#ifndef __AC_KHASH_H
+#define __AC_KHASH_H
+
+/*!
+  @header
+
+  Generic hash table library.
+ */
+
+#define AC_VERSION_KHASH_H "0.2.8"
+
+#include <stdlib.h>
+#include <string.h>
+#include <limits.h>
+
+/* compiler specific configuration */
+
+#if UINT_MAX == 0xffffffffu
+typedef unsigned int khint32_t;
+#elif ULONG_MAX == 0xffffffffu
+typedef unsigned long khint32_t;
+#endif
+
+#if ULONG_MAX == ULLONG_MAX
+typedef unsigned long khint64_t;
+#else
+typedef unsigned long long khint64_t;
+#endif
+
+#ifdef _MSC_VER
+#define kh_inline __inline
+#else
+#define kh_inline inline
+#endif
+
+typedef khint32_t khint_t;
+typedef khint_t khiter_t;
+
+#define __ac_isempty(flag, i) ((flag[i>>4]>>((i&0xfU)<<1))&2)
+#define __ac_isdel(flag, i) ((flag[i>>4]>>((i&0xfU)<<1))&1)
+#define __ac_iseither(flag, i) ((flag[i>>4]>>((i&0xfU)<<1))&3)
+#define __ac_set_isdel_false(flag, i) (flag[i>>4]&=~(1ul<<((i&0xfU)<<1)))
+#define __ac_set_isempty_false(flag, i) (flag[i>>4]&=~(2ul<<((i&0xfU)<<1)))
+#define __ac_set_isboth_false(flag, i) (flag[i>>4]&=~(3ul<<((i&0xfU)<<1)))
+#define __ac_set_isdel_true(flag, i) (flag[i>>4]|=1ul<<((i&0xfU)<<1))
+
+#define __ac_fsize(m) ((m) < 16? 1 : (m)>>4)
+
+#ifndef kroundup32
+#define kroundup32(x) (--(x), (x)|=(x)>>1, (x)|=(x)>>2, (x)|=(x)>>4, (x)|=(x)>>8, (x)|=(x)>>16, ++(x))
+#endif
+
+#ifndef kcalloc
+#define kcalloc(N,Z) calloc(N,Z)
+#endif
+#ifndef kmalloc
+#define kmalloc(Z) malloc(Z)
+#endif
+#ifndef krealloc
+#define krealloc(P,Z) realloc(P,Z)
+#endif
+#ifndef kfree
+#define kfree(P) free(P)
+#endif
+
+static const double __ac_HASH_UPPER = 0.77;
+
+#define __KHASH_TYPE(name, khkey_t, khval_t) \
+        typedef struct { \
+                khint_t n_buckets, size, n_occupied, upper_bound; \
+                khint32_t *flags; \
+                khkey_t *keys; \
+                khval_t *vals; \
+        } kh_##name##_t;
+
+#define __KHASH_PROTOTYPES(name, khkey_t, khval_t)                                                 \
+        extern kh_##name##_t *kh_init_##name(void);                                                        \
+        extern void kh_destroy_##name(kh_##name##_t *h);                                        \
+        extern void kh_clear_##name(kh_##name##_t *h);                                                \
+        extern khint_t kh_get_##name(const kh_##name##_t *h, khkey_t key);         \
+        extern int kh_resize_##name(kh_##name##_t *h, khint_t new_n_buckets); \
+        extern khint_t kh_put_##name(kh_##name##_t *h, khkey_t key, int *ret); \
+        extern void kh_del_##name(kh_##name##_t *h, khint_t x);
+
+#define __KHASH_IMPL(name, SCOPE, khkey_t, khval_t, kh_is_map, __hash_func, __hash_equal) \
+        SCOPE kh_##name##_t *kh_init_##name(void) {                                                        \
+                return (kh_##name##_t*)kcalloc(1, sizeof(kh_##name##_t));                \
+        }                                                                                                                                        \
+        SCOPE void kh_destroy_##name(kh_##name##_t *h)                                                \
+        {                                                                                                                                        \
+                if (h) {                                                                                                                \
+                        kfree((void *)h->keys); kfree(h->flags);                                        \
+                        kfree((void *)h->vals);                                                                                \
+                        kfree(h);                                                                                                        \
+                }                                                                                                                                \
+        }                                                                                                                                        \
+        SCOPE void kh_clear_##name(kh_##name##_t *h)                                                \
+        {                                                                                                                                        \
+                if (h && h->flags) {                                                                                        \
+                        memset(h->flags, 0xaa, __ac_fsize(h->n_buckets) * sizeof(khint32_t)); \
+                        h->size = h->n_occupied = 0;                                                                \
+                }                                                                                                                                \
+        }                                                                                                                                        \
+        SCOPE khint_t kh_get_##name(const kh_##name##_t *h, khkey_t key)         \
+        {                                                                                                                                        \
+                if (h->n_buckets) {                                                                                                \
+                        khint_t k, i, last, mask, step = 0; \
+                        mask = h->n_buckets - 1;                                                                        \
+                        k = __hash_func(key); i = k & mask;                                                        \
+                        last = i; \
+                        while (!__ac_isempty(h->flags, i) && (__ac_isdel(h->flags, i) || !__hash_equal(h->keys[i], key))) { \
+                                i = (i + (++step)) & mask; \
+                                if (i == last) return h->n_buckets;                                                \
+                        }                                                                                                                        \
+                        return __ac_iseither(h->flags, i)? h->n_buckets : i;                \
+                } else return 0;                                                                                                \
+        }                                                                                                                                        \
+        SCOPE int kh_resize_##name(kh_##name##_t *h, khint_t new_n_buckets) \
+        { /* This function uses 0.25*n_buckets bytes of working space instead of [sizeof(key_t+val_t)+.25]*n_buckets. */ \
+                khint32_t *new_flags = 0;                                                                                \
+                khint_t j = 1;                                                                                                        \
+                {                                                                                                                                \
+                        kroundup32(new_n_buckets);                                                                         \
+                        if (new_n_buckets < 4) new_n_buckets = 4;                                        \
+                        if (h->size >= (khint_t)(new_n_buckets * __ac_HASH_UPPER + 0.5)) j = 0;        /* requested size is too small */ \
+                        else { /* hash table size to be changed (shrink or expand); rehash */ \
+                                new_flags = (khint32_t*)kmalloc(__ac_fsize(new_n_buckets) * sizeof(khint32_t));        \
+                                if (!new_flags) return -1;                                                                \
+                                memset(new_flags, 0xaa, __ac_fsize(new_n_buckets) * sizeof(khint32_t)); \
+                                if (h->n_buckets < new_n_buckets) {        /* expand */                \
+                                        khkey_t *new_keys = (khkey_t*)krealloc((void *)h->keys, new_n_buckets * sizeof(khkey_t)); \
+                                        if (!new_keys) return -1;                                                        \
+                                        h->keys = new_keys;                                                                        \
+                                        if (kh_is_map) {                                                                        \
+                                                khval_t *new_vals = (khval_t*)krealloc((void *)h->vals, new_n_buckets * sizeof(khval_t)); \
+                                                if (!new_vals) return -1;                                                \
+                                                h->vals = new_vals;                                                                \
+                                        }                                                                                                        \
+                                } /* otherwise shrink */                                                                \
+                        }                                                                                                                        \
+                }                                                                                                                                \
+                if (j) { /* rehashing is needed */                                                                \
+                        for (j = 0; j != h->n_buckets; ++j) {                                                \
+                                if (__ac_iseither(h->flags, j) == 0) {                                        \
+                                        khkey_t key = h->keys[j];                                                        \
+                                        khval_t val;                                                                                \
+                                        khint_t new_mask;                                                                        \
+                                        new_mask = new_n_buckets - 1;                                                 \
+                                        if (kh_is_map) val = h->vals[j];                                        \
+                                        __ac_set_isdel_true(h->flags, j);                                        \
+                                        while (1) { /* kick-out process; sort of like in Cuckoo hashing */ \
+                                                khint_t k, i, step = 0; \
+                                                k = __hash_func(key);                                                        \
+                                                i = k & new_mask;                                                                \
+                                                while (!__ac_isempty(new_flags, i)) i = (i + (++step)) & new_mask; \
+                                                __ac_set_isempty_false(new_flags, i);                        \
+                                                if (i < h->n_buckets && __ac_iseither(h->flags, i) == 0) { /* kick out the existing element */ \
+                                                        { khkey_t tmp = h->keys[i]; h->keys[i] = key; key = tmp; } \
+                                                        if (kh_is_map) { khval_t tmp = h->vals[i]; h->vals[i] = val; val = tmp; } \
+                                                        __ac_set_isdel_true(h->flags, i); /* mark it as deleted in the old hash table */ \
+                                                } else { /* write the element and jump out of the loop */ \
+                                                        h->keys[i] = key;                                                        \
+                                                        if (kh_is_map) h->vals[i] = val;                        \
+                                                        break;                                                                                \
+                                                }                                                                                                \
+                                        }                                                                                                        \
+                                }                                                                                                                \
+                        }                                                                                                                        \
+                        if (h->n_buckets > new_n_buckets) { /* shrink the hash table */ \
+                                h->keys = (khkey_t*)krealloc((void *)h->keys, new_n_buckets * sizeof(khkey_t)); \
+                                if (kh_is_map) h->vals = (khval_t*)krealloc((void *)h->vals, new_n_buckets * sizeof(khval_t)); \
+                        }                                                                                                                        \
+                        kfree(h->flags); /* free the working space */                                \
+                        h->flags = new_flags;                                                                                \
+                        h->n_buckets = new_n_buckets;                                                                \
+                        h->n_occupied = h->size;                                                                        \
+                        h->upper_bound = (khint_t)(h->n_buckets * __ac_HASH_UPPER + 0.5); \
+                }                                                                                                                                \
+                return 0;                                                                                                                \
+        }                                                                                                                                        \
+        SCOPE khint_t kh_put_##name(kh_##name##_t *h, khkey_t key, int *ret) \
+        {                                                                                                                                        \
+                khint_t x;                                                                                                                \
+                if (h->n_occupied >= h->upper_bound) { /* update the hash table */ \
+                        if (h->n_buckets > (h->size<<1)) {                                                        \
+                                if (kh_resize_##name(h, h->n_buckets - 1) < 0) { /* clear "deleted" elements */ \
+                                        *ret = -1; return h->n_buckets;                                                \
+                                }                                                                                                                \
+                        } else if (kh_resize_##name(h, h->n_buckets + 1) < 0) { /* expand the hash table */ \
+                                *ret = -1; return h->n_buckets;                                                        \
+                        }                                                                                                                        \
+                } /* TODO: to implement automatically shrinking; resize() already support shrinking */ \
+                {                                                                                                                                \
+                        khint_t k, i, site, last, mask = h->n_buckets - 1, step = 0; \
+                        x = site = h->n_buckets; k = __hash_func(key); i = k & mask; \
+                        if (__ac_isempty(h->flags, i)) x = i; /* for speed up */        \
+                        else {                                                                                                                \
+                                last = i; \
+                                while (!__ac_isempty(h->flags, i) && (__ac_isdel(h->flags, i) || !__hash_equal(h->keys[i], key))) { \
+                                        if (__ac_isdel(h->flags, i)) site = i;                                \
+                                        i = (i + (++step)) & mask; \
+                                        if (i == last) { x = site; break; }                                        \
+                                }                                                                                                                \
+                                if (x == h->n_buckets) {                                                                \
+                                        if (__ac_isempty(h->flags, i) && site != h->n_buckets) x = site; \
+                                        else x = i;                                                                                        \
+                                }                                                                                                                \
+                        }                                                                                                                        \
+                }                                                                                                                                \
+                if (__ac_isempty(h->flags, x)) { /* not present at all */                \
+                        h->keys[x] = key;                                                                                        \
+                        __ac_set_isboth_false(h->flags, x);                                                        \
+                        ++h->size; ++h->n_occupied;                                                                        \
+                        *ret = 1;                                                                                                        \
+                } else if (__ac_isdel(h->flags, x)) { /* deleted */                                \
+                        h->keys[x] = key;                                                                                        \
+                        __ac_set_isboth_false(h->flags, x);                                                        \
+                        ++h->size;                                                                                                        \
+                        *ret = 2;                                                                                                        \
+                } else *ret = 0; /* Don't touch h->keys[x] if present and not deleted */ \
+                return x;                                                                                                                \
+        }                                                                                                                                        \
+        SCOPE void kh_del_##name(kh_##name##_t *h, khint_t x)                                \
+        {                                                                                                                                        \
+                if (x != h->n_buckets && !__ac_iseither(h->flags, x)) {                        \
+                        __ac_set_isdel_true(h->flags, x);                                                        \
+                        --h->size;                                                                                                        \
+                }                                                                                                                                \
+        }
+
+#define KHASH_DECLARE(name, khkey_t, khval_t)                                                         \
+        __KHASH_TYPE(name, khkey_t, khval_t)                                                                 \
+        __KHASH_PROTOTYPES(name, khkey_t, khval_t)
+
+#define KHASH_INIT2(name, SCOPE, khkey_t, khval_t, kh_is_map, __hash_func, __hash_equal) \
+        __KHASH_TYPE(name, khkey_t, khval_t)                                                                 \
+        __KHASH_IMPL(name, SCOPE, khkey_t, khval_t, kh_is_map, __hash_func, __hash_equal)
+
+#define KHASH_INIT(name, khkey_t, khval_t, kh_is_map, __hash_func, __hash_equal) \
+        KHASH_INIT2(name, static kh_inline, khkey_t, khval_t, kh_is_map, __hash_func, __hash_equal)
+
+/* --- BEGIN OF HASH FUNCTIONS --- */
+
+/*! @function
+  @abstract     Integer hash function
+  @param  key   The integer [khint32_t]
+  @return       The hash value [khint_t]
+ */
+#define kh_int_hash_func(key) (khint32_t)(key)
+/*! @function
+  @abstract     Integer comparison function
+ */
+#define kh_int_hash_equal(a, b) ((a) == (b))
+/*! @function
+  @abstract     64-bit integer hash function
+  @param  key   The integer [khint64_t]
+  @return       The hash value [khint_t]
+ */
+#define kh_int64_hash_func(key) (khint32_t)((key)>>33^(key)^(key)<<11)
+/*! @function
+  @abstract     64-bit integer comparison function
+ */
+#define kh_int64_hash_equal(a, b) ((a) == (b))
+/*! @function
+  @abstract     const char* hash function
+  @param  s     Pointer to a null terminated string
+  @return       The hash value
+ */
+static kh_inline khint_t __ac_X31_hash_string(const char *s)
+{
+        khint_t h = (khint_t)*s;
+        if (h) for (++s ; *s; ++s) h = (h << 5) - h + (khint_t)*s;
+        return h;
+}
+/*! @function
+  @abstract     Another interface to const char* hash function
+  @param  key   Pointer to a null terminated string [const char*]
+  @return       The hash value [khint_t]
+ */
+#define kh_str_hash_func(key) __ac_X31_hash_string(key)
+/*! @function
+  @abstract     Const char* comparison function
+ */
+#define kh_str_hash_equal(a, b) (strcmp(a, b) == 0)
+
+static kh_inline khint_t __ac_Wang_hash(khint_t key)
+{
+    key += ~(key << 15);
+    key ^=  (key >> 10);
+    key +=  (key << 3);
+    key ^=  (key >> 6);
+    key += ~(key << 11);
+    key ^=  (key >> 16);
+    return key;
+}
+#define kh_int_hash_func2(k) __ac_Wang_hash((khint_t)key)
+
+/* --- END OF HASH FUNCTIONS --- */
+
+/* Other convenient macros... */
+
+/*!
+  @abstract Type of the hash table.
+  @param  name  Name of the hash table [symbol]
+ */
+#define khash_t(name) kh_##name##_t
+
+/*! @function
+  @abstract     Initiate a hash table.
+  @param  name  Name of the hash table [symbol]
+  @return       Pointer to the hash table [khash_t(name)*]
+ */
+#define kh_init(name) kh_init_##name()
+
+/*! @function
+  @abstract     Destroy a hash table.
+  @param  name  Name of the hash table [symbol]
+  @param  h     Pointer to the hash table [khash_t(name)*]
+ */
+#define kh_destroy(name, h) kh_destroy_##name(h)
+
+/*! @function
+  @abstract     Reset a hash table without deallocating memory.
+  @param  name  Name of the hash table [symbol]
+  @param  h     Pointer to the hash table [khash_t(name)*]
+ */
+#define kh_clear(name, h) kh_clear_##name(h)
+
+/*! @function
+  @abstract     Resize a hash table.
+  @param  name  Name of the hash table [symbol]
+  @param  h     Pointer to the hash table [khash_t(name)*]
+  @param  s     New size [khint_t]
+ */
+#define kh_resize(name, h, s) kh_resize_##name(h, s)
+
+/*! @function
+  @abstract     Insert a key to the hash table.
+  @param  name  Name of the hash table [symbol]
+  @param  h     Pointer to the hash table [khash_t(name)*]
+  @param  k     Key [type of keys]
+  @param  r     Extra return code: -1 if the operation failed;
+                0 if the key is present in the hash table;
+                1 if the bucket is empty (never used); 2 if the element in
+                                the bucket has been deleted [int*]
+  @return       Iterator to the inserted element [khint_t]
+ */
+#define kh_put(name, h, k, r) kh_put_##name(h, k, r)
+
+/*! @function
+  @abstract     Retrieve a key from the hash table.
+  @param  name  Name of the hash table [symbol]
+  @param  h     Pointer to the hash table [khash_t(name)*]
+  @param  k     Key [type of keys]
+  @return       Iterator to the found element, or kh_end(h) if the element is absent [khint_t]
+ */
+#define kh_get(name, h, k) kh_get_##name(h, k)
+
+/*! @function
+  @abstract     Remove a key from the hash table.
+  @param  name  Name of the hash table [symbol]
+  @param  h     Pointer to the hash table [khash_t(name)*]
+  @param  k     Iterator to the element to be deleted [khint_t]
+ */
+#define kh_del(name, h, k) kh_del_##name(h, k)
+
+/*! @function
+  @abstract     Test whether a bucket contains data.
+  @param  h     Pointer to the hash table [khash_t(name)*]
+  @param  x     Iterator to the bucket [khint_t]
+  @return       1 if containing data; 0 otherwise [int]
+ */
+#define kh_exist(h, x) (!__ac_iseither((h)->flags, (x)))
+
+/*! @function
+  @abstract     Get key given an iterator
+  @param  h     Pointer to the hash table [khash_t(name)*]
+  @param  x     Iterator to the bucket [khint_t]
+  @return       Key [type of keys]
+ */
+#define kh_key(h, x) ((h)->keys[x])
+
+/*! @function
+  @abstract     Get value given an iterator
+  @param  h     Pointer to the hash table [khash_t(name)*]
+  @param  x     Iterator to the bucket [khint_t]
+  @return       Value [type of values]
+  @discussion   For hash sets, calling this results in segfault.
+ */
+#define kh_val(h, x) ((h)->vals[x])
+
+/*! @function
+  @abstract     Alias of kh_val()
+ */
+#define kh_value(h, x) ((h)->vals[x])
+
+/*! @function
+  @abstract     Get the start iterator
+  @param  h     Pointer to the hash table [khash_t(name)*]
+  @return       The start iterator [khint_t]
+ */
+#define kh_begin(h) (khint_t)(0)
+
+/*! @function
+  @abstract     Get the end iterator
+  @param  h     Pointer to the hash table [khash_t(name)*]
+  @return       The end iterator [khint_t]
+ */
+#define kh_end(h) ((h)->n_buckets)
+
+/*! @function
+  @abstract     Get the number of elements in the hash table
+  @param  h     Pointer to the hash table [khash_t(name)*]
+  @return       Number of elements in the hash table [khint_t]
+ */
+#define kh_size(h) ((h)->size)
+
+/*! @function
+  @abstract     Get the number of buckets in the hash table
+  @param  h     Pointer to the hash table [khash_t(name)*]
+  @return       Number of buckets in the hash table [khint_t]
+ */
+#define kh_n_buckets(h) ((h)->n_buckets)
+
+/*! @function
+  @abstract     Iterate over the entries in the hash table
+  @param  h     Pointer to the hash table [khash_t(name)*]
+  @param  kvar  Variable to which key will be assigned
+  @param  vvar  Variable to which value will be assigned
+  @param  code  Block of code to execute
+ */
+#define kh_foreach(h, kvar, vvar, code) { khint_t __i;                \
+        for (__i = kh_begin(h); __i != kh_end(h); ++__i) {                \
+                if (!kh_exist(h,__i)) continue;                                                \
+                (kvar) = kh_key(h,__i);                                                                \
+                (vvar) = kh_val(h,__i);                                                                \
+                code;                                                                                                \
+        } }
+
+/*! @function
+  @abstract     Iterate over the values in the hash table
+  @param  h     Pointer to the hash table [khash_t(name)*]
+  @param  vvar  Variable to which value will be assigned
+  @param  code  Block of code to execute
+ */
+#define kh_foreach_value(h, vvar, code) { khint_t __i;                \
+        for (__i = kh_begin(h); __i != kh_end(h); ++__i) {                \
+                if (!kh_exist(h,__i)) continue;                                                \
+                (vvar) = kh_val(h,__i);                                                                \
+                code;                                                                                                \
+        } }
+
+/* More conenient interfaces */
+
+/*! @function
+  @abstract     Instantiate a hash set containing integer keys
+  @param  name  Name of the hash table [symbol]
+ */
+#define KHASH_SET_INIT_INT(name)                                                                                \
+        KHASH_INIT(name, khint32_t, char, 0, kh_int_hash_func, kh_int_hash_equal)
+
+/*! @function
+  @abstract     Instantiate a hash map containing integer keys
+  @param  name  Name of the hash table [symbol]
+  @param  khval_t  Type of values [type]
+ */
+#define KHASH_MAP_INIT_INT(name, khval_t)                                                                \
+        KHASH_INIT(name, khint32_t, khval_t, 1, kh_int_hash_func, kh_int_hash_equal)
+
+/*! @function
+  @abstract     Instantiate a hash map containing 64-bit integer keys
+  @param  name  Name of the hash table [symbol]
+ */
+#define KHASH_SET_INIT_INT64(name)                                                                                \
+        KHASH_INIT(name, khint64_t, char, 0, kh_int64_hash_func, kh_int64_hash_equal)
+
+/*! @function
+  @abstract     Instantiate a hash map containing 64-bit integer keys
+  @param  name  Name of the hash table [symbol]
+  @param  khval_t  Type of values [type]
+ */
+#define KHASH_MAP_INIT_INT64(name, khval_t)                                                                \
+        KHASH_INIT(name, khint64_t, khval_t, 1, kh_int64_hash_func, kh_int64_hash_equal)
+
+typedef const char *kh_cstr_t;
+/*! @function
+  @abstract     Instantiate a hash map containing const char* keys
+  @param  name  Name of the hash table [symbol]
+ */
+#define KHASH_SET_INIT_STR(name)                                                                                \
+        KHASH_INIT(name, kh_cstr_t, char, 0, kh_str_hash_func, kh_str_hash_equal)
+
+/*! @function
+  @abstract     Instantiate a hash map containing const char* keys
+  @param  name  Name of the hash table [symbol]
+  @param  khval_t  Type of values [type]
+ */
+#define KHASH_MAP_INIT_STR(name, khval_t)                                                                \
+        KHASH_INIT(name, kh_cstr_t, khval_t, 1, kh_str_hash_func, kh_str_hash_equal)
+
+#endif /* __AC_KHASH_H */
diff --git a/svc.c b/svc.c
index 38f362c..f347a7e 100644
--- a/svc.c
+++ b/svc.c
@@ -6,6 +6,7 @@
 #define _GNU_SOURCE 1 /* needed for _ATFILE_SOURCE on glibc 2.5 - 2.9 */
 #include <dirent.h> /* needed for FreeBSD */
 #include "cmogstored.h"
+#include "dev.h"
 
 /* same default as MogileFS upstream */
 static pthread_mutex_t svc_lock = PTHREAD_MUTEX_INITIALIZER;
@@ -34,8 +35,13 @@ static void svc_free(void *ptr)
         mog_free(svc->docroot);
         if (svc->by_st_dev)
                 hash_free(svc->by_st_dev);
-        if (svc->by_mog_devid)
-                hash_free(svc->by_mog_devid);
+        if (svc->by_mog_devid) {
+                struct mog_dev *dev;
+                khash_t(by_mog_devid) *h = svc->by_mog_devid;
+
+                mog_kh_foreach_key(h, dev, mog_dev_free(dev));
+                kh_destroy(by_mog_devid, h);
+        }
         free(svc);
 }
 
@@ -139,8 +145,7 @@ struct mog_svc * mog_svc_new(const char *docroot)
         svc->idle_timeout = 5;
         CHECK(int, 0, pthread_mutex_init(&svc->devstats_lock, NULL));
         CHECK(int, 0, pthread_mutex_init(&svc->by_mog_devid_lock, NULL));
-        svc->by_mog_devid = hash_initialize(7, NULL, mog_dev_hash,
-                                        mog_dev_cmp, mog_dev_free);
+        svc->by_mog_devid = kh_init(by_mog_devid);
         mog_oom_if_null(svc->by_mog_devid);
 
         switch (hash_insert_if_absent(by_docroot, svc, NULL)) {
diff --git a/svc_dev.c b/svc_dev.c
index ea41c11..3a87800 100644
--- a/svc_dev.c
+++ b/svc_dev.c
@@ -4,6 +4,7 @@
  */
 #include "cmogstored.h"
 #include "compat_memstream.h"
+#include "dev.h"
 
 /*
  * maps multiple "devXXX" directories to the device.
@@ -12,7 +13,7 @@
  */
 struct mog_devlist {
         dev_t st_dev;
-        Hash_table *by_mogdevid;
+        khash_t(by_mog_devid) *by_mogdevid;
 };
 
 static size_t devlist_hash(const void *x, size_t tablesize)
@@ -34,7 +35,7 @@ static void devlist_free(void *x)
 {
         struct mog_devlist *devlist = x;
 
-        hash_free(devlist->by_mogdevid);
+        kh_destroy(by_mog_devid, devlist->by_mogdevid);
         free(devlist);
 }
 
@@ -43,15 +44,7 @@ static struct mog_devlist * mog_devlist_new(dev_t st_dev)
         struct mog_devlist *devlist = xmalloc(sizeof(struct mog_devlist));
 
         devlist->st_dev = st_dev;
-        devlist->by_mogdevid = hash_initialize(7, NULL,
-                                               mog_dev_hash, mog_dev_cmp,
-
-                                               /*
-                                                * elements are freed when
-                                                * svc->by_mog_devid is freed
-                                                */
-                                               NULL);
-
+        devlist->by_mogdevid = kh_init(by_mog_devid);
         mog_oom_if_null(devlist->by_mogdevid);
 
         return devlist;
@@ -108,7 +101,8 @@ static int svc_scandev(struct mog_svc *svc, unsigned *nr, mog_scandev_cb cb)
                 size_t len = strlen(ent->d_name);
                 struct mog_dev *dev;
                 struct mog_devlist *devlist;
-                Hash_table *devhash;
+                khash_t(by_mog_devid) *devhash;
+                int ret;
 
                 if (len <= 3) continue;
                 if (memcmp("dev", ent->d_name, 3) != 0) continue;
@@ -126,14 +120,16 @@ static int svc_scandev(struct mog_svc *svc, unsigned *nr, mog_scandev_cb cb)
                 if (cb)
                         rc |= cb(dev, svc); /* mog_dev_mkusage */
 
-                switch (hash_insert_if_absent(devhash, dev, NULL)) {
+                kh_put(by_mog_devid, devhash, dev, &ret);
+                switch (ret) {
                 case 0:
                         /* do not free dev, it is in svc->by_mog_devid */
                         syslog(LOG_ERR,
                                "%s/%s seen twice in readdir (BUG?)",
                                svc->docroot, ent->d_name);
                         break;
-                case 1:
+                case 1: /* never-used bucket */
+                case 2: /* deleted bucket */
                         (*nr)++;
                         break;
                 default: mog_oom(); /* -1 */
@@ -164,9 +160,11 @@ static bool write_dev_stats(void *entry, void *filep)
 static bool write_devlist_stats(void *entry, void *filep)
 {
         struct mog_devlist *devlist = entry;
-        FILE **fp ;
+        FILE **fp;
+        struct mog_dev *dev;
+        khash_t(by_mog_devid) *h = devlist->by_mogdevid;
 
-        hash_do_for_each(devlist->by_mogdevid, write_dev_stats, filep);
+        mog_kh_foreach_key(h, dev, write_dev_stats(dev, filep));
         fp = filep;
 
         /* *filep becomes NULL on errors */
@@ -314,17 +312,25 @@ static void svc_rescale_warn_fix_capa(struct mog_svc *svc, unsigned ndev_new)
 
 static void mog_svc_dev_rescale_all(struct mog_svc *svc)
 {
+        struct mog_dev *dev;
+        khash_t(by_mog_devid) *h;
+
         /* iterate through each device of this svc */
         CHECK(int, 0, pthread_mutex_lock(&svc->by_mog_devid_lock));
-        hash_do_for_each(svc->by_mog_devid, mog_dev_user_rescale_i, svc);
+        h = svc->by_mog_devid;
+        mog_kh_foreach_key(h, dev, mog_dev_user_rescale_i(dev, svc));
         CHECK(int, 0, pthread_mutex_unlock(&svc->by_mog_devid_lock));
 }
 
 void mog_svc_dev_requeue_prepare(struct mog_svc *svc)
 {
+        struct mog_dev *dev;
+        khash_t(by_mog_devid) *h;
+
         /* iterate through each device of this svc */
         CHECK(int, 0, pthread_mutex_lock(&svc->by_mog_devid_lock));
-        hash_do_for_each(svc->by_mog_devid, mog_dev_requeue_prepare, svc);
+        h = svc->by_mog_devid;
+        mog_kh_foreach_key(h, dev, mog_dev_requeue_prepare(dev, svc));
         CHECK(int, 0, pthread_mutex_unlock(&svc->by_mog_devid_lock));
 }