linux-kernel - Re: [PATCH 06/10] mm: page_alloc: fix freelist movement during block conversion

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Date: Mon, 8 Apr 2024 09:24:35 +0200
From: Vlastimil Babka <vbabka@...e.cz>
To: Johannes Weiner <hannes@...xchg.org>,
 Baolin Wang <baolin.wang@...ux.alibaba.com>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
 Mel Gorman <mgorman@...hsingularity.net>, Zi Yan <ziy@...dia.com>,
 "Huang, Ying" <ying.huang@...el.com>, David Hildenbrand <david@...hat.com>,
 linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 06/10] mm: page_alloc: fix freelist movement during block
 conversion

On 4/5/24 6:56 PM, Johannes Weiner wrote:
> Hi Baolin,
> Ouch, sorry about that! I changed that specific part around later
> during development and didn't retest with CMA. I'll be sure to
> re-enable it again in my config.
> 
>> After making the following modifications, the regression is gone.
>> 
>> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
>> index ce67dc6777fa..a7cfe65e45c1 100644
>> --- a/mm/page_alloc.c
>> +++ b/mm/page_alloc.c
>> @@ -2139,7 +2139,8 @@ __rmqueue(struct zone *zone, unsigned int order, 
>> int migratetype,
>>          if (unlikely(!page)) {
>>                  if (alloc_flags & ALLOC_CMA)
>>                          page = __rmqueue_cma_fallback(zone, order);
>> -               else
>> +
>> +               if (!page)
>>                          page = __rmqueue_fallback(zone, order, migratetype,
>>                                                    alloc_flags);
>>          }
>> 
>> But I am not sure your original change is intentional? IIUC, we still 
>> need try fallbacking even though CMA allocation is failed, please 
>> correct me if I misunderstand your code. Thanks.
> 
> No, this was accidental. I missed that CMA dependency when changing
> things around for the new return type of __rmqueue_fallback(). Your
> fix is good: just because the request qualifies for CMA doesn't mean
> it will succeed from that region. We need the fallback for those.
> 
> Andrew, could you please pick up Baolin's change for this patch?
> 
> [baolin.wang@...ux.alibaba.com: fix allocation failures with CONFIG_CMA]
> 
> Thanks for debugging this and the fix, Baolin.

Good fix indeed, didn't spot the issue during review. Thanks!