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 3/8] zsmalloc: lower ZS_ALMOST_FULL waterline
Date: Tue, 16 Jun 2015 22:37:08 +0900 [thread overview]
Message-ID: <20150616133708.GB31387@blaptop> (raw)
In-Reply-To: <1433505838-23058-4-git-send-email-sergey.senozhatsky@gmail.com>
On Fri, Jun 05, 2015 at 09:03:53PM +0900, Sergey Senozhatsky wrote:
> get_fullness_group() considers 3/4 full pages as almost empty.
> That, unfortunately, marks as ALMOST_EMPTY pages that we would
> probably like to keep in ALMOST_FULL lists.
>
> ALMOST_EMPTY:
> [..]
> inuse: 3 max_objects: 4
> inuse: 5 max_objects: 7
> inuse: 5 max_objects: 7
> inuse: 2 max_objects: 3
> [..]
>
> For "inuse: 5 max_objexts: 7" ALMOST_EMPTY page, for example,
> it'll take 2 obj_malloc to make the page FULL and 5 obj_free to
> make it EMPTY. Compaction selects ALMOST_EMPTY pages as source
> pages, which can result in extra object moves.
>
> In other words, from compaction point of view, it makes more
> sense to fill this page, rather than drain it.
>
> Decrease ALMOST_FULL waterline to 2/3 of max capacity; which is,
> of course, still imperfect, but can shorten compaction
> execution time.
However, at worst case, once compaction is done, it could remain
33% fragment space while it can remain 25% fragment space in current.
Maybe 25% wouldn't enough so we might need to scan ZS_ALMOST_FULL as
source in future. Anyway, compaction is really slow path now so
I prefer saving memory space by reduce internal fragmentation to
performance caused more copy of objects.
>
> Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
> ---
> mm/zsmalloc.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
> index cd37bda..b94e281 100644
> --- a/mm/zsmalloc.c
> +++ b/mm/zsmalloc.c
> @@ -198,7 +198,7 @@ static int zs_size_classes;
> *
> * (see: fix_fullness_group())
> */
> -static const int fullness_threshold_frac = 4;
> +static const int fullness_threshold_frac = 3;
>
> struct size_class {
> /*
> @@ -633,7 +633,7 @@ static enum fullness_group get_fullness_group(struct page *page)
> fg = ZS_EMPTY;
> else if (inuse == max_objects)
> fg = ZS_FULL;
> - else if (inuse <= 3 * max_objects / fullness_threshold_frac)
> + else if (inuse <= 2 * max_objects / fullness_threshold_frac)
> fg = ZS_ALMOST_EMPTY;
> else
> fg = ZS_ALMOST_FULL;
> --
> 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 3/8] zsmalloc: lower ZS_ALMOST_FULL waterline
Date: Tue, 16 Jun 2015 22:37:08 +0900 [thread overview]
Message-ID: <20150616133708.GB31387@blaptop> (raw)
In-Reply-To: <1433505838-23058-4-git-send-email-sergey.senozhatsky@gmail.com>
On Fri, Jun 05, 2015 at 09:03:53PM +0900, Sergey Senozhatsky wrote:
> get_fullness_group() considers 3/4 full pages as almost empty.
> That, unfortunately, marks as ALMOST_EMPTY pages that we would
> probably like to keep in ALMOST_FULL lists.
>
> ALMOST_EMPTY:
> [..]
> inuse: 3 max_objects: 4
> inuse: 5 max_objects: 7
> inuse: 5 max_objects: 7
> inuse: 2 max_objects: 3
> [..]
>
> For "inuse: 5 max_objexts: 7" ALMOST_EMPTY page, for example,
> it'll take 2 obj_malloc to make the page FULL and 5 obj_free to
> make it EMPTY. Compaction selects ALMOST_EMPTY pages as source
> pages, which can result in extra object moves.
>
> In other words, from compaction point of view, it makes more
> sense to fill this page, rather than drain it.
>
> Decrease ALMOST_FULL waterline to 2/3 of max capacity; which is,
> of course, still imperfect, but can shorten compaction
> execution time.
However, at worst case, once compaction is done, it could remain
33% fragment space while it can remain 25% fragment space in current.
Maybe 25% wouldn't enough so we might need to scan ZS_ALMOST_FULL as
source in future. Anyway, compaction is really slow path now so
I prefer saving memory space by reduce internal fragmentation to
performance caused more copy of objects.
>
> Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
> ---
> mm/zsmalloc.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/mm/zsmalloc.c b/mm/zsmalloc.c
> index cd37bda..b94e281 100644
> --- a/mm/zsmalloc.c
> +++ b/mm/zsmalloc.c
> @@ -198,7 +198,7 @@ static int zs_size_classes;
> *
> * (see: fix_fullness_group())
> */
> -static const int fullness_threshold_frac = 4;
> +static const int fullness_threshold_frac = 3;
>
> struct size_class {
> /*
> @@ -633,7 +633,7 @@ static enum fullness_group get_fullness_group(struct page *page)
> fg = ZS_EMPTY;
> else if (inuse == max_objects)
> fg = ZS_FULL;
> - else if (inuse <= 3 * max_objects / fullness_threshold_frac)
> + else if (inuse <= 2 * max_objects / fullness_threshold_frac)
> fg = ZS_ALMOST_EMPTY;
> else
> fg = ZS_ALMOST_FULL;
> --
> 2.4.2.387.gf86f31a
>
--
Kind regards,
Minchan Kim
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next prev parent reply other threads:[~2015-06-16 13:37 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 [this message]
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
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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