Re: [PATCH 1/2] check the return value of soft_limit reclaim

[Ying Han <yinghan@google.com>]

On Sun, Mar 27, 2011 at 11:39 PM, KOSAKI Motohiro
<kosaki.motohiro@jp.fujitsu.com> wrote:
>> In the global background reclaim, we do soft reclaim before scanning the
>> per-zone LRU. However, the return value is ignored. This patch adds the logic
>> where no per-zone reclaim happens if the soft reclaim raise the free pages
>> above the zone's high_wmark.
>>
>> I did notice a similar check exists but instead leaving a "gap" above the
>> high_wmark(the code right after my change in vmscan.c). There are discussions
>> on whether or not removing the "gap" which intends to balance pressures across
>> zones over time. Without fully understand the logic behind, I didn't try to
>> merge them into one, but instead adding the condition only for memcg users
>> who care a lot on memory isolation.
>>
>> Signed-off-by: Ying Han <yinghan@google.com>
>
> Looks good to me. But this depend on "memcg soft limit" spec. To be honest,
> I don't know this return value ignorance is intentional or not. So I think
> you need to get ack from memcg folks.
>
>
>> ---
>>  mm/vmscan.c |   16 +++++++++++++++-
>>  1 files changed, 15 insertions(+), 1 deletions(-)
>>
>> diff --git a/mm/vmscan.c b/mm/vmscan.c
>> index 060e4c1..e4601c5 100644
>> --- a/mm/vmscan.c
>> +++ b/mm/vmscan.c
>> @@ -2320,6 +2320,7 @@ static unsigned long balance_pgdat(pg_data_t *pgdat, int order,
>>       int end_zone = 0;       /* Inclusive.  0 = ZONE_DMA */
>>       unsigned long total_scanned;
>>       struct reclaim_state *reclaim_state = current->reclaim_state;
>> +     unsigned long nr_soft_reclaimed;
>>       struct scan_control sc = {
>>               .gfp_mask = GFP_KERNEL,
>>               .may_unmap = 1,
>> @@ -2413,7 +2414,20 @@ loop_again:
>>                        * Call soft limit reclaim before calling shrink_zone.
>>                        * For now we ignore the return value
>>                        */
>> -                     mem_cgroup_soft_limit_reclaim(zone, order, sc.gfp_mask);
>> +                     nr_soft_reclaimed = mem_cgroup_soft_limit_reclaim(zone,
>> +                                                     order, sc.gfp_mask);
>> +
>> +                     /*
>> +                      * Check the watermark after the soft limit reclaim. If
>> +                      * the free pages is above the watermark, no need to
>> +                      * proceed to the zone reclaim.
>> +                      */
>> +                     if (nr_soft_reclaimed && zone_watermark_ok_safe(zone,
>> +                                     order, high_wmark_pages(zone),
>> +                                     end_zone, 0)) {
>> +                             __inc_zone_state(zone, NR_SKIP_RECLAIM_GLOBAL);
>
> NR_SKIP_RECLAIM_GLOBAL is defined by patch 2/2. please don't break bisectability.

Thanks and I will fix that.

--Ying
>
>
>
>> +                             continue;
>> +                     }
>>
>>                       /*
>>                        * We put equal pressure on every zone, unless
>> --
>> 1.7.3.1
>>
>
>
>
>

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