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Subject: Re: [PATCH v2 3/7] mm/compaction: correctly return failure with bogus
 compound_order in strict mode
To:     Mel Gorman <mgorman@techsingularity.net>
Cc:     linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        akpm@linux-foundation.org, baolin.wang@linux.alibaba.com,
        david@redhat.com, willy@infradead.org
References: <20230826153617.4019189-1-shikemeng@huaweicloud.com>
 <20230826153617.4019189-4-shikemeng@huaweicloud.com>
 <20230829093909.4hpria3qtouvdv6a@techsingularity.net>
From:   Kemeng Shi <shikemeng@huaweicloud.com>
Message-ID: <f95b565a-796c-8d97-566b-d7877c9c1006@huaweicloud.com>
Date:   Wed, 30 Aug 2023 14:50:58 +0800
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on 8/29/2023 5:39 PM, Mel Gorman wrote:
> 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@huaweicloud.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.
> 
Sure, I will improve this in next version.