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Message-ID: <2f2985f0-f1a7-f085-fd18-107f3fba9478@suse.cz>
Date: Wed, 13 Sep 2023 16:40:48 +0200
From: Vlastimil Babka <vbabka@...e.cz>
To: Johannes Weiner <hannes@...xchg.org>,
Andrew Morton <akpm@...ux-foundation.org>
Cc: Mel Gorman <mgorman@...hsingularity.net>,
Miaohe Lin <linmiaohe@...wei.com>,
Kefeng Wang <wangkefeng.wang@...wei.com>,
Zi Yan <ziy@...dia.com>, linux-mm@...ck.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/6] mm: page_alloc: fix move_freepages_block() range
error
On 9/11/23 21:41, Johannes Weiner wrote:
> When a block is partially outside the zone of the cursor page, the
> function cuts the range to the pivot page instead of the zone
> start. This can leave large parts of the block behind, which
> encourages incompatible page mixing down the line (ask for one type,
> get another), and thus long-term fragmentation.
>
> This triggers reliably on the first block in the DMA zone, whose
> start_pfn is 1. The block is stolen, but everything before the pivot
> page (which was often hundreds of pages) is left on the old list.
>
> Signed-off-by: Johannes Weiner <hannes@...xchg.org>
Reviewed-by: Vlastimil Babka <vbabka@...e.cz>
Note below:
> ---
> mm/page_alloc.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index f6f658c3d394..5bbe5f3be5ad 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -1652,7 +1652,7 @@ int move_freepages_block(struct zone *zone, struct page *page,
>
> /* Do not cross zone boundaries */
> if (!zone_spans_pfn(zone, start_pfn))
> - start_pfn = pfn;
> + start_pfn = zone->zone_start_pfn;
> if (!zone_spans_pfn(zone, end_pfn))
> return 0;
Culdn't we also adjust end_pfn to zone_end_pfn() so we don't just ignore the
last half-pageblock for no good reason? (or am I missing any?)
Also would stop treating end_pfn as inclusive here and in move_freepages(),
it's rather uncommon.
>
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