From: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> To: Dan Streetman <ddstreet@ieee.org> Cc: Vlastimil Babka <vbabka@suse.cz>, Vitaly Wool <vitalywool@gmail.com>, Minchan Kim <minchan@kernel.org>, Sergey Senozhatsky <sergey.senozhatsky@gmail.com>, LKML <linux-kernel@vger.kernel.org>, Linux-MM <linux-mm@kvack.org> Subject: Re: [PATCH 0/3] allow zram to use zbud as underlying allocator Date: Tue, 15 Sep 2015 13:22:16 +0900 [thread overview] Message-ID: <20150915042216.GE1860@swordfish> (raw) In-Reply-To: <CALZtONCKCTRP5r0u5iXYHsQ=uxA-B+1M=4=RPGtFiwo4EOpzeg@mail.gmail.com> On (09/15/15 00:08), Dan Streetman wrote: [..] > > it doesn't. but it has a complex (compared to zbud) way of storing > pages - many different classes, which each are made up of zspages, > which contain multiple actual pages to store some number of > specifically sized objects. So it can get fragmented, with lots of > zspages with empty spaces for objects. That's what the recently added > zsmalloc compaction addresses, by scanning all the zspages in all the > classes and compacting zspages within each class. > correct. a bit of internals: we don't scan all the zspages every time. each class has stats for allocated used objects, allocated used objects, etc. so we 'compact' only classes that can be compacted: static unsigned long zs_can_compact(struct size_class *class) { unsigned long obj_wasted; obj_wasted = zs_stat_get(class, OBJ_ALLOCATED) - zs_stat_get(class, OBJ_USED); obj_wasted /= get_maxobj_per_zspage(class->size, class->pages_per_zspage); return obj_wasted * class->pages_per_zspage; } if we can free any zspages (which is at least one page), then we attempt to do so. is compaction the root cause of the symptoms Vitaly observe? Vitaly, if you disable compaction: --- diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c index 14fc466..d9b5427 100644 --- a/mm/zsmalloc.c +++ b/mm/zsmalloc.c @@ -1944,8 +1944,9 @@ struct zs_pool *zs_create_pool(char *name, gfp_t flags) * Not critical, we still can use the pool * and user can trigger compaction manually. */ - if (zs_register_shrinker(pool) == 0) +/* if (zs_register_shrinker(pool) == 0) pool->shrinker_enabled = true; +*/ return pool; err: --- does the 'problem' go away? > but I haven't followed most of the recent zsmalloc updates too > closely, so I may be totally wrong :-) > > zbud is much simpler; since it just uses buddied pairs, it simply > keeps a list of zbud page with only 1 compressed page stored in it. > There is still the possibility of fragmentation, but since it's > simple, it's much smaller. And there is no compaction implemented in > it, currently. The downside, as we all know, is worse efficiency in > storing compressed pages - it can't do better than 2:1. > -ss
WARNING: multiple messages have this Message-ID (diff)
From: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com> To: Dan Streetman <ddstreet@ieee.org> Cc: Vlastimil Babka <vbabka@suse.cz>, Vitaly Wool <vitalywool@gmail.com>, Minchan Kim <minchan@kernel.org>, Sergey Senozhatsky <sergey.senozhatsky@gmail.com>, LKML <linux-kernel@vger.kernel.org>, Linux-MM <linux-mm@kvack.org> Subject: Re: [PATCH 0/3] allow zram to use zbud as underlying allocator Date: Tue, 15 Sep 2015 13:22:16 +0900 [thread overview] Message-ID: <20150915042216.GE1860@swordfish> (raw) In-Reply-To: <CALZtONCKCTRP5r0u5iXYHsQ=uxA-B+1M=4=RPGtFiwo4EOpzeg@mail.gmail.com> On (09/15/15 00:08), Dan Streetman wrote: [..] > > it doesn't. but it has a complex (compared to zbud) way of storing > pages - many different classes, which each are made up of zspages, > which contain multiple actual pages to store some number of > specifically sized objects. So it can get fragmented, with lots of > zspages with empty spaces for objects. That's what the recently added > zsmalloc compaction addresses, by scanning all the zspages in all the > classes and compacting zspages within each class. > correct. a bit of internals: we don't scan all the zspages every time. each class has stats for allocated used objects, allocated used objects, etc. so we 'compact' only classes that can be compacted: static unsigned long zs_can_compact(struct size_class *class) { unsigned long obj_wasted; obj_wasted = zs_stat_get(class, OBJ_ALLOCATED) - zs_stat_get(class, OBJ_USED); obj_wasted /= get_maxobj_per_zspage(class->size, class->pages_per_zspage); return obj_wasted * class->pages_per_zspage; } if we can free any zspages (which is at least one page), then we attempt to do so. is compaction the root cause of the symptoms Vitaly observe? Vitaly, if you disable compaction: --- diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c index 14fc466..d9b5427 100644 --- a/mm/zsmalloc.c +++ b/mm/zsmalloc.c @@ -1944,8 +1944,9 @@ struct zs_pool *zs_create_pool(char *name, gfp_t flags) * Not critical, we still can use the pool * and user can trigger compaction manually. */ - if (zs_register_shrinker(pool) == 0) +/* if (zs_register_shrinker(pool) == 0) pool->shrinker_enabled = true; +*/ return pool; err: --- does the 'problem' go away? > but I haven't followed most of the recent zsmalloc updates too > closely, so I may be totally wrong :-) > > zbud is much simpler; since it just uses buddied pairs, it simply > keeps a list of zbud page with only 1 compressed page stored in it. > There is still the possibility of fragmentation, but since it's > simple, it's much smaller. And there is no compaction implemented in > it, currently. The downside, as we all know, is worse efficiency in > storing compressed pages - it can't do better than 2:1. > -ss -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>
next prev parent reply other threads:[~2015-09-15 4:21 UTC|newest] Thread overview: 63+ messages / expand[flat|nested] mbox.gz Atom feed top 2015-09-14 13:49 [PATCH 0/3] allow zram to use zbud as underlying allocator Vitaly Wool 2015-09-14 13:49 ` Vitaly Wool 2015-09-14 13:50 ` [PATCH 1/3] zram: make max_zpage_size configurable Vitaly Wool 2015-09-14 13:50 ` Vitaly Wool 2015-09-15 1:00 ` Sergey Senozhatsky 2015-09-15 1:00 ` Sergey Senozhatsky 2015-09-15 7:18 ` Vitaly Wool 2015-09-15 7:38 ` Sergey Senozhatsky 2015-09-15 7:38 ` Sergey Senozhatsky 2015-09-15 5:42 ` Dan Streetman 2015-09-15 5:42 ` Dan Streetman 2015-09-15 6:08 ` Sergey Senozhatsky 2015-09-15 6:08 ` Sergey Senozhatsky 2015-09-14 13:51 ` [PATCH 2/3] zpool/zsmalloc/zbud: align on interfaces Vitaly Wool 2015-09-14 13:51 ` Vitaly Wool 2015-09-15 1:06 ` Sergey Senozhatsky 2015-09-15 1:06 ` Sergey Senozhatsky 2015-09-15 5:09 ` Dan Streetman 2015-09-15 5:09 ` Dan Streetman 2015-09-14 13:55 ` [PATCH 3/3] zram: use common zpool interface Vitaly Wool 2015-09-14 13:55 ` Vitaly Wool 2015-09-15 1:12 ` Sergey Senozhatsky 2015-09-15 1:12 ` Sergey Senozhatsky 2015-09-15 6:03 ` Dan Streetman 2015-09-15 6:03 ` Dan Streetman 2015-09-14 14:01 ` [PATCH 0/3] allow zram to use zbud as underlying allocator Vlastimil Babka 2015-09-14 14:01 ` Vlastimil Babka 2015-09-14 14:12 ` Vitaly Wool 2015-09-14 14:12 ` Vitaly Wool 2015-09-14 14:14 ` Vlastimil Babka 2015-09-14 14:14 ` Vlastimil Babka 2015-09-15 4:08 ` Dan Streetman 2015-09-15 4:08 ` Dan Streetman 2015-09-15 4:22 ` Sergey Senozhatsky [this message] 2015-09-15 4:22 ` Sergey Senozhatsky 2015-09-17 6:21 ` Vlastimil Babka 2015-09-17 6:21 ` Vlastimil Babka 2015-09-17 9:19 ` Sergey Senozhatsky 2015-09-17 9:19 ` Sergey Senozhatsky 2015-09-15 0:49 ` Sergey Senozhatsky 2015-09-15 0:49 ` Sergey Senozhatsky 2015-09-15 6:13 ` Minchan Kim 2015-09-15 6:13 ` Minchan Kim 2015-09-25 9:54 ` Vitaly Wool 2015-09-25 9:54 ` Vitaly Wool 2015-09-30 7:52 ` Minchan Kim 2015-09-30 7:52 ` Minchan Kim 2015-09-30 8:01 ` Vitaly Wool 2015-09-30 8:01 ` Vitaly Wool 2015-09-30 8:13 ` Minchan Kim 2015-09-30 8:13 ` Minchan Kim 2015-09-30 8:18 ` Vitaly Wool 2015-09-30 8:18 ` Vitaly Wool 2015-09-30 15:37 ` Vlastimil Babka 2015-09-30 15:37 ` Vlastimil Babka 2015-09-30 15:46 ` Vitaly Wool 2015-09-30 15:46 ` Vitaly Wool 2015-10-01 7:52 ` Vlastimil Babka 2015-10-01 7:52 ` Vlastimil Babka 2015-10-10 9:33 ` Vitaly Wool 2015-10-10 9:33 ` Vitaly Wool 2015-10-14 13:28 ` Vlastimil Babka 2015-10-14 13:28 ` Vlastimil Babka
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