From: Andrew Morton <akpm@linux-foundation.org>
To: Andrey Ryabinin <aryabinin@virtuozzo.com>
Cc: Mel Gorman <mgorman@techsingularity.net>,
Tejun Heo <tj@kernel.org>, Johannes Weiner <hannes@cmpxchg.org>,
Michal Hocko <mhocko@kernel.org>,
Shakeel Butt <shakeelb@google.com>,
Steven Rostedt <rostedt@goodmis.org>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org,
cgroups@vger.kernel.org
Subject: Re: [PATCH v2 4/4] mm/vmscan: Don't mess with pgdat->flags in memcg reclaim.
Date: Thu, 5 Apr 2018 15:18:28 -0700 [thread overview]
Message-ID: <20180405151828.98b5bfb143a7a8b7dec4b153@linux-foundation.org> (raw)
In-Reply-To: <20180323152029.11084-5-aryabinin@virtuozzo.com>
On Fri, 23 Mar 2018 18:20:29 +0300 Andrey Ryabinin <aryabinin@virtuozzo.com> wrote:
> memcg reclaim may alter pgdat->flags based on the state of LRU lists
> in cgroup and its children. PGDAT_WRITEBACK may force kswapd to sleep
> congested_wait(), PGDAT_DIRTY may force kswapd to writeback filesystem
> pages. But the worst here is PGDAT_CONGESTED, since it may force all
> direct reclaims to stall in wait_iff_congested(). Note that only kswapd
> have powers to clear any of these bits. This might just never happen if
> cgroup limits configured that way. So all direct reclaims will stall
> as long as we have some congested bdi in the system.
>
> Leave all pgdat->flags manipulations to kswapd. kswapd scans the whole
> pgdat, only kswapd can clear pgdat->flags once node is balance, thus
> it's reasonable to leave all decisions about node state to kswapd.
>
> Moving pgdat->flags manipulation to kswapd, means that cgroup2 recalim
> now loses its congestion throttling mechanism. Add per-cgroup congestion
> state and throttle cgroup2 reclaimers if memcg is in congestion state.
>
> Currently there is no need in per-cgroup PGDAT_WRITEBACK and PGDAT_DIRTY
> bits since they alter only kswapd behavior.
>
> The problem could be easily demonstrated by creating heavy congestion
> in one cgroup:
>
> echo "+memory" > /sys/fs/cgroup/cgroup.subtree_control
> mkdir -p /sys/fs/cgroup/congester
> echo 512M > /sys/fs/cgroup/congester/memory.max
> echo $$ > /sys/fs/cgroup/congester/cgroup.procs
> /* generate a lot of diry data on slow HDD */
> while true; do dd if=/dev/zero of=/mnt/sdb/zeroes bs=1M count=1024; done &
> ....
> while true; do dd if=/dev/zero of=/mnt/sdb/zeroes bs=1M count=1024; done &
>
> and some job in another cgroup:
>
> mkdir /sys/fs/cgroup/victim
> echo 128M > /sys/fs/cgroup/victim/memory.max
>
> # time cat /dev/sda > /dev/null
> real 10m15.054s
> user 0m0.487s
> sys 1m8.505s
>
> According to the tracepoint in wait_iff_congested(), the 'cat' spent 50%
> of the time sleeping there.
>
> With the patch, cat don't waste time anymore:
>
> # time cat /dev/sda > /dev/null
> real 5m32.911s
> user 0m0.411s
> sys 0m56.664s
>
Reviewers, please?
next prev parent reply other threads:[~2018-04-05 22:18 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-03-23 15:20 [PATCH v2 0/4] vmscan per-cgroup reclaim fixes Andrey Ryabinin
2018-03-23 15:20 ` [PATCH v2 1/4] mm/vmscan: Update stale comments Andrey Ryabinin
2018-04-06 16:08 ` Johannes Weiner
2018-03-23 15:20 ` [PATCH v2 2/4] mm/vmscan: remove redundant current_may_throttle() check Andrey Ryabinin
2018-04-06 16:10 ` Johannes Weiner
2018-03-23 15:20 ` [PATCH v2 3/4] mm/vmscan: Don't change pgdat state on base of a single LRU list state Andrey Ryabinin
2018-04-05 22:17 ` Andrew Morton
2018-04-06 1:04 ` Shakeel Butt
2018-04-06 16:28 ` Johannes Weiner
2018-04-06 17:25 ` Andrey Ryabinin
2018-03-23 15:20 ` [PATCH v2 4/4] mm/vmscan: Don't mess with pgdat->flags in memcg reclaim Andrey Ryabinin
2018-04-05 22:18 ` Andrew Morton [this message]
2018-04-06 2:13 ` Shakeel Butt
2018-04-06 11:44 ` Andrey Ryabinin
2018-04-06 14:15 ` Shakeel Butt
2018-04-06 13:52 ` [PATCH] mm-vmscan-dont-mess-with-pgdat-flags-in-memcg-reclaim-v2-fix Andrey Ryabinin
2018-04-06 14:37 ` Shakeel Butt
2018-04-06 15:09 ` Andrey Ryabinin
2018-04-06 15:22 ` Shakeel Butt
2018-04-06 16:36 ` Johannes Weiner
2018-04-06 18:02 ` [PATCH v3 1/2] mm/vmscan: don't change pgdat state on base of a single LRU list state Andrey Ryabinin
2018-04-06 18:02 ` [PATCH v3 2/2] mm/vmscan: don't mess with pgdat->flags in memcg reclaim Andrey Ryabinin
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=20180405151828.98b5bfb143a7a8b7dec4b153@linux-foundation.org \
--to=akpm@linux-foundation.org \
--cc=aryabinin@virtuozzo.com \
--cc=cgroups@vger.kernel.org \
--cc=hannes@cmpxchg.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=mgorman@techsingularity.net \
--cc=mhocko@kernel.org \
--cc=rostedt@goodmis.org \
--cc=shakeelb@google.com \
--cc=tj@kernel.org \
/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;
as well as URLs for NNTP newsgroup(s).