vfs_cache_min_ratio is a sysctl ported from PSBM-6. It supposed to increase performance, but it was noticed to do the opposite https://jira.sw.ru/browse/PSBM-68644.
It supposed to protect slabs from reclaiming if their percentage is lower than the sysctl value (2% by default). However, it's not quite clear in what scenario it supposed to improve performance. Moreover, I don't quite understand how is this 2% protection supposed to change anything in reclaim logic. If we have relatively small number of reclaimable slab objects they won't be reclaimed anyway because of priority protection. The following simple test: #!/bin/bash mkdir -p /vz/tst/ mkdir -p /sys/fs/cgroup/memory/tst for i in {1..4} ; do mkdir -p /sys/fs/cgroup/memory/tst/test$i # 1G echo $((1024*1024*1024)) > /sys/fs/cgroup/memory/tst/test$i/memory.limit_in_bytes echo $$ > /sys/fs/cgroup/memory/tst/test$i/tasks mkdir -p /vz/tst/test$i #fill slab_reclaimable stat /vz/tst/test$i > /dev/null for j in {1..10065} ; do mkdir -p /vz/tst/test$i/test$j stat /vz/tst/test$i/test$j > /dev/null done #read 1G file to fill page cache in memcg. cat /vz/test$i > /dev/null done cat /sys/fs/cgroup/memory/tst/memory.stat echo $$ > /sys/fs/cgroup/memory/tasks #create memory pressure, sizeof /vz/fill_ram #should be bigger than total ram. cat /vz/fill_ram > /dev/null show that there is no much difference between 0 and 2% settings. In both cases we prefer to reclaim page cache. So let's set vfs_cache_min_ratio to 0 and see how it goes. https://jira.sw.ru/browse/PSBM-69672 Signed-off-by: Andrey Ryabinin <aryabi...@virtuozzo.com> --- fs/dcache.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/fs/dcache.c b/fs/dcache.c index 2cb018a05078..ce8e24f22f9a 100644 --- a/fs/dcache.c +++ b/fs/dcache.c @@ -86,7 +86,7 @@ int sysctl_vfs_cache_pressure __read_mostly = 100; EXPORT_SYMBOL_GPL(sysctl_vfs_cache_pressure); -int sysctl_vfs_cache_min_ratio __read_mostly = 2; +int sysctl_vfs_cache_min_ratio __read_mostly = 0; __cacheline_aligned_in_smp DEFINE_SEQLOCK(rename_lock); -- 2.13.6 _______________________________________________ Devel mailing list Devel@openvz.org https://lists.openvz.org/mailman/listinfo/devel