linux-kernel - Re: [PATCH] mm/page_alloc: reduce fallbacks to (MIGRATE_PCPTYPES

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Date:   Thu, 09 Feb 2023 02:02:34 +0000
From:   "Yajun Deng" <yajun.deng@...ux.dev>
To:     "Vlastimil Babka" <vbabka@...e.cz>,
        "Andrew Morton" <akpm@...ux-foundation.org>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        "Zi Yan" <ziy@...dia.com>,
        "Mel Gorman" <mgorman@...hsingularity.net>,
        "David Hildenbrand" <david@...hat.com>,
        "Mike Rapoport" <rppt@...ux.ibm.com>,
        "Oscar Salvador" <osalvador@...e.de>
Subject: Re: [PATCH] mm/page_alloc: reduce fallbacks to (MIGRATE_PCPTYPES
 - 1)

February 9, 2023 12:07 AM, "Vlastimil Babka" <vbabka@...e.cz> wrote:

> On 2/3/23 23:23, Andrew Morton wrote:
> 
>> On Fri, 3 Feb 2023 18:01:32 +0800 Yajun Deng <yajun.deng@...ux.dev> wrote:
>> 
>>> The commit 1dd214b8f21c ("mm: page_alloc: avoid merging non-fallbackable
>>> pageblocks with others") has removed MIGRATE_CMA and MIGRATE_ISOLATE from
>>> fallbacks list. so there is no need to add an element at the end of every
>>> type.
>>> 
>>> Reduce fallbacks to (MIGRATE_PCPTYPES - 1).
> 
> Acked-by: Vlastimil Babka <vbabka@...e.cz>
> 
>> Thanks. `git log' suggests who should be cc'ed when fixing things...
>> 
>>> --- a/mm/page_alloc.c
>>> +++ b/mm/page_alloc.c
>>> @@ -2603,10 +2603,10 @@ struct page *__rmqueue_smallest(struct zone *zone, unsigned int order,
>>> *
>>> * The other migratetypes do not have fallbacks.
>>> */
>>> -static int fallbacks[MIGRATE_TYPES][3] = {
>>> - [MIGRATE_UNMOVABLE] = { MIGRATE_RECLAIMABLE, MIGRATE_MOVABLE, MIGRATE_TYPES },
>>> - [MIGRATE_MOVABLE] = { MIGRATE_RECLAIMABLE, MIGRATE_UNMOVABLE, MIGRATE_TYPES },
>>> - [MIGRATE_RECLAIMABLE] = { MIGRATE_UNMOVABLE, MIGRATE_MOVABLE, MIGRATE_TYPES },
>>> +static int fallbacks[MIGRATE_TYPES][MIGRATE_PCPTYPES - 1] = {
> 
> Why not also reduce the first index size from [MIGRATE_TYPES] to
> [MIGRATE_PCPTYPES] ?
> 

I overlooked this. I'll do it in the next patch.

>>> + [MIGRATE_UNMOVABLE] = { MIGRATE_RECLAIMABLE, MIGRATE_MOVABLE },
>>> + [MIGRATE_MOVABLE] = { MIGRATE_RECLAIMABLE, MIGRATE_UNMOVABLE },
>>> + [MIGRATE_RECLAIMABLE] = { MIGRATE_UNMOVABLE, MIGRATE_MOVABLE },
>>> };
>>> 
>>> #ifdef CONFIG_CMA
>>> @@ -2865,11 +2865,8 @@ int find_suitable_fallback(struct free_area *area, unsigned int order,
>>> return -1;
>>> 
>>> *can_steal = false;
>>> - for (i = 0;; i++) {
>>> + for (i = 0; i < MIGRATE_PCPTYPES - 1 ; i++) {
>>> fallback_mt = fallbacks[migratetype][i];
>>> - if (fallback_mt == MIGRATE_TYPES)
>>> - break;
>>> -
>>> if (free_area_empty(area, fallback_mt))
>>> continue;
>>> 
>>> --
>>> 2.25.1