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SubjectRe: [patch 1/3] memcg: prevent endless loop when charging huge pages
On Mon, 31 Jan 2011 15:03:53 +0100
Johannes Weiner <hannes@cmpxchg.org> wrote:

> The charging code can encounter a charge size that is bigger than a
> regular page in two situations: one is a batched charge to fill the
> per-cpu stocks, the other is a huge page charge.
>
> This code is distributed over two functions, however, and only the
> outer one is aware of huge pages. In case the charging fails, the
> inner function will tell the outer function to retry if the charge
> size is bigger than regular pages--assuming batched charging is the
> only case. And the outer function will retry forever charging a huge
> page.
>
> This patch makes sure the inner function can distinguish between batch
> charging and a single huge page charge. It will only signal another
> attempt if batch charging failed, and go into regular reclaim when it
> is called on behalf of a huge page.
>
> Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>

Thank you very much.

Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>

> ---
> mm/memcontrol.c | 11 +++++++++--
> 1 files changed, 9 insertions(+), 2 deletions(-)
>
> diff --git a/mm/memcontrol.c b/mm/memcontrol.c
> index d572102..73ea323 100644
> --- a/mm/memcontrol.c
> +++ b/mm/memcontrol.c
> @@ -1837,8 +1837,15 @@ static int __mem_cgroup_do_charge(struct mem_cgroup *mem, gfp_t gfp_mask,
> flags |= MEM_CGROUP_RECLAIM_NOSWAP;
> } else
> mem_over_limit = mem_cgroup_from_res_counter(fail_res, res);
> -
> - if (csize > PAGE_SIZE) /* change csize and retry */
> + /*
> + * csize can be either a huge page (HPAGE_SIZE), a batch of
> + * regular pages (CHARGE_SIZE), or a single regular page
> + * (PAGE_SIZE).
> + *
> + * Never reclaim on behalf of optional batching, retry with a
> + * single page instead.
> + */
> + if (csize == CHARGE_SIZE)
> return CHARGE_RETRY;
>
> if (!(gfp_mask & __GFP_WAIT))
> --
> 1.7.3.5
>
>



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