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SubjectRe: [BUGFIX][PATCH 1/4] memcg: fix limit estimation at reclaim for hugepage
On Fri, 28 Jan 2011 12:24:49 +0900
KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> 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>

This patch looks good to me, but some nitpicks.

> ---
> 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;
> +}
> +
> static inline bool res_counter_check_under_soft_limit(struct res_counter *cnt)
> {
> bool ret;
> Index: mmotm-0125/mm/memcontrol.c
> ===================================================================
> --- mmotm-0125.orig/mm/memcontrol.c
> +++ mmotm-0125/mm/memcontrol.c
> @@ -1111,6 +1111,22 @@ static bool mem_cgroup_check_under_limit
> return false;
> }
>
> +static s64 mem_cgroup_check_margin(struct mem_cgroup *mem)
> +{
> + s64 mem_margin;
> +
> + if (do_swap_account) {
> + s64 memsw_margin;
> +
> + mem_margin = res_counter_check_margin(&mem->res);
> + memsw_margin = res_counter_check_margin(&mem->memsw);
> + if (mem_margin > memsw_margin)
> + mem_margin = memsw_margin;
> + } else
> + mem_margin = res_counter_check_margin(&mem->res);
> + return mem_margin;
> +}
> +
How about

mem_margin = res_counter_check_margin(&mem->res);
if (do_swap_account)
memsw_margin = res_counter_check_margin(&mem->memsw);
else
memsw_margin = RESOURCE_MAX;
return min(mem_margin, memsw_margin);

?
I think using min() makes it more clear what this function does.

> static unsigned int get_swappiness(struct mem_cgroup *memcg)
> {
> struct cgroup *cgrp = memcg->css.cgroup;
> @@ -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;
>
> /*
>
checkpatch complains some whitespace warnings.


Thanks,
Daisuke Nishimura.


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