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Message-ID: <c243c9f4-51c9-797a-6ac2-b87d1689da14@linux.alibaba.com>
Date: Tue, 29 Aug 2023 11:27:43 +0800
From: Baolin Wang <baolin.wang@...ux.alibaba.com>
To: Kemeng Shi <shikemeng@...weicloud.com>, linux-mm@...ck.org,
linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
mgorman@...hsingularity.net, 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 8/26/2023 11:36 PM, 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>
LGTM.
Reviewed-by: Baolin Wang <baolin.wang@...ux.alibaba.com>
> ---
> mm/compaction.c | 11 +++++++++--
> 1 file changed, 9 insertions(+), 2 deletions(-)
>
> diff --git a/mm/compaction.c b/mm/compaction.c
> index a40550a33aee..b4d03c9ffe7c 100644
> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -631,6 +631,14 @@ static unsigned long isolate_freepages_block(struct compact_control *cc,
> page += (1UL << order) - 1;
> nr_scanned += (1UL << order) - 1;
> }
> + /*
> + * There is a tiny chance that we have read bogus
> + * compound_order(), so be careful to not go outside
> + * of the pageblock.
> + */
> + if (unlikely(blockpfn >= end_pfn))
> + blockpfn = end_pfn - 1;
> +
> goto isolate_fail;
> }
>
> @@ -678,8 +686,7 @@ static unsigned long isolate_freepages_block(struct compact_control *cc,
> spin_unlock_irqrestore(&cc->zone->lock, flags);
>
> /*
> - * There is a tiny chance that we have read bogus compound_order(),
> - * so be careful to not go outside of the pageblock.
> + * Be careful to not go outside of the pageblock.
> */
> if (unlikely(blockpfn > end_pfn))
> blockpfn = end_pfn;
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