Re: [PATCH V5 4/5] mm, vmscan: fix do_try_to_free_pages() livelock

[Ying Han <yinghan@google.com>]

On Tue, Jun 19, 2012 at 11:29 AM, KOSAKI Motohiro
<kosaki.motohiro@jp.fujitsu.com> wrote:
> On 6/18/2012 12:47 PM, Ying Han wrote:
>> Currently, do_try_to_free_pages() can enter livelock. Because of,
>> now vmscan has two conflicted policies.
>>
>> 1) kswapd sleep when it couldn't reclaim any page even though
>>    reach priority 0. This is because to avoid kswapd() infinite
>>    loop. That said, kswapd assume direct reclaim makes enough
>>    free pages either regular page reclaim or oom-killer.
>>    This logic makes kswapd -> direct-reclaim dependency.
>> 2) direct reclaim continue to reclaim without oom-killer until
>>    kswapd turn on zone->all_unreclaimble. This is because
>>    to avoid too early oom-kill.
>>    This logic makes direct-reclaim -> kswapd dependency.
>>
>> In worst case, direct-reclaim may continue to page reclaim forever
>> when kswapd is slept and any other thread don't wakeup kswapd.
>>
>> We can't turn on zone->all_unreclaimable because this is racy.
>> direct reclaim path don't take any lock. Thus this patch removes
>> zone->all_unreclaimable field completely and recalculates every
>> time.
>>
>> Note: we can't take the idea that direct-reclaim see zone->pages_scanned
>> directly and kswapd continue to use zone->all_unreclaimable. Because,
>> it is racy. commit 929bea7c71 (vmscan: all_unreclaimable() use
>> zone->all_unreclaimable as a name) describes the detail.
>>
>> Reported-by: Aaditya Kumar <aaditya.kumar.30@gmail.com>
>> Reported-by: Ying Han <yinghan@google.com>
>> Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
>> Acked-by: Rik van Riel <riel@redhat.com>
>
> Please drop this. I've got some review comment about this patch and
> i need respin. but thank you for paying attention this.

Thanks for the heads up. Are you working on the new version of it,
since I included this patch in my softlimit reclaim patchset as a
replacement of one patch i had.

--Ying
>
>
>

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