linux-kernel.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Roman Gushchin <guro@fb.com>
To: Dennis Zhou <dennis@kernel.org>
Cc: Tejun Heo <tj@kernel.org>, Christoph Lameter <cl@linux.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Vlastimil Babka <vbabka@suse.cz>, <linux-mm@kvack.org>,
	<linux-kernel@vger.kernel.org>, Roman Gushchin <guro@fb.com>
Subject: [PATCH v3 0/6] percpu: partial chunk depopulation
Date: Wed, 7 Apr 2021 20:57:30 -0700	[thread overview]
Message-ID: <20210408035736.883861-1-guro@fb.com> (raw)

In our production experience the percpu memory allocator is sometimes struggling
with returning the memory to the system. A typical example is a creation of
several thousands memory cgroups (each has several chunks of the percpu data
used for vmstats, vmevents, ref counters etc). Deletion and complete releasing
of these cgroups doesn't always lead to a shrinkage of the percpu memory,
so that sometimes there are several GB's of memory wasted.

The underlying problem is the fragmentation: to release an underlying chunk
all percpu allocations should be released first. The percpu allocator tends
to top up chunks to improve the utilization. It means new small-ish allocations
(e.g. percpu ref counters) are placed onto almost filled old-ish chunks,
effectively pinning them in memory.

This patchset solves this problem by implementing a partial depopulation
of percpu chunks: chunks with many empty pages are being asynchronously
depopulated and the pages are returned to the system.

To illustrate the problem the following script can be used:

--
#!/bin/bash

cd /sys/fs/cgroup

mkdir percpu_test
echo "+memory" > percpu_test/cgroup.subtree_control

cat /proc/meminfo | grep Percpu

for i in `seq 1 1000`; do
    mkdir percpu_test/cg_"${i}"
    for j in `seq 1 10`; do
	mkdir percpu_test/cg_"${i}"_"${j}"
    done
done

cat /proc/meminfo | grep Percpu

for i in `seq 1 1000`; do
    for j in `seq 1 10`; do
	rmdir percpu_test/cg_"${i}"_"${j}"
    done
done

sleep 10

cat /proc/meminfo | grep Percpu

for i in `seq 1 1000`; do
    rmdir percpu_test/cg_"${i}"
done

rmdir percpu_test
--

It creates 11000 memory cgroups and removes every 10 out of 11.
It prints the initial size of the percpu memory, the size after
creating all cgroups and the size after deleting most of them.

Results:
  vanilla:
    ./percpu_test.sh
    Percpu:             7488 kB
    Percpu:           481152 kB
    Percpu:           481152 kB

  with this patchset applied:
    ./percpu_test.sh
    Percpu:             7488 kB
    Percpu:           481408 kB
    Percpu:           135552 kB

So the total size of the percpu memory was reduced by more than 3.5 times.

v3:
  - introduced pcpu_check_chunk_hint()
  - fixed a bug related to the hint check
  - minor cosmetic changes
  - s/pretends/fixes (cc Vlastimil)

v2:
  - depopulated chunks are sidelined
  - depopulation happens in the reverse order
  - depopulate list made per-chunk type
  - better results due to better heuristics

v1:
  - depopulation heuristics changed and optimized
  - chunks are put into a separate list, depopulation scan this list
  - chunk->isolated is introduced, chunk->depopulate is dropped
  - rearranged patches a bit
  - fixed a panic discovered by krobot
  - made pcpu_nr_empty_pop_pages per chunk type
  - minor fixes

rfc:
  https://lwn.net/Articles/850508/


Roman Gushchin (6):
  percpu: fix a comment about the chunks ordering
  percpu: split __pcpu_balance_workfn()
  percpu: make pcpu_nr_empty_pop_pages per chunk type
  percpu: generalize pcpu_balance_populated()
  percpu: factor out pcpu_check_chunk_hint()
  percpu: implement partial chunk depopulation

 mm/percpu-internal.h |   4 +-
 mm/percpu-stats.c    |   9 +-
 mm/percpu.c          | 306 +++++++++++++++++++++++++++++++++++--------
 3 files changed, 261 insertions(+), 58 deletions(-)

-- 
2.30.2


             reply	other threads:[~2021-04-08  3:58 UTC|newest]

Thread overview: 26+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-04-08  3:57 Roman Gushchin [this message]
2021-04-08  3:57 ` [PATCH v3 1/6] percpu: fix a comment about the chunks ordering Roman Gushchin
2021-04-16 21:06   ` Dennis Zhou
2021-04-08  3:57 ` [PATCH v3 2/6] percpu: split __pcpu_balance_workfn() Roman Gushchin
2021-04-16 21:06   ` Dennis Zhou
2021-04-08  3:57 ` [PATCH v3 3/6] percpu: make pcpu_nr_empty_pop_pages per chunk type Roman Gushchin
2021-04-16 21:08   ` Dennis Zhou
2021-04-08  3:57 ` [PATCH v3 4/6] percpu: generalize pcpu_balance_populated() Roman Gushchin
2021-04-16 21:09   ` Dennis Zhou
2021-04-08  3:57 ` [PATCH v3 5/6] percpu: factor out pcpu_check_chunk_hint() Roman Gushchin
2021-04-16 21:15   ` Dennis Zhou
2021-04-08  3:57 ` [PATCH v3 6/6] percpu: implement partial chunk depopulation Roman Gushchin
2021-04-16 12:56 ` [PATCH v3 0/6] percpu: " Pratik Sampat
2021-04-16 14:18   ` Dennis Zhou
2021-04-16 15:28     ` Pratik Sampat
2021-04-16 17:13       ` Roman Gushchin
2021-04-16 18:27         ` Pratik Sampat
2021-04-16 18:34           ` Roman Gushchin
2021-04-16 18:41             ` Pratik Sampat
2021-04-16 19:09               ` Roman Gushchin
2021-04-16 19:44                 ` Pratik Sampat
2021-04-16 20:03                   ` Roman Gushchin
2021-04-17  7:08                     ` Pratik Sampat
2021-04-16 21:47                   ` Dennis Zhou
2021-04-17  7:14                     ` Pratik Sampat
2021-04-16 16:21     ` Roman Gushchin

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=20210408035736.883861-1-guro@fb.com \
    --to=guro@fb.com \
    --cc=akpm@linux-foundation.org \
    --cc=cl@linux.com \
    --cc=dennis@kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-mm@kvack.org \
    --cc=tj@kernel.org \
    --cc=vbabka@suse.cz \
    --subject='Re: [PATCH v3 0/6] percpu: partial chunk depopulation' \
    /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

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).