Re: [PATCH] memcg: fix behavior of mem_cgroup_resize_limit()
From: Michal Hocko <hidden>
Date: 2011-07-26 13:12:50
On Tue 26-07-11 14:35:38, Daisuke Nishimura wrote:
On Mon, 25 Jul 2011 15:47:40 +0200 Michal Hocko [off-list ref] wrote:quoted
On Fri 22-07-11 11:17:03, Daisuke Nishimura wrote:quoted
commit:22a668d7 introduced "memsw_is_minimum" flag, which becomes true when mem_limit == memsw_limit. The flag is checked at the beginning of reclaim, and "noswap" is set if the flag is true, because using swap is meaningless in this case. This works well in most cases, but when we try to shrink mem_limit, which is the same as memsw_limit now, we might fail to shrink mem_limit because swap doesn't used. This patch fixes this behavior by: - check MEM_CGROUP_RECLAIM_SHRINK at the begining of reclaim - If it is set, don't set "noswap" flag even if memsw_is_minimum is true. Signed-off-by: Daisuke Nishimura <redacted> --- mm/memcontrol.c | 2 +- 1 files changed, 1 insertions(+), 1 deletions(-)diff --git a/mm/memcontrol.c b/mm/memcontrol.c index ce0d617..cf6bae8 100644 --- a/mm/memcontrol.c +++ b/mm/memcontrol.c@@ -1649,7 +1649,7 @@ static int mem_cgroup_hierarchical_reclaim(struct mem_cgroup *root_mem, excess = res_counter_soft_limit_excess(&root_mem->res) >> PAGE_SHIFT; /* If memsw_is_minimum==1, swap-out is of-no-use. */ - if (!check_soft && root_mem->memsw_is_minimum) + if (!check_soft && !shrink && root_mem->memsw_is_minimum)It took me a while until I understood how we can end up having both flags unset - because I saw them as complementary before. But this is the mem_cgroup_do_charge path that is affected. Btw. shouldn't we push that check into the loop. We could catch also memsw changes done (e.g. increased memsw limit in order to cope with the current workload) while we were reclaiming from a subgroup.hmm, we shouldn't enable swap if the caller set MEM_CGROUP_RECLAIM_SOFT. So, something like this ? I think it must be another patch anyway.
Yes, the separate patch is reasonable. I have mentioned it just because I was looking at the code. Sorry for not preparing it myself.
quoted hunk ↗ jump to hunk
---@@ -1640,7 +1640,7 @@ static int mem_cgroup_hierarchical_reclaim(struct mem_cgroup *root_m struct mem_cgroup *victim; int ret, total = 0; int loop = 0; - bool noswap = reclaim_options & MEM_CGROUP_RECLAIM_NOSWAP; + bool noswap; bool shrink = reclaim_options & MEM_CGROUP_RECLAIM_SHRINK; bool check_soft = reclaim_options & MEM_CGROUP_RECLAIM_SOFT; unsigned long excess;@@ -1648,11 +1648,15 @@ static int mem_cgroup_hierarchical_reclaim(struct mem_cgroup *root excess = res_counter_soft_limit_excess(&root_mem->res) >> PAGE_SHIFT; - /* If memsw_is_minimum==1, swap-out is of-no-use. */ - if (!check_soft && !shrink && root_mem->memsw_is_minimum) - noswap = true; - while (1) { + if (reclaim_options & MEM_CGROUP_RECLAIM_NOSWAP) + noswap = true; + /* If memsw_is_minimum==1, swap-out is of-no-use. */ + else if (!check_soft && !shrink && root_mem->memsw_is_minimum) + noswap = true; + else + noswap = false; + victim = mem_cgroup_select_victim(root_mem); if (victim == root_mem) { loop++;
Little hairy but I I do not have a better idea (making the first two condition one doesn't improve readability too much IMO). So here is my Acked-by: Michal Hocko <redacted> for the change if that matters. I would add a description like this: " memcg: Recheck noswap conditions during reclaim hierarchy reclaim Currently we are are checking whether it makes sense to swap before we start the reclaim loop. This, however, doesn't handle a case when admin tries to cope with the memory pressure by increasing the memsw.limit so we can start swapping. Let's be more dynamic and set noswap flag everytime we are about to reclaim from a group. " Thanks -- Michal Hocko SUSE Labs SUSE LINUX s.r.o. Lihovarska 1060/12 190 00 Praha 9 Czech Republic -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@kvack.org"> email@kvack.org </a>