Re: [PATCHv3] memcg: fix get_scan_count for small targets

[Ying Han]

Acked-by: Ying Han <yinghan@xxxxxxxxxx>

--Ying
On Wed, Apr 27, 2011 at 2:14 AM, Minchan Kim <minchan.kim@xxxxxxxxx> wrote:
> On Wed, Apr 27, 2011 at 5:48 PM, KAMEZAWA Hiroyuki
> <kamezawa.hiroyu@xxxxxxxxxxxxxx> wrote:
>> On Wed, 27 Apr 2011 17:48:18 +0900
>> Minchan Kim <minchan.kim@xxxxxxxxx> wrote:
>>
>>> On Wed, Apr 27, 2011 at 4:47 PM, KAMEZAWA Hiroyuki
>>> <kamezawa.hiroyu@xxxxxxxxxxxxxx> wrote:
>>> > At memory reclaim, we determine the number of pages to be scanned
>>> > per zone as
>>> >        (anon + file) >> priority.
>>> > Assume
>>> >        scan = (anon + file) >> priority.
>>> >
>>> > If scan < SWAP_CLUSTER_MAX, the scan will be skipped for this time
>>> > and priority gets higher. This has some problems.
>>> >
>>> >  1. This increases priority as 1 without any scan.
>>> >     To do scan in this priority, amount of pages should be larger than 512M.
>>> >     If pages>>priority < SWAP_CLUSTER_MAX, it's recorded and scan will be
>>> >     batched, later. (But we lose 1 priority.)
>>> >     If memory size is below 16M, pages >> priority is 0 and no scan in
>>> >     DEF_PRIORITY forever.
>>> >
>>> >  2. If zone->all_unreclaimabe==true, it's scanned only when priority==0.
>>> >     So, x86's ZONE_DMA will never be recoverred until the user of pages
>>> >     frees memory by itself.
>>> >
>>> >  3. With memcg, the limit of memory can be small. When using small memcg,
>>> >     it gets priority < DEF_PRIORITY-2 very easily and need to call
>>> >     wait_iff_congested().
>>> >     For doing scan before priorty=9, 64MB of memory should be used.
>>> >
>>> > Then, this patch tries to scan SWAP_CLUSTER_MAX of pages in force...when
>>> >
>>> >  1. the target is enough small.
>>> >  2. it's kswapd or memcg reclaim.
>>> >
>>> > Then we can avoid rapid priority drop and may be able to recover
>>> > all_unreclaimable in a small zones. And this patch removes nr_saved_scan.
>>> > This will allow scanning in this priority even when pages >> priority
>>> > is very small.
>>> >
>>> > Changelog v2->v3
>>> >  - removed nr_saved_scan completely.
>>> >
>>> > Signed-off-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
>>> Reviewed-by: Minchan Kim <minchan.kim@xxxxxxxxx>
>>>
>>> The patch looks good to me but I have a nitpick about just coding style.
>>> How about this? I think below looks better but it's just my private
>>> opinion and I can't insist on my style. If you don't mind it, ignore.
>>>
>>
>> I did this at the 1st try and got bug.....a variable 'file' here is
>> reused and now broken. Renaming it with new variable will be ok, but it
>
> Right you are. I missed that. :)
> Thanks.
>
>
> --
> Kind regards,
> Minchan Kim
>
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