From: Johannes Weiner <hannes@cmpxchg.org>
To: Yafang Shao <laoar.shao@gmail.com>
Cc: akpm@linux-foundation.org, mhocko@kernel.org,
vdavydov.dev@gmail.com, linux-mm@kvack.org,
Chris Down <chris@chrisdown.name>, Roman Gushchin <guro@fb.com>,
stable@vger.kernel.org
Subject: Re: [PATCH] mm, memcg: fix wrong mem cgroup protection
Date: Fri, 24 Apr 2020 09:44:38 -0400 [thread overview]
Message-ID: <20200424134438.GA496852@cmpxchg.org> (raw)
In-Reply-To: <20200424131450.GA495720@cmpxchg.org>
On Fri, Apr 24, 2020 at 09:14:52AM -0400, Johannes Weiner wrote:
> However, mem_cgroup_protected() never expected anybody to look at the
> effective protection values when it indicated that the cgroup is above
> its protection. As a result, a query during limit reclaim may return
> stale protection values that were calculated by a previous reclaim
> cycle in which the cgroup did have siblings.
Btw, I think there is opportunity to make this a bit less error prone.
We have a mem_cgroup_protected() that returns yes or no, essentially,
but protection isn't a binary state anymore.
It's also been a bit iffy that it looks like a simple predicate
function, but it indeed needs to run procedurally for each cgroup in
order for the calculations throughout the tree to be correct.
It might be better to have a
mem_cgroup_calculate_protection()
that runs for every cgroup we visit and sets up the internal state;
then have more self-explanatory query functions on top of that:
mem_cgroup_below_min()
mem_cgroup_below_low()
mem_cgroup_protection()
What do you guys think?
diff --git a/mm/vmscan.c b/mm/vmscan.c
index e0f502b5fca6..dbd3f75d39b9 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2615,14 +2615,15 @@ static void shrink_node_memcgs(pg_data_t *pgdat, struct scan_control *sc)
unsigned long reclaimed;
unsigned long scanned;
- switch (mem_cgroup_protected(target_memcg, memcg)) {
- case MEMCG_PROT_MIN:
+ mem_cgroup_calculate_protection(target_memcg, memcg);
+
+ if (mem_cgroup_below_min(memcg)) {
/*
* Hard protection.
* If there is no reclaimable memory, OOM.
*/
continue;
- case MEMCG_PROT_LOW:
+ } else if (mem_cgroup_below_low(memcg)) {
/*
* Soft protection.
* Respect the protection only as long as
@@ -2634,16 +2635,6 @@ static void shrink_node_memcgs(pg_data_t *pgdat, struct scan_control *sc)
continue;
}
memcg_memory_event(memcg, MEMCG_LOW);
- break;
- case MEMCG_PROT_NONE:
- /*
- * All protection thresholds breached. We may
- * still choose to vary the scan pressure
- * applied based on by how much the cgroup in
- * question has exceeded its protection
- * thresholds (see get_scan_count).
- */
- break;
}
reclaimed = sc->nr_reclaimed;
next prev parent reply other threads:[~2020-04-24 13:44 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-23 6:16 [PATCH] mm, memcg: fix wrong mem cgroup protection Yafang Shao
2020-04-23 15:33 ` Chris Down
2020-04-23 21:13 ` Roman Gushchin
2020-04-24 0:32 ` Yafang Shao
2020-04-24 10:40 ` Michal Hocko
2020-04-24 10:57 ` Yafang Shao
2020-04-24 0:49 ` Yafang Shao
2020-04-24 12:18 ` Chris Down
2020-04-24 12:44 ` Yafang Shao
2020-04-24 13:05 ` Chris Down
2020-04-24 13:10 ` Yafang Shao
2020-04-23 21:06 ` Roman Gushchin
2020-04-24 0:29 ` Yafang Shao
2020-04-24 13:14 ` Johannes Weiner
2020-04-24 13:44 ` Johannes Weiner [this message]
2020-04-24 14:33 ` Michal Hocko
2020-04-24 16:08 ` Yafang Shao
2020-04-24 14:29 ` Michal Hocko
2020-04-24 15:10 ` Johannes Weiner
2020-04-24 16:21 ` Michal Hocko
2020-04-24 16:51 ` Johannes Weiner
2020-04-27 8:25 ` Michal Hocko
2020-04-27 8:37 ` Yafang Shao
2020-04-27 16:52 ` Johannes Weiner
2020-04-24 16:21 ` Roman Gushchin
2020-04-24 16:30 ` Yafang Shao
2020-04-24 16:00 ` Yafang Shao
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=20200424134438.GA496852@cmpxchg.org \
--to=hannes@cmpxchg.org \
--cc=akpm@linux-foundation.org \
--cc=chris@chrisdown.name \
--cc=guro@fb.com \
--cc=laoar.shao@gmail.com \
--cc=linux-mm@kvack.org \
--cc=mhocko@kernel.org \
--cc=stable@vger.kernel.org \
--cc=vdavydov.dev@gmail.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;
as well as URLs for NNTP newsgroup(s).