On Mon 15-10-12 10:25:14, KOSAKI Motohiro wrote: > > diff --git a/Documentation/sysctl/vm.txt b/Documentation/sysctl/vm.txt > > index 078701f..308fd77 100644 > > --- a/Documentation/sysctl/vm.txt > > +++ b/Documentation/sysctl/vm.txt > > @@ -640,6 +640,9 @@ swappiness > > This control is used to define how aggressive the kernel will swap > > memory pages. Higher values will increase agressiveness, lower values > > decrease the amount of swap. > > +The value can be used from the [0, 100] range, where 0 means no swapping > > +at all (even if there is a swap storage enabled) while 100 means that > > +anonymous pages are reclaimed in the same rate as file pages. > > I think this only correct when memcg. Even if swappiness==0, global reclaim swap > out anon pages before oom. Right you are (we really do swap when the file pages are really low)! Sorry about the confusion. I kind of became if(global_reclaim) block blind... Then this really needs a memcg specific documentation fix. What about the following? --- >From 59a60705abd2faf9e266a4270bbf302001845588 Mon Sep 17 00:00:00 2001 From: Michal Hocko <mhocko@xxxxxxx> Date: Mon, 15 Oct 2012 11:43:56 +0200 Subject: [PATCH] doc: describe memcg swappiness more precisely since fe35004f (mm: avoid swapping out with swappiness==0) memcg reclaim stopped swapping out anon pages completely when 0 value is used. Although this is somehow expected it hasn't been done for a really long time this way and so it is probably better to be explicit about the effect. Moreover global reclaim swapps out even when swappiness is 0 to prevent from OOM killer. Signed-off-by: Michal Hocko <mhocko@xxxxxxx> --- Documentation/cgroups/memory.txt | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/Documentation/cgroups/memory.txt b/Documentation/cgroups/memory.txt index c07f7b4..71c4da4 100644 --- a/Documentation/cgroups/memory.txt +++ b/Documentation/cgroups/memory.txt @@ -466,6 +466,10 @@ Note: 5.3 swappiness Similar to /proc/sys/vm/swappiness, but affecting a hierarchy of groups only. +Please note that unlike the global swappiness, memcg knob set to 0 +really prevents from any swapping even if there is a swap storage +available. This might lead to memcg OOM killer if there are no file +pages to reclaim. Following cgroups' swappiness can't be changed. - root cgroup (uses /proc/sys/vm/swappiness). -- 1.7.10.4 -- Michal Hocko SUSE Labs -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>