From: Vlastimil Babka <vbabka@suse.cz>
To: Mel Gorman <mgorman@techsingularity.net>,
Andrew Morton <akpm@linux-foundation.org>
Cc: Shantanu Goel <sgoel01@yahoo.com>,
Johannes Weiner <hannes@cmpxchg.org>,
LKML <linux-kernel@vger.kernel.org>,
Linux-MM <linux-mm@kvack.org>
Subject: Re: [PATCH 2/3] mm, vmscan: Only clear pgdat congested/dirty/writeback state when balanced
Date: Fri, 10 Mar 2017 10:06:34 +0100 [thread overview]
Message-ID: <49662531-a35a-3c2a-b04c-af04188d0b42@suse.cz> (raw)
In-Reply-To: <20170309075657.25121-3-mgorman@techsingularity.net>
On 03/09/2017 08:56 AM, Mel Gorman wrote:
> A pgdat tracks if recent reclaim encountered too many dirty, writeback
> or congested pages. The flags control whether kswapd writes pages back
> from reclaim context, tags pages for immediate reclaim when IO completes,
> whether processes block on wait_iff_congested and whether kswapd blocks
> when too many pages marked for immediate reclaim are encountered.
>
> The state is cleared in a check function with side-effects. With the patch
> "mm, vmscan: fix zone balance check in prepare_kswapd_sleep", the timing
> of when the bits get cleared changed. Due to the way the check works,
> it'll clear the bits if ZONE_DMA is balanced for a GFP_DMA allocation
> because it does not account for lowmem reserves properly.
>
> For the simoop workload, kswapd is not stalling when it should due to
> the premature clearing, writing pages from reclaim context like crazy and
> generally being unhelpful.
>
> This patch resets the pgdat bits related to page reclaim only when kswapd
> is going to sleep. The comparison with simoop is then
>
> 4.11.0-rc1 4.11.0-rc1 4.11.0-rc1
> vanilla fixcheck-v2 clear-v2
> Amean p50-Read 21670074.18 ( 0.00%) 20464344.18 ( 5.56%) 19786774.76 ( 8.69%)
> Amean p95-Read 25456267.64 ( 0.00%) 25721423.64 ( -1.04%) 24101956.27 ( 5.32%)
> Amean p99-Read 29369064.73 ( 0.00%) 30174230.76 ( -2.74%) 27691872.71 ( 5.71%)
> Amean p50-Write 1390.30 ( 0.00%) 1395.28 ( -0.36%) 1011.91 ( 27.22%)
> Amean p95-Write 412901.57 ( 0.00%) 37737.74 ( 90.86%) 34874.98 ( 91.55%)
> Amean p99-Write 6668722.09 ( 0.00%) 666489.04 ( 90.01%) 575449.60 ( 91.37%)
> Amean p50-Allocation 78714.31 ( 0.00%) 86286.22 ( -9.62%) 84246.26 ( -7.03%)
> Amean p95-Allocation 175533.51 ( 0.00%) 351812.27 (-100.42%) 400058.43 (-127.91%)
> Amean p99-Allocation 247003.02 ( 0.00%) 6291171.56 (-2447.00%) 10905600.00 (-4315.17%)
>
> Read latency is improved, write latency is mostly improved but allocation
> latency is regressed. kswapd is still reclaiming inefficiently,
> pages are being written back from writeback context and a host of other
> issues. However, given the change, it needed to be spelled out why the
> side-effect was moved.
>
> Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
--
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:[~2017-03-10 9:06 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-03-09 7:56 [PATCH 0/3] Reduce amount of time kswapd sleeps prematurely v2 Mel Gorman
2017-03-09 7:56 ` [PATCH 1/3] mm, vmscan: fix zone balance check in prepare_kswapd_sleep Mel Gorman
2017-03-10 9:06 ` Vlastimil Babka
2017-03-09 7:56 ` [PATCH 2/3] mm, vmscan: Only clear pgdat congested/dirty/writeback state when balanced Mel Gorman
2017-03-10 9:06 ` Vlastimil Babka [this message]
2017-03-09 7:56 ` [PATCH 3/3] mm, vmscan: Prevent kswapd sleeping prematurely due to mismatched classzone_idx Mel Gorman
-- strict thread matches above, loose matches on Subject: below --
2017-02-15 9:22 [PATCH 0/3] Reduce amount of time kswapd sleeps prematurely Mel Gorman
2017-02-15 9:22 ` [PATCH 2/3] mm, vmscan: Only clear pgdat congested/dirty/writeback state when balanced Mel Gorman
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=49662531-a35a-3c2a-b04c-af04188d0b42@suse.cz \
--to=vbabka@suse.cz \
--cc=akpm@linux-foundation.org \
--cc=hannes@cmpxchg.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=mgorman@techsingularity.net \
--cc=sgoel01@yahoo.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox