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SubjectRe: [RFC][PATCH 4/4] memcg: make oom less frequently
* 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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