From: Al Viro <viro@zeniv.linux.org.uk>
To: Dave Chinner <david@fromorbit.com>
Cc: linux-fsdevel@vger.kernel.org, linux-block@vger.kernel.org,
linux-cachefs@redhat.com, dhowells@redhat.com,
gfs2@lists.linux.dev, dm-devel@lists.linux.dev,
linux-security-module@vger.kernel.org, selinux@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH 01/11] lib/dlock-list: Distributed and lock-protected lists
Date: Thu, 7 Dec 2023 02:23:57 +0000 [thread overview]
Message-ID: <20231207022357.GS1674809@ZenIV> (raw)
In-Reply-To: <20231206060629.2827226-2-david@fromorbit.com>
On Wed, Dec 06, 2023 at 05:05:30PM +1100, Dave Chinner wrote:
> +static inline struct dlock_list_node *
> +__dlock_list_next_entry(struct dlock_list_node *curr,
> + struct dlock_list_iter *iter)
> +{
> + /*
> + * Find next entry
> + */
> + if (curr)
> + curr = list_next_entry(curr, list);
> +
> + if (!curr || (&curr->list == &iter->entry->list)) {
Hmm... hlist, perhaps? I mean, that way the thing becomes
if (curr)
curr = hlist_entry_safe(curr->node.next,
struct dlock_list_node, node);
if (!curr)
curr = __dlock_list_next_list(iter);
return curr;
BTW, does anybody have objections against
#define hlist_first_entry(head, type, member)
hlist_entry_safe((head)->first, type, member)
#define hlist_next_entry(pos, member)
hlist_entry_safe((pos)->member.next, typeof(*pos), member)
added in list.h?
> +static int __init cpu2idx_init(void)
> +{
> + int idx, cpu;
> +
> + idx = 0;
> + for_each_possible_cpu(cpu)
> + per_cpu(cpu2idx, cpu) = idx++;
> + return 0;
> +}
> +postcore_initcall(cpu2idx_init);
Is it early enough? Feels like that ought to be done from smp_init() or
right after it...
> +/**
> + * dlock_lists_empty - Check if all the dlock lists are empty
> + * @dlist: Pointer to the dlock_list_heads structure
> + * Return: true if list is empty, false otherwise.
> + *
> + * This can be a pretty expensive function call. If this function is required
> + * in a performance critical path, we may have to maintain a global count
> + * of the list entries in the global dlock_list_heads structure instead.
> + */
> +bool dlock_lists_empty(struct dlock_list_heads *dlist)
> +{
> + int idx;
> +
> + for (idx = 0; idx < nr_cpu_ids; idx++)
> + if (!list_empty(&dlist->heads[idx].list))
> + return false;
> + return true;
> +}
Umm... How would one use it, anyway? You'd need to stop all insertions
first, wouldn't you?
> + */
> +struct dlock_list_node *__dlock_list_next_list(struct dlock_list_iter *iter)
> +{
> + struct dlock_list_node *next;
> + struct dlock_list_head *head;
> +
> +restart:
> + if (iter->entry) {
> + spin_unlock(&iter->entry->lock);
> + iter->entry = NULL;
> + }
> +
> +next_list:
> + /*
> + * Try next list
> + */
> + if (++iter->index >= nr_cpu_ids)
> + return NULL; /* All the entries iterated */
> +
> + if (list_empty(&iter->head[iter->index].list))
> + goto next_list;
> +
> + head = iter->entry = &iter->head[iter->index];
> + spin_lock(&head->lock);
> + /*
> + * There is a slight chance that the list may become empty just
> + * before the lock is acquired. So an additional check is
> + * needed to make sure that a valid node will be returned.
> + */
> + if (list_empty(&head->list))
> + goto restart;
> +
> + next = list_entry(head->list.next, struct dlock_list_node,
> + list);
> + WARN_ON_ONCE(next->head != head);
> +
> + return next;
> +}
Perhaps something like
if (iter->entry) {
spin_unlock(&iter->entry->lock);
iter->entry = NULL;
}
while (++iter->index < nr_cpu_ids) {
struct dlock_list_head *head = &iter->head[iter->index];
if (list_empty(head->list))
continue;
spin_lock(&head->lock);
// recheck under lock
if (unlikely(list_empty(&head->list))) {
spin_unlock(&head->lock);
continue;
}
iter->entry = head;
next = list_first_entry(&head->list,
struct dlock_list_node, list);
WARN_ON_ONCE(next->head != head);
return next;
}
return NULL;
next prev parent reply other threads:[~2023-12-07 2:24 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-12-06 6:05 [PATCH 0/11] vfs: inode cache scalability improvements Dave Chinner
2023-12-06 6:05 ` [PATCH 01/11] lib/dlock-list: Distributed and lock-protected lists Dave Chinner
2023-12-07 2:23 ` Al Viro [this message]
2023-12-06 6:05 ` [PATCH 02/11] vfs: Remove unnecessary list_for_each_entry_safe() variants Dave Chinner
2023-12-07 2:26 ` Al Viro
2023-12-07 4:18 ` Kent Overstreet
2023-12-06 6:05 ` [PATCH 03/11] vfs: Use dlock list for superblock's inode list Dave Chinner
2023-12-07 2:40 ` Al Viro
2023-12-07 4:59 ` Dave Chinner
2023-12-07 5:03 ` Kent Overstreet
2023-12-06 6:05 ` [PATCH 04/11] lib/dlock-list: Make sibling CPUs share the same linked list Dave Chinner
2023-12-07 4:31 ` Kent Overstreet
2023-12-07 5:42 ` Kent Overstreet
2023-12-07 6:25 ` Dave Chinner
2023-12-07 6:49 ` Al Viro
2023-12-06 6:05 ` [PATCH 05/11] selinux: use dlist for isec inode list Dave Chinner
2023-12-06 21:52 ` Paul Moore
2023-12-06 23:04 ` Dave Chinner
2023-12-07 0:36 ` Paul Moore
2023-12-06 6:05 ` [PATCH 06/11] vfs: factor out inode hash head calculation Dave Chinner
2023-12-07 3:02 ` Al Viro
2023-12-06 6:05 ` [PATCH 07/11] hlist-bl: add hlist_bl_fake() Dave Chinner
2023-12-07 3:05 ` Al Viro
2023-12-06 6:05 ` [PATCH 08/11] vfs: inode cache conversion to hash-bl Dave Chinner
2023-12-07 4:58 ` Kent Overstreet
2023-12-07 6:03 ` Dave Chinner
2023-12-07 6:42 ` Al Viro
2023-12-06 6:05 ` [PATCH 09/11] hash-bl: explicitly initialise hash-bl heads Dave Chinner
2023-12-07 3:15 ` Al Viro
2023-12-06 6:05 ` [PATCH 10/11] list_bl: don't use bit locks for PREEMPT_RT or lockdep Dave Chinner
2023-12-07 4:16 ` Kent Overstreet
2023-12-07 4:41 ` Dave Chinner
2023-12-06 6:05 ` [PATCH 11/11] hlist-bl: introduced nested locking for dm-snap Dave Chinner
2023-12-07 17:08 ` [PATCH 0/11] vfs: inode cache scalability improvements Kent Overstreet
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