linux-kernel - Re: [PATCH v2 3/7] mm/compaction: correctly return failure with bogus compound

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Message-ID: <20230829093909.4hpria3qtouvdv6a@techsingularity.net>
Date:   Tue, 29 Aug 2023 10:39:09 +0100
From:   Mel Gorman <mgorman@...hsingularity.net>
To:     Kemeng Shi <shikemeng@...weicloud.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        akpm@...ux-foundation.org, baolin.wang@...ux.alibaba.com,
        david@...hat.com, willy@...radead.org
Subject: Re: [PATCH v2 3/7] mm/compaction: correctly return failure with
 bogus compound_order in strict mode

On Sat, Aug 26, 2023 at 11:36:13PM +0800, Kemeng Shi wrote:
> In strict mode, we should return 0 if there is any hole in pageblock. If
> we successfully isolated pages at beginning at pageblock and then have a
> bogus compound_order outside pageblock in next page. We will abort search
> loop with blockpfn > end_pfn. Although we will limit blockpfn to end_pfn,
> we will treat it as a successful isolation in strict mode as blockpfn is
> not < end_pfn and return partial isolated pages. Then
> isolate_freepages_range may success unexpectly with hole in isolated
> range.
> 
> Fixes: 9fcd6d2e052ee ("mm, compaction: skip compound pages by order in free scanner")
> Signed-off-by: Kemeng Shi <shikemeng@...weicloud.com>

Modify the (likely(order <= MAX_ORDER)) block to avoid ever updating
blockpfn past the end of the pageblock. Then remove the second redundant
check.

-- 
Mel Gorman
SUSE Labs