New subject: [PATCH OLK-5.10 1/3] mm/readahead: break read-ahead loop if filemap_add_folio return -ENOMEM

26 Mar 2024

      Recently, when install package in a docker which almost reached its memory
limit, the installer has no respond severely for more than 15 minutes.
During this period, I/O stays high(~1G/s) and influence the whole machine.
I've constructed a use case as follows:

  1. create a docker:

	$ cat test.sh
	#!/bin/bash

	docker rm centos7 --force

	docker create --name centos7 --memory 4G --memory-swap 6G centos:7 /usr/sbin/init
	docker start centos7
	sleep 1

	docker cp ./alloc_page centos7:/
	docker cp ./reproduce.sh centos7:/

	docker exec -it centos7 /bin/bash

  2. try reproduce the problem in docker:

	$ cat reproduce.sh
	#!/bin/bash

	while true; do
		flag=$(ps -ef | grep -v grep | grep alloc_page| wc -l)
		if [ "$flag" -eq 0 ]; then
			/alloc_page &
		fi

		sleep 30

		start_time=$(date +%s)
		yum install -y expect > /dev/null 2>&1

		end_time=$(date +%s)

		elapsed_time=$((end_time - start_time))

		echo "$elapsed_time seconds"
		yum remove -y expect > /dev/null 2>&1
	done

	$ cat alloc_page.c:
	#include <stdio.h>
	#include <stdlib.h>
	#include <unistd.h>
	#include <string.h>

	#define SIZE 1*1024*1024 //1M

	int main()
	{
		void *addr = NULL;
		int i;

		for (i = 0; i < 1024 * 6 - 50;i++) {
			addr = (void *)malloc(SIZE);
			if (!addr)
				return -1;

			memset(addr, 0, SIZE);
		}

		sleep(99999);
		return 0;
	}

We found that this problem is caused by a lot ot meaningless read-ahead.
Since the docker is almost met memory limit, the page will be reclaimed
immediately after read-ahead and will read-ahead again immediately.
The program is executed slowly and waste a lot of I/O resource.

These patches aim to break the read-ahead in above scenario.

Liu Shixin (3):
  mm/readahead: break read-ahead loop if filemap_add_folio return
    -ENOMEM
  mm/filemap: don't decrease mmap_miss when folio has workingset flag
  mm/readahead: add sysctl to enable early break readahead

 Documentation/admin-guide/sysctl/vm.rst |  7 +++++++
 include/linux/pagemap.h                 |  2 ++
 kernel/sysctl.c                         |  9 +++++++++
 mm/filemap.c                            | 14 +++++++++++++-
 mm/readahead.c                          | 20 +++++++++++++++-----
 5 files changed, 46 insertions(+), 6 deletions(-)

-- 
2.25.1

[PATCH OLK-5.10 0/3] Fix I/O high when memory almost met memcg limit

Liu Shixin

Liu Shixin

Liu Shixin

Liu Shixin

patchwork bot

tags

participants (2)