From: "Michal Koutný" <mkoutny@suse.com>
To: Roman Gushchin <roman.gushchin@linux.dev>
Cc: cgroups@vger.kernel.org, linux-mm@kvack.org,
linux-kernel@vger.kernel.org,
Richard Palethorpe <rpalethorpe@suse.com>,
Andrew Morton <akpm@linux-foundation.org>,
Shakeel Butt <shakeelb@google.com>,
Michal Hocko <mhocko@suse.com>, Vlastimil Babka <vbabka@suse.cz>,
"Matthew Wilcox (Oracle)" <willy@infradead.org>,
Muchun Song <songmuchun@bytedance.com>,
Johannes Weiner <hannes@cmpxchg.org>,
Yang Shi <shy828301@gmail.com>,
Suren Baghdasaryan <surenb@google.com>, Tejun Heo <tj@kernel.org>,
Chris Down <chris@chrisdown.name>
Subject: Re: [RFC PATCH] mm: memcg: Do not count memory.low reclaim if it does not happen
Date: Fri, 25 Mar 2022 11:31:18 +0100 [thread overview]
Message-ID: <20220325103118.GC2828@blackbody.suse.cz> (raw)
In-Reply-To: <5049EBC3-5BAE-4509-BA63-1F4A7D913517@linux.dev>
On Thu, Mar 24, 2022 at 11:17:14AM -0700, Roman Gushchin <roman.gushchin@linux.dev> wrote:
> Ok, so it’s not really about the implementation details of the reclaim
> mechanism (I mean rounding up to the batch size etc),
Actually, that was what I deemed more serious first.
It's the point 2 of RFCness:
| 2) The observed behavior slightly impacts distribution of parent's memory.low.
| Constructed example is a passive protected workload in s1 and active in s2
| (active ~ counteracts the reclaim with allocations). It could strip
| protection from s1 one by one (one:=SWAP_CLUSTER_MAX/2^sc.priority).
| That may be considered both wrong (s1 should have been more protected) or
| correct s2 deserves protection due to its activity.
| I don't have (didn't collect) data for this, so I think just masking the
| false events is sufficient (or independent).
> Idk, I don’t have a strong argument against this change (except that
> it changes the existing behavior), but I also don’t see why such
> events are harmful. Do you mind elaborating a bit more?
So I've collected some demo data now.
systemd-run \
-u precious.service --slice=test-protected.slice \
-p MemoryLow=50M \
/root/memeater 50 # allocates 50M anon, doesn't use it
systemd-run \
-u victim.service --slice=test-protected.slice \
-p MemoryLow=0M \
/root/memeater -m 50 50 # allocates 50M anon, uses it
echo "Started workloads"
systemctl set-property --runtime test.slice MemoryMax=200M
systemctl set-property --runtime test-protected.slice MemoryLow=50M
sleep 5
systemd-run \
-u pressure.service --slice=test.slice \
-p MemorySwapMax=0M \ # to push test-protected.slice to swap
/root/memeater -m 170 170
sleep 5
systemd-cgtop -b -1 -m test.slice
Result with memory_recursiveprot
> Control Group Tasks %CPU Memory Input/s Output/s
> test.slice 3 - 199.9M - -
> test.slice/pressure.service 1 - 170.5M - -
> test.slice/test-protected.slice 2 - 29.4M - -
> test.slice/test-protected.slice/victim.service 1 - 29.1M - -
> test.slice/test-protected.slice/precious.service 1 - 292.0K - -
Result without memory_recursiveprot
> Control Group Tasks %CPU Memory Input/s Output/s
> test.slice 3 - 199.8M - -
> test.slice/pressure.service 1 - 170.5M - -
> test.slice/test-protected.slice 2 - 29.3M - -
> test.slice/test-protected.slice/precious.service 1 - 28.7M - -
> test.slice/test-protected.slice/victim.service 1 - 560.0K - -
(kernel 5.17.0, systemd 249.10)
So with this result, I'd say the event reporting is an independent change
(admiteddly, thanks to the current implementation (not the proposal of
mine) I noticed this issue).
/me scratches head, let me review my other approaches...
Michal
prev parent reply other threads:[~2022-03-25 10:31 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-03-22 18:22 [RFC PATCH] mm: memcg: Do not count memory.low reclaim if it does not happen Michal Koutný
2022-03-23 21:44 ` Roman Gushchin
2022-03-24 9:51 ` Michal Koutný
2022-03-24 18:17 ` Roman Gushchin
2022-03-25 10:31 ` Michal Koutný [this message]
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