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: <99D30A79-7B57-4FCB-8C7A-7F93B66490E6@nvidia.com>
Date:   Thu, 13 Jan 2022 11:23:37 -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 13 Jan 2022, at 9:57, Zi Yan wrote:

> 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.

I will drop this one too. Like you mentioned in [1], there are no
non-lru migratable compound pages. This is only used by my local
test code.

[1] https://lore.kernel.org/linux-mm/970ca2a4-416d-7e8f-37c7-510c5b050f4b@redhat.com/


>
>>> 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


--
Best Regards,
Yan, Zi

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