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SubjectRe: [BUGFIX][PATCH 1/4] memcg: fix limit estimation at reclaim for hugepage
On Fri, Jan 28, 2011 at 12:24:49PM +0900, KAMEZAWA Hiroyuki wrote:
> From: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
>
> Current memory cgroup's code tends to assume page_size == PAGE_SIZE
> and arrangement for THP is not enough yet.
>
> This is one of fixes for supporing THP. This adds
> mem_cgroup_check_margin() and checks whether there are required amount of
> free resource after memory reclaim. By this, THP page allocation
> can know whether it really succeeded or not and avoid infinite-loop
> and hangup.
>
> Total fixes for do_charge()/reclaim memory will follow this patch.
>
> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
> ---
> include/linux/res_counter.h | 11 +++++++++++
> mm/memcontrol.c | 25 ++++++++++++++++++++++++-
> 2 files changed, 35 insertions(+), 1 deletion(-)
>
> Index: mmotm-0125/include/linux/res_counter.h
> ===================================================================
> --- mmotm-0125.orig/include/linux/res_counter.h
> +++ mmotm-0125/include/linux/res_counter.h
> @@ -182,6 +182,17 @@ static inline bool res_counter_check_und
> return ret;
> }
>
> +static inline s64 res_counter_check_margin(struct res_counter *cnt)
> +{
> + s64 ret;
> + unsigned long flags;
> +
> + spin_lock_irqsave(&cnt->lock, flags);
> + ret = cnt->limit - cnt->usage;
> + spin_unlock_irqrestore(&cnt->lock, flags);
> + return ret;
> +}

This function does not check anything. You could name it
res_counter_get_margin() e.g. But if you do that, I will complain
that it's asymmetric to res_counter_check_under_limit(). And the
result will be pretty close to my version...

> @@ -1853,7 +1869,14 @@ static int __mem_cgroup_do_charge(struct
> * Check the limit again to see if the reclaim reduced the
> * current usage of the cgroup before giving up
> */
> - if (ret || mem_cgroup_check_under_limit(mem_over_limit))
> + if (mem_cgroup_check_margin(mem_over_limit) >= csize)
> + return CHARGE_RETRY;
> +
> + /*
> + * If the charge size is a PAGE_SIZE, it's not hopeless while
> + * we can reclaim a page.
> + */
> + if (csize == PAGE_SIZE && ret)
> return CHARGE_RETRY;

That makes sense.


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