Re: [PATCH] Revert "mm: vmscan: fix misused nr_reclaimed in shrink_mem_cgroup_zone()"

From: Hillf Danton
Date: Tue Apr 10 2012 - 11:16:34 EST


add lkml
On Tue, Apr 10, 2012 at 11:00 PM, Hillf Danton <dhillf@xxxxxxxxx> wrote:
> On Tue, Apr 10, 2012 at 3:42 AM, Ying Han <yinghan@xxxxxxxxxx> wrote:
>> This reverts commit c38446cc65e1f2b3eb8630c53943b94c4f65f670.
>>
>> Before the commit, the code makes senses to me but not after the commit. The
>> "nr_reclaimed" is the number of pages reclaimed by scanning through the memcg's
>> lru lists. The "nr_to_reclaim" is the target value for the whole function. For
>> example, we like to early break the reclaim if reclaimed 32 pages under direct
>> reclaim (not DEF_PRIORITY).
>>
>> After the reverted commit, the target "nr_to_reclaim" is decremented each time
>> by "nr_reclaimed" but we still use it to compare the "nr_reclaimed". It just
>> doesn't make sense to me...
>>
> I downloaded mm/vmscan.c from the next tree a couple minutes ago, and
> see
> Â Â Â Â Â Â Â Â.nr_to_reclaim = SWAP_CLUSTER_MAX,
> and
> Â Â Â Ânr_reclaimed = do_try_to_free_pages(zonelist, &sc, &shrink);
>
> in try_to_free_pages().
>
> I also see
> Â Â Â Â Â Â Â Âtotal_scanned += sc->nr_scanned;
> Â Â Â Â Â Â Â Âif (sc->nr_reclaimed >= sc->nr_to_reclaim)
> Â Â Â Â Â Â Â Â Â Â Â Âgoto out;
>
> in do_try_to_free_pages(),
>
> then would you please say a few words about the sense
> of the check of nr_to_reclaim?
>
>
>> Signed-off-by: Ying Han <yinghan@xxxxxxxxxx>
>> ---
>> Âmm/vmscan.c | Â Â7 +------
>> Â1 files changed, 1 insertions(+), 6 deletions(-)
>>
>> diff --git a/mm/vmscan.c b/mm/vmscan.c
>> index 33c332b..1a51868 100644
>> --- a/mm/vmscan.c
>> +++ b/mm/vmscan.c
>> @@ -2107,12 +2107,7 @@ restart:
>> Â Â Â Â Â Â Â Â * with multiple processes reclaiming pages, the total
>> Â Â Â Â Â Â Â Â * freeing target can get unreasonably large.
>> Â Â Â Â Â Â Â Â */
>> - Â Â Â Â Â Â Â if (nr_reclaimed >= nr_to_reclaim)
>> - Â Â Â Â Â Â Â Â Â Â Â nr_to_reclaim = 0;
>> - Â Â Â Â Â Â Â else
>> - Â Â Â Â Â Â Â Â Â Â Â nr_to_reclaim -= nr_reclaimed;
>> -
>> - Â Â Â Â Â Â Â if (!nr_to_reclaim && priority < DEF_PRIORITY)
>> + Â Â Â Â Â Â Â if (nr_reclaimed >= nr_to_reclaim && priority < DEF_PRIORITY)
>> Â Â Â Â Â Â Â Â Â Â Â Âbreak;
>> Â Â Â Â}
>> Â Â Â Âblk_finish_plug(&plug);
>> --
>> 1.7.7.3
>>
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