linux-kernel - Re: [PATCH 4/6] mm: page_alloc: fix move_freepages

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Message-ID: <20230914100339.3dhgvsc6aprb5bbx@techsingularity.net>
Date:   Thu, 14 Sep 2023 11:03:39 +0100
From:   Mel Gorman <mgorman@...hsingularity.net>
To:     Johannes Weiner <hannes@...xchg.org>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        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 Mon, Sep 11, 2023 at 03:41:45PM -0400, 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>

Oops

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

-- 
Mel Gorman
SUSE Labs