Re: [PATCH 1/3] mm, reclaim: make should_continue_reclaim perform dryrun detection

[Mike Kravetz <mike.kravetz@oracle.com>]

On 8/5/19 3:57 AM, Vlastimil Babka wrote:
> On 8/5/19 10:42 AM, Vlastimil Babka wrote:
>> On 8/3/19 12:39 AM, Mike Kravetz wrote:
>>> From: Hillf Danton <hdanton@sina.com>
>>>
>>> Address the issue of should_continue_reclaim continuing true too often
>>> for __GFP_RETRY_MAYFAIL attempts when !nr_reclaimed and nr_scanned.
>>> This could happen during hugetlb page allocation causing stalls for
>>> minutes or hours.
>>>
>>> We can stop reclaiming pages if compaction reports it can make a progress.
>>> A code reshuffle is needed to do that.
>>
>>> And it has side-effects, however,
>>> with allocation latencies in other cases but that would come at the cost
>>> of potential premature reclaim which has consequences of itself.
>>
>> Based on Mel's longer explanation, can we clarify the wording here? e.g.:
>>
>> There might be side-effect for other high-order allocations that would
>> potentially benefit from more reclaim before compaction for them to be
>> faster and less likely to stall, but the consequences of
>> premature/over-reclaim are considered worse.
>>
>>> We can also bail out of reclaiming pages if we know that there are not
>>> enough inactive lru pages left to satisfy the costly allocation.
>>>
>>> We can give up reclaiming pages too if we see dryrun occur, with the
>>> certainty of plenty of inactive pages. IOW with dryrun detected, we are
>>> sure we have reclaimed as many pages as we could.
>>>
>>> Cc: Mike Kravetz <mike.kravetz@oracle.com>
>>> Cc: Mel Gorman <mgorman@suse.de>
>>> Cc: Michal Hocko <mhocko@kernel.org>
>>> Cc: Vlastimil Babka <vbabka@suse.cz>
>>> Cc: Johannes Weiner <hannes@cmpxchg.org>
>>> Signed-off-by: Hillf Danton <hdanton@sina.com>
>>> Tested-by: Mike Kravetz <mike.kravetz@oracle.com>
>>> Acked-by: Mel Gorman <mgorman@suse.de>
>>
>> Acked-by: Vlastimil Babka <vbabka@suse.cz>
>> I will send some followup cleanup.
> 
> How about this?
> ----8<----
> From 0040b32462587171ad22395a56699cc036ad483f Mon Sep 17 00:00:00 2001
> From: Vlastimil Babka <vbabka@suse.cz>
> Date: Mon, 5 Aug 2019 12:49:40 +0200
> Subject: [PATCH] mm, reclaim: cleanup should_continue_reclaim()
> 
> After commit "mm, reclaim: make should_continue_reclaim perform dryrun
> detection", closer look at the function shows, that nr_reclaimed == 0 means
> the function will always return false. And since non-zero nr_reclaimed implies
> non_zero nr_scanned, testing nr_scanned serves no purpose, and so does the
> testing for __GFP_RETRY_MAYFAIL.
> 
> This patch thus cleans up the function to test only !nr_reclaimed upfront, and
> remove the __GFP_RETRY_MAYFAIL test and nr_scanned parameter completely.
> Comment is also updated, explaining that approximating "full LRU list has been
> scanned" with nr_scanned == 0 didn't really work.
> 
> Signed-off-by: Vlastimil Babka <vbabka@suse.cz>

Acked-by: Mike Kravetz <mike.kravetz@oracle.com>

Would you like me to add this to the series, or do you want to send later?
-- 
Mike Kravetz