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