From: Minchan Kim <minchan@kernel.org>
To: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Subject: Re: [RFC][PATCHv2 5/8] zsmalloc: introduce zs_can_compact() function
Date: Tue, 16 Jun 2015 23:19:14 +0900 [thread overview]
Message-ID: <20150616141914.GC31387@blaptop> (raw)
In-Reply-To: <1433505838-23058-6-git-send-email-sergey.senozhatsky@gmail.com>
On Fri, Jun 05, 2015 at 09:03:55PM +0900, Sergey Senozhatsky wrote:
> This function checks if class compaction will free any pages.
> Rephrasing -- do we have enough unused objects to form at least
> one ZS_EMPTY page and free it. It aborts compaction if class
> compaction will not result in any (further) savings.
>
> EXAMPLE (this debug output is not part of this patch set):
>
> -- class size
> -- number of allocated objects
> -- number of used objects,
> -- estimated number of pages that will be freed
>
> [..]
> class-3072 objs:24652 inuse:24628 maxobjs-per-page:4 pages-tofree:6
Please use clear term. We have been used zspage as cluster of pages.
maxobjs-per-zspage:4
And say what is pages-per-zspage for each class.
then, write how you calculate it for easy reviewing.
* class-3072
* pages-per-zspage: 3
* maxobjs-per-zspage = 4
In your example, allocated obj = 24652 and inuse obj = 24628
so 24652 - 24628 = 24 = 4(ie, maxobjs-per-zspage) * 6
so we can save 6 zspage. A zspage includes 3 pages so we can
save 3 * 6 = 18 pages via compaction.
> class-3072 objs:24648 inuse:24628 maxobjs-per-page:4 pages-tofree:5
> class-3072 objs:24644 inuse:24628 maxobjs-per-page:4 pages-tofree:4
> class-3072 objs:24640 inuse:24628 maxobjs-per-page:4 pages-tofree:3
> class-3072 objs:24636 inuse:24628 maxobjs-per-page:4 pages-tofree:2
> class-3072 objs:24632 inuse:24628 maxobjs-per-page:4 pages-tofree:1
> class-2720 objs:17970 inuse:17966 maxobjs-per-page:3 pages-tofree:1
> class-2720 objs:17967 inuse:17966 maxobjs-per-page:3 pages-tofree:0
> class-2720: Compaction is useless
> class-2448 objs:7680 inuse:7674 maxobjs-per-page:5 pages-tofree:1
> class-2336 objs:13510 inuse:13500 maxobjs-per-page:7 pages-tofree:1
> class-2336 objs:13503 inuse:13500 maxobjs-per-page:7 pages-tofree:0
> class-2336: Compaction is useless
> class-1808 objs:1161 inuse:1154 maxobjs-per-page:9 pages-tofree:0
> class-1808: Compaction is useless
> class-1744 objs:2135 inuse:2131 maxobjs-per-page:7 pages-tofree:0
> class-1744: Compaction is useless
> class-1536 objs:1328 inuse:1323 maxobjs-per-page:8 pages-tofree:0
> class-1536: Compaction is useless
> class-1488 objs:8855 inuse:8847 maxobjs-per-page:11 pages-tofree:0
> class-1488: Compaction is useless
> class-1360 objs:14880 inuse:14878 maxobjs-per-page:3 pages-tofree:0
> class-1360: Compaction is useless
> class-1248 objs:3588 inuse:3577 maxobjs-per-page:13 pages-tofree:0
> class-1248: Compaction is useless
> class-1216 objs:3380 inuse:3372 maxobjs-per-page:10 pages-tofree:0
> class-1216: Compaction is useless
> class-1168 objs:3416 inuse:3401 maxobjs-per-page:7 pages-tofree:2
> class-1168 objs:3409 inuse:3401 maxobjs-per-page:7 pages-tofree:1
> class-1104 objs:605 inuse:599 maxobjs-per-page:11 pages-tofree:0
> class-1104: Compaction is useless
> [..]
>
> Every "Compaction is useless" indicates that we saved some CPU cycles.
>
> class-1104 has
> 605 object allocated
> 599 objects used
> 11 objects per-page
>
> Even if we have a ALMOST_EMPTY zspage, we still don't have enough room to
> migrate all of its objects and free this zspage; so compaction will not
> make a lot of sense here, it's better to just leave it as is.
>
> Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
> ---
> mm/zsmalloc.c | 25 +++++++++++++++++++++++++
> 1 file changed, 25 insertions(+)
>
> diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
> index 0453347..5d8f1d4 100644
> --- a/mm/zsmalloc.c
> +++ b/mm/zsmalloc.c
> @@ -1682,6 +1682,28 @@ static struct page *isolate_source_page(struct size_class *class)
> return page;
> }
>
> +/*
> + * Make sure that we actually can compact this class,
> + * IOW if migration will empty at least one page.
free at least one zspage
> + *
> + * Should be called under class->lock
> + */
> +static unsigned long zs_can_compact(struct size_class *class)
> +{
> + /*
> + * Calculate how many unused allocated objects we
> + * have and see if we can free any zspages. Otherwise,
> + * compaction can just move objects back and forth w/o
> + * any memory gain.
> + */
> + unsigned long 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);
I don't think we need division and make it simple.
return obj_wasted >= get_maxobj_per_zspage
> + return obj_wasted;
> +}
> +
> static unsigned long __zs_compact(struct zs_pool *pool,
> struct size_class *class)
> {
> @@ -1695,6 +1717,9 @@ static unsigned long __zs_compact(struct zs_pool *pool,
>
> BUG_ON(!is_first_page(src_page));
>
> + if (!zs_can_compact(class))
> + break;
> +
> cc.index = 0;
> cc.s_page = src_page;
>
> --
> 2.4.2.387.gf86f31a
>
--
Kind regards,
Minchan Kim
WARNING: multiple messages have this Message-ID (diff)
From: Minchan Kim <minchan@kernel.org>
To: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>
Subject: Re: [RFC][PATCHv2 5/8] zsmalloc: introduce zs_can_compact() function
Date: Tue, 16 Jun 2015 23:19:14 +0900 [thread overview]
Message-ID: <20150616141914.GC31387@blaptop> (raw)
In-Reply-To: <1433505838-23058-6-git-send-email-sergey.senozhatsky@gmail.com>
On Fri, Jun 05, 2015 at 09:03:55PM +0900, Sergey Senozhatsky wrote:
> This function checks if class compaction will free any pages.
> Rephrasing -- do we have enough unused objects to form at least
> one ZS_EMPTY page and free it. It aborts compaction if class
> compaction will not result in any (further) savings.
>
> EXAMPLE (this debug output is not part of this patch set):
>
> -- class size
> -- number of allocated objects
> -- number of used objects,
> -- estimated number of pages that will be freed
>
> [..]
> class-3072 objs:24652 inuse:24628 maxobjs-per-page:4 pages-tofree:6
Please use clear term. We have been used zspage as cluster of pages.
maxobjs-per-zspage:4
And say what is pages-per-zspage for each class.
then, write how you calculate it for easy reviewing.
* class-3072
* pages-per-zspage: 3
* maxobjs-per-zspage = 4
In your example, allocated obj = 24652 and inuse obj = 24628
so 24652 - 24628 = 24 = 4(ie, maxobjs-per-zspage) * 6
so we can save 6 zspage. A zspage includes 3 pages so we can
save 3 * 6 = 18 pages via compaction.
> class-3072 objs:24648 inuse:24628 maxobjs-per-page:4 pages-tofree:5
> class-3072 objs:24644 inuse:24628 maxobjs-per-page:4 pages-tofree:4
> class-3072 objs:24640 inuse:24628 maxobjs-per-page:4 pages-tofree:3
> class-3072 objs:24636 inuse:24628 maxobjs-per-page:4 pages-tofree:2
> class-3072 objs:24632 inuse:24628 maxobjs-per-page:4 pages-tofree:1
> class-2720 objs:17970 inuse:17966 maxobjs-per-page:3 pages-tofree:1
> class-2720 objs:17967 inuse:17966 maxobjs-per-page:3 pages-tofree:0
> class-2720: Compaction is useless
> class-2448 objs:7680 inuse:7674 maxobjs-per-page:5 pages-tofree:1
> class-2336 objs:13510 inuse:13500 maxobjs-per-page:7 pages-tofree:1
> class-2336 objs:13503 inuse:13500 maxobjs-per-page:7 pages-tofree:0
> class-2336: Compaction is useless
> class-1808 objs:1161 inuse:1154 maxobjs-per-page:9 pages-tofree:0
> class-1808: Compaction is useless
> class-1744 objs:2135 inuse:2131 maxobjs-per-page:7 pages-tofree:0
> class-1744: Compaction is useless
> class-1536 objs:1328 inuse:1323 maxobjs-per-page:8 pages-tofree:0
> class-1536: Compaction is useless
> class-1488 objs:8855 inuse:8847 maxobjs-per-page:11 pages-tofree:0
> class-1488: Compaction is useless
> class-1360 objs:14880 inuse:14878 maxobjs-per-page:3 pages-tofree:0
> class-1360: Compaction is useless
> class-1248 objs:3588 inuse:3577 maxobjs-per-page:13 pages-tofree:0
> class-1248: Compaction is useless
> class-1216 objs:3380 inuse:3372 maxobjs-per-page:10 pages-tofree:0
> class-1216: Compaction is useless
> class-1168 objs:3416 inuse:3401 maxobjs-per-page:7 pages-tofree:2
> class-1168 objs:3409 inuse:3401 maxobjs-per-page:7 pages-tofree:1
> class-1104 objs:605 inuse:599 maxobjs-per-page:11 pages-tofree:0
> class-1104: Compaction is useless
> [..]
>
> Every "Compaction is useless" indicates that we saved some CPU cycles.
>
> class-1104 has
> 605 object allocated
> 599 objects used
> 11 objects per-page
>
> Even if we have a ALMOST_EMPTY zspage, we still don't have enough room to
> migrate all of its objects and free this zspage; so compaction will not
> make a lot of sense here, it's better to just leave it as is.
>
> Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
> ---
> mm/zsmalloc.c | 25 +++++++++++++++++++++++++
> 1 file changed, 25 insertions(+)
>
> diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
> index 0453347..5d8f1d4 100644
> --- a/mm/zsmalloc.c
> +++ b/mm/zsmalloc.c
> @@ -1682,6 +1682,28 @@ static struct page *isolate_source_page(struct size_class *class)
> return page;
> }
>
> +/*
> + * Make sure that we actually can compact this class,
> + * IOW if migration will empty at least one page.
free at least one zspage
> + *
> + * Should be called under class->lock
> + */
> +static unsigned long zs_can_compact(struct size_class *class)
> +{
> + /*
> + * Calculate how many unused allocated objects we
> + * have and see if we can free any zspages. Otherwise,
> + * compaction can just move objects back and forth w/o
> + * any memory gain.
> + */
> + unsigned long 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);
I don't think we need division and make it simple.
return obj_wasted >= get_maxobj_per_zspage
> + return obj_wasted;
> +}
> +
> static unsigned long __zs_compact(struct zs_pool *pool,
> struct size_class *class)
> {
> @@ -1695,6 +1717,9 @@ static unsigned long __zs_compact(struct zs_pool *pool,
>
> BUG_ON(!is_first_page(src_page));
>
> + if (!zs_can_compact(class))
> + break;
> +
> cc.index = 0;
> cc.s_page = src_page;
>
> --
> 2.4.2.387.gf86f31a
>
--
Kind regards,
Minchan Kim
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next prev parent reply other threads:[~2015-06-16 14:19 UTC|newest]
Thread overview: 52+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-06-05 12:03 [RFC][PATCHv2 0/8] introduce automatic pool compaction Sergey Senozhatsky
2015-06-05 12:03 ` Sergey Senozhatsky
2015-06-05 12:03 ` [RFC][PATCHv2 1/8] zsmalloc: drop unused variable `nr_to_migrate' Sergey Senozhatsky
2015-06-05 12:03 ` Sergey Senozhatsky
2015-06-05 12:03 ` [RFC][PATCHv2 2/8] zsmalloc: partial page ordering within a fullness_list Sergey Senozhatsky
2015-06-05 12:03 ` Sergey Senozhatsky
2015-06-16 13:19 ` Minchan Kim
2015-06-16 13:19 ` Minchan Kim
2015-06-16 14:30 ` Sergey Senozhatsky
2015-06-16 14:30 ` Sergey Senozhatsky
2015-06-05 12:03 ` [RFC][PATCHv2 3/8] zsmalloc: lower ZS_ALMOST_FULL waterline Sergey Senozhatsky
2015-06-05 12:03 ` Sergey Senozhatsky
2015-06-16 13:37 ` Minchan Kim
2015-06-16 13:37 ` Minchan Kim
2015-06-16 14:35 ` Sergey Senozhatsky
2015-06-16 14:35 ` Sergey Senozhatsky
2015-06-05 12:03 ` [RFC][PATCHv2 4/8] zsmalloc: always keep per-class stats Sergey Senozhatsky
2015-06-05 12:03 ` Sergey Senozhatsky
2015-06-05 12:03 ` [RFC][PATCHv2 5/8] zsmalloc: introduce zs_can_compact() function Sergey Senozhatsky
2015-06-05 12:03 ` Sergey Senozhatsky
2015-06-16 14:19 ` Minchan Kim [this message]
2015-06-16 14:19 ` Minchan Kim
2015-06-16 14:41 ` Sergey Senozhatsky
2015-06-16 14:41 ` Sergey Senozhatsky
2015-06-05 12:03 ` [RFC][PATCHv2 6/8] zsmalloc: cosmetic compaction code adjustments Sergey Senozhatsky
2015-06-05 12:03 ` Sergey Senozhatsky
2015-06-05 12:03 ` [RFC][PATCHv2 7/8] zsmalloc/zram: move `num_migrated' to zs_pool Sergey Senozhatsky
2015-06-05 12:03 ` Sergey Senozhatsky
2015-06-05 12:03 ` [RFC][PATCHv2 8/8] zsmalloc: register a shrinker to trigger auto-compaction Sergey Senozhatsky
2015-06-05 12:03 ` Sergey Senozhatsky
2015-06-16 14:47 ` Minchan Kim
2015-06-16 14:47 ` Minchan Kim
2015-06-16 15:45 ` Sergey Senozhatsky
2015-06-16 15:45 ` Sergey Senozhatsky
2015-06-18 1:50 ` Minchan Kim
2015-06-18 1:50 ` Minchan Kim
2015-06-18 2:41 ` Sergey Senozhatsky
2015-06-18 2:41 ` Sergey Senozhatsky
2015-06-18 3:01 ` Sergey Senozhatsky
2015-06-18 3:01 ` Sergey Senozhatsky
2015-06-18 3:46 ` Minchan Kim
2015-06-18 3:46 ` Minchan Kim
2015-06-18 3:39 ` Minchan Kim
2015-06-18 3:39 ` Minchan Kim
2015-06-18 3:58 ` Sergey Senozhatsky
2015-06-18 3:58 ` Sergey Senozhatsky
2015-06-17 7:11 ` Sergey Senozhatsky
2015-06-17 7:11 ` Sergey Senozhatsky
2015-06-10 0:04 ` [RFC][PATCHv2 0/8] introduce automatic pool compaction Minchan Kim
2015-06-10 0:04 ` Minchan Kim
2015-06-10 0:07 ` Sergey Senozhatsky
2015-06-10 0:07 ` Sergey Senozhatsky
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