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Re: [PATCH v2 03/18] mm, page_alloc: don't retry initial attempt in slowpath

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On 06/01/2016 03:26 PM, Michal Hocko wrote:
> On Tue 31-05-16 15:08:03, Vlastimil Babka wrote:
> [...]
>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>> index da3a62a94b4a..9f83259a18a8 100644
>> --- a/mm/page_alloc.c
>> +++ b/mm/page_alloc.c
>> @@ -3367,10 +3367,9 @@ __alloc_pages_direct_reclaim(gfp_t gfp_mask, unsigned int order,
>>  	bool drained = false;
>>  
>>  	*did_some_progress = __perform_reclaim(gfp_mask, order, ac);
>> -	if (unlikely(!(*did_some_progress)))
>> -		return NULL;
>>  
>>  retry:
>> +	/* We attempt even when no progress, as kswapd might have done some */
>>  	page = get_page_from_freelist(gfp_mask, order, alloc_flags, ac);
> 
> Is this really likely to happen, though? Sure we might have last few
> reclaimable pages on the LRU lists but I am not sure this would make a
> large difference then.
> 
> That being said, I do not think this is harmful but I find it a bit
> weird to invoke a reclaim and then ignore the feedback... Will leave the
> decision up to you but the original patch seemed neater.

OK, I'll think about it.

>>  
>>  	/*
>> @@ -3378,7 +3377,7 @@ __alloc_pages_direct_reclaim(gfp_t gfp_mask, unsigned int order,
>>  	 * pages are pinned on the per-cpu lists or in high alloc reserves.
>>  	 * Shrink them them and try again
>>  	 */
>> -	if (!page && !drained) {
>> +	if (!page && *did_some_progress && !drained) {
>>  		unreserve_highatomic_pageblock(ac);
>>  		drain_all_pages(NULL);
>>  		drained = true;
> 
> I do not remember this in the previous version.

Because it's consequence of the new hunk above.

> Why shouldn't we
> unreserve highatomic reserves when there was no progress?

Previously the "return NULL" for no progress would also skip this. So I
wanted to change just the get_page_from_freelist() part. IIUC the
reasoning here is that if there was reclaim progress but we didn't
succeed getting the page, it can mean it's stuck on per-cpu or reserve.
If there was no progress, it's unlikely that anything is stuck there.

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[PATCH v2 00/18] make direct compaction more deterministic Vlastimil Babka <vbabka@suse.cz> - 2016-05-31 15:10 +0200
  [PATCH v2 02/18] mm, page_alloc: set alloc_flags only once in slowpath Vlastimil Babka <vbabka@suse.cz> - 2016-05-31 15:10 +0200
  [PATCH v2 15/18] mm, compaction: use proper alloc_flags in __compaction_suitable() Vlastimil Babka <vbabka@suse.cz> - 2016-05-31 15:10 +0200
  [PATCH v2 14/18] mm, compaction: create compact_gap wrapper Vlastimil Babka <vbabka@suse.cz> - 2016-05-31 15:10 +0200
    Re: [PATCH v2 14/18] mm, compaction: create compact_gap wrapper Michal Hocko <mhocko@kernel.org> - 2016-06-01 16:10 +0200
  [PATCH v2 17/18] mm, vmscan: make compaction_ready() more accurate and readable Vlastimil Babka <vbabka@suse.cz> - 2016-05-31 15:10 +0200
    Re: [PATCH v2 17/18] mm, vmscan: make compaction_ready() more  accurate and readable Michal Hocko <mhocko@kernel.org> - 2016-06-01 16:20 +0200
  [PATCH v2 04/18] mm, page_alloc: restructure direct compaction handling in slowpath Vlastimil Babka <vbabka@suse.cz> - 2016-05-31 15:20 +0200
  [PATCH v2 03/18] mm, page_alloc: don't retry initial attempt in slowpath Vlastimil Babka <vbabka@suse.cz> - 2016-05-31 15:20 +0200
    Re: [PATCH v2 03/18] mm, page_alloc: don't retry initial attempt in  slowpath Michal Hocko <mhocko@kernel.org> - 2016-06-01 15:30 +0200
      Re: [PATCH v2 03/18] mm, page_alloc: don't retry initial attempt in  slowpath Vlastimil Babka <vbabka@suse.cz> - 2016-06-01 17:00 +0200
  [PATCH v2 05/18] mm, page_alloc: make THP-specific decisions more generic Vlastimil Babka <vbabka@suse.cz> - 2016-05-31 15:20 +0200
  [PATCH v2 13/18] mm, compaction: use correct watermark when checking allocation success Vlastimil Babka <vbabka@suse.cz> - 2016-05-31 15:20 +0200
    Re: [PATCH v2 13/18] mm, compaction: use correct watermark when  checking allocation success Michal Hocko <mhocko@kernel.org> - 2016-06-01 16:00 +0200
  [PATCH v2 06/18] mm, thp: remove __GFP_NORETRY from khugepaged and madvised allocations Vlastimil Babka <vbabka@suse.cz> - 2016-05-31 15:20 +0200
    Re: [PATCH v2 06/18] mm, thp: remove __GFP_NORETRY from khugepaged  and madvised allocations Michal Hocko <mhocko@kernel.org> - 2016-06-01 15:40 +0200
  [PATCH v2 12/18] mm, compaction: more reliably increase direct compaction priority Vlastimil Babka <vbabka@suse.cz> - 2016-05-31 15:20 +0200
    Re: [PATCH v2 12/18] mm, compaction: more reliably increase direct  compaction priority Michal Hocko <mhocko@kernel.org> - 2016-06-01 16:00 +0200
  [PATCH v2 11/18] mm, compaction: add the ultimate direct compaction priority Vlastimil Babka <vbabka@suse.cz> - 2016-05-31 15:20 +0200
  [PATCH v2 10/18] mm, compaction: cleanup unused functions Vlastimil Babka <vbabka@suse.cz> - 2016-05-31 15:20 +0200
    Re: [PATCH v2 10/18] mm, compaction: cleanup unused functions Michal Hocko <mhocko@kernel.org> - 2016-06-01 15:50 +0200
  [PATCH v2 01/18] mm, compaction: don't isolate PageWriteback pages in MIGRATE_SYNC_LIGHT mode Vlastimil Babka <vbabka@suse.cz> - 2016-05-31 15:20 +0200
  [PATCH v2 09/18] mm, compaction: make whole_zone flag ignore cached scanner positions Vlastimil Babka <vbabka@suse.cz> - 2016-05-31 15:20 +0200
  [PATCH v2 18/18] mm, vmscan: use proper classzone_idx in should_continue_reclaim() Vlastimil Babka <vbabka@suse.cz> - 2016-05-31 15:20 +0200
    Re: [PATCH v2 18/18] mm, vmscan: use proper classzone_idx in  should_continue_reclaim() Michal Hocko <mhocko@kernel.org> - 2016-06-01 16:30 +0200
      Re: [PATCH v2 18/18] mm, vmscan: use proper classzone_idx in  should_continue_reclaim() Vlastimil Babka <vbabka@suse.cz> - 2016-06-01 17:20 +0200
        Re: [PATCH v2 18/18] mm, vmscan: use proper classzone_idx in  should_continue_reclaim() Michal Hocko <mhocko@kernel.org> - 2016-06-01 17:50 +0200
  [PATCH v2 08/18] mm, compaction: simplify contended compaction handling Vlastimil Babka <vbabka@suse.cz> - 2016-05-31 15:20 +0200
  [PATCH v2 16/18] mm, compaction: require only min watermarks for non-costly orders Vlastimil Babka <vbabka@suse.cz> - 2016-05-31 15:20 +0200
    Re: [PATCH v2 16/18] mm, compaction: require only min watermarks for  non-costly orders Michal Hocko <mhocko@kernel.org> - 2016-06-01 16:10 +0200
  [PATCH v2 07/18] mm, compaction: introduce direct compaction priority Vlastimil Babka <vbabka@suse.cz> - 2016-05-31 15:20 +0200

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