linux-kernel - Re: [RFC PATCH v3 2/8] mm: compaction: handle non-lru compound pages properly in isolate_migratepages

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Message-ID: <71108865-5368-4725-AA5A-35A57C350D77@nvidia.com>
Date:   Thu, 13 Jan 2022 09:57:19 -0500
From:   Zi Yan <ziy@...dia.com>
To:     David Hildenbrand <david@...hat.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Michael Ellerman <mpe@...erman.id.au>,
        Christoph Hellwig <hch@....de>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Robin Murphy <robin.murphy@....com>,
        linuxppc-dev@...ts.ozlabs.org,
        virtualization@...ts.linux-foundation.org,
        iommu@...ts.linux-foundation.org, Vlastimil Babka <vbabka@...e.cz>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Eric Ren <renzhengeek@...il.com>
Subject: Re: [RFC PATCH v3 2/8] mm: compaction: handle non-lru compound pages properly in isolate_migratepages_block().

On 12 Jan 2022, at 6:01, David Hildenbrand wrote:

> On 05.01.22 22:47, Zi Yan wrote:
>> From: Zi Yan <ziy@...dia.com>
>>
>> In isolate_migratepages_block(), a !PageLRU tail page can be encountered
>> when the page is larger than a pageblock. Use compound head page for the
>> checks inside and skip the entire compound page when isolation succeeds.
>>
>
> This will currently never happen, due to the way we always isolate
> MAX_ORDER -1 ranges, correct?

You are right.

>
> Better note that in the patch description, because currently it reads
> like it's an actual fix "can be encountered".
>

Will do. This is a preparation patch for the upcoming commits.


>> Signed-off-by: Zi Yan <ziy@...dia.com>
>> ---
>>  mm/compaction.c | 10 +++++++---
>>  1 file changed, 7 insertions(+), 3 deletions(-)
>>
>> diff --git a/mm/compaction.c b/mm/compaction.c
>> index b4e94cda3019..ad9053fbbe06 100644
>> --- a/mm/compaction.c
>> +++ b/mm/compaction.c
>> @@ -979,19 +979,23 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
>>  		 * Skip any other type of page
>>  		 */
>>  		if (!PageLRU(page)) {
>> +			struct page *head = compound_head(page);
>>  			/*
>>  			 * __PageMovable can return false positive so we need
>>  			 * to verify it under page_lock.
>>  			 */
>> -			if (unlikely(__PageMovable(page)) &&
>> -					!PageIsolated(page)) {
>> +			if (unlikely(__PageMovable(head)) &&
>> +					!PageIsolated(head)) {
>>  				if (locked) {
>>  					unlock_page_lruvec_irqrestore(locked, flags);
>>  					locked = NULL;
>>  				}
>>
>> -				if (!isolate_movable_page(page, isolate_mode))
>> +				if (!isolate_movable_page(head, isolate_mode)) {
>> +					low_pfn += (1 << compound_order(head)) - 1 - (page - head);
>> +					page = head;
>>  					goto isolate_success;
>> +				}
>>  			}
>>
>>  			goto isolate_fail;
>
>
> -- 
> Thanks,
>
> David / dhildenb


--
Best Regards,
Yan, Zi

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