Messages in this thread | | | Date | Fri, 9 Jan 2009 14:33:43 +0530 | From | Balbir Singh <> | Subject | Re: [RFC][PATCH 4/4] memcg: make oom less frequently |
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* Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> [2009-01-09 17:52:15]:
> On Fri, 9 Jan 2009 11:28:04 +0530, Balbir Singh <balbir@linux.vnet.ibm.com> wrote: > > * Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> [2009-01-08 19:15:20]: > > > > > In previous implementation, mem_cgroup_try_charge checked the return > > > value of mem_cgroup_try_to_free_pages, and just retried if some pages > > > had been reclaimed. > > > But now, try_charge(and mem_cgroup_hierarchical_reclaim called from it) > > > only checks whether the usage is less than the limit. > > > > > > This patch tries to change the behavior as before to cause oom less frequently. > > > > > > To prevent try_charge from getting stuck in infinite loop, > > > MEM_CGROUP_RECLAIM_RETRIES_MAX is defined. > > > > > > > > > Signed-off-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> > > > --- > > > mm/memcontrol.c | 16 ++++++++++++---- > > > 1 files changed, 12 insertions(+), 4 deletions(-) > > > > > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > > > index 804c054..fedd76b 100644 > > > --- a/mm/memcontrol.c > > > +++ b/mm/memcontrol.c > > > @@ -42,6 +42,7 @@ > > > > > > struct cgroup_subsys mem_cgroup_subsys __read_mostly; > > > #define MEM_CGROUP_RECLAIM_RETRIES 5 > > > +#define MEM_CGROUP_RECLAIM_RETRIES_MAX 32 > > > > Why 32 are you seeing frequent OOMs? I had 5 iterations to allow > > > > 1. pages to move to swap cache, which added back pressure to memcg in > > the original implementation, since the pages came back > > 2. It look longer to move, recalim those pages. > > > > Ideally 3 would suffice, but I added an additional 2 retries for > > safety. > > > Before this patch, try_charge doesn't check the return value of > try_to_free_page, i.e. how many pages has been reclaimed, and > only checks whether the usage has become less than the limit. > So, oom can be caused if the group is too busy. > > IIRC memory-cgroup-hierarchical-reclaim patch introduced this behavior, > and, I don't remember in detail, some tests which had not caused oom > started to cause oom after it. > That was the motivation of my first version of this patch(*1). > > *1 http://lkml.org/lkml/2008/11/28/35 > > Anyway, this is the updated version. > I removed RETRIES_MAX. > > > Thanks, > Daisuke Nishimura. > === > From: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> > > In previous implementation, mem_cgroup_try_charge checked the return > value of mem_cgroup_try_to_free_pages, and just retried if some pages > had been reclaimed. > But now, try_charge(and mem_cgroup_hierarchical_reclaim called from it) > only checks whether the usage is less than the limit. > > This patch tries to change the behavior as before to cause oom less frequently. > > ChangeLog: RFC->v1 > - removed RETRIES_MAX. > > > Signed-off-by: Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> > --- > mm/memcontrol.c | 10 ++++++---- > 1 files changed, 6 insertions(+), 4 deletions(-) > > diff --git a/mm/memcontrol.c b/mm/memcontrol.c > index 7ba5c61..fb0e9eb 100644 > --- a/mm/memcontrol.c > +++ b/mm/memcontrol.c > @@ -781,10 +781,10 @@ static int mem_cgroup_hierarchical_reclaim(struct mem_cgroup *root_mem, > * but there might be left over accounting, even after children > * have left. > */ > - ret = try_to_free_mem_cgroup_pages(root_mem, gfp_mask, noswap, > + ret += try_to_free_mem_cgroup_pages(root_mem, gfp_mask, noswap, > get_swappiness(root_mem)); > if (mem_cgroup_check_under_limit(root_mem)) > - return 0; > + return 1; /* indicate reclaim has succeeded */ > if (!root_mem->use_hierarchy) > return ret; > > @@ -795,10 +795,10 @@ static int mem_cgroup_hierarchical_reclaim(struct mem_cgroup *root_mem, > next_mem = mem_cgroup_get_next_node(root_mem); > continue; > } > - ret = try_to_free_mem_cgroup_pages(next_mem, gfp_mask, noswap, > + ret += try_to_free_mem_cgroup_pages(next_mem, gfp_mask, noswap, > get_swappiness(next_mem)); > if (mem_cgroup_check_under_limit(root_mem)) > - return 0; > + return 1; /* indicate reclaim has succeeded */ > next_mem = mem_cgroup_get_next_node(root_mem); > } > return ret; > @@ -883,6 +883,8 @@ static int __mem_cgroup_try_charge(struct mm_struct *mm, > > ret = mem_cgroup_hierarchical_reclaim(mem_over_limit, gfp_mask, > noswap); > + if (ret) > + continue; > > /* > * try_to_free_mem_cgroup_pages() might not give us a full >
This makes sense
Acked-by: Balbir Singh <balbir@linux.vnet.ibm.com>
-- Balbir
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