linux-kernel - Re: [PATCH] mm: page_alloc: remove stale CMA guard code

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Date:   Fri, 25 Aug 2023 10:40:39 +0100
From:   Mel Gorman <mgorman@...hsingularity.net>
To:     Johannes Weiner <hannes@...xchg.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        Vlastimil Babka <vbabka@...e.cz>,
        David Hildenbrand <david@...hat.com>,
        Miaohe Lin <linmiaohe@...wei.com>,
        Pavel Tatashin <pasha.tatashin@...een.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: page_alloc: remove stale CMA guard code

On Thu, Aug 24, 2023 at 11:38:21AM -0400, Johannes Weiner wrote:
> In the past, movable allocations could be disallowed from CMA through
> PF_MEMALLOC_PIN. As CMA pages are funneled through the MOVABLE
> pcplist, this required filtering that cornercase during allocations,
> such that pinnable allocations wouldn't accidentally get a CMA page.
> 
> However, since 8e3560d963d2 ("mm: honor PF_MEMALLOC_PIN for all
> movable pages"), PF_MEMALLOC_PIN automatically excludes
> __GFP_MOVABLE. Once again, MOVABLE implies CMA is allowed.
> 
> Remove the stale filtering code. Also remove a stale comment that was
> introduced as part of the filtering code, because the filtering let
> order-0 pages fall through to the buddy allocator. See 1d91df85f399
> ("mm/page_alloc: handle a missing case for
> memalloc_nocma_{save/restore} APIs") for context. The comment's been
> obsolete since the introduction of the explicit ALLOC_HIGHATOMIC flag
> in eb2e2b425c69 ("mm/page_alloc: explicitly record high-order atomic
> allocations in alloc_flags").
> 
> Signed-off-by: Johannes Weiner <hannes@...xchg.org>

Acked-by: Mel Gorman <mgorman@...hsingularity.net>

-- 
Mel Gorman
SUSE Labs