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Message-ID: <a39c8602-3c9c-48fd-9bdb-2089ccccd6bc@redhat.com>
Date: Wed, 12 Jun 2024 09:32:01 +0200
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Subject: Re: [PATCH] mm/gup: don't check page lru flag before draining it
To: yangge1116 <yangge1116@126.com>, Matthew Wilcox <willy@infradead.org>
Cc: Baolin Wang <baolin.wang@linux.alibaba.com>, akpm@linux-foundation.org,
 linux-mm@kvack.org, linux-kernel@vger.kernel.org, liuzixing@hygon.cn
References: <0d7a4405-9a2e-4bd1-ba89-a31486155233@redhat.com>
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 <48150a28-ed48-49ff-9432-9cd30cda4da4@linux.alibaba.com>
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 <d6deb928-3466-45ea-939b-cb5aca9bc7b4@linux.alibaba.com>
 <3a368e38-a4cb-413e-a6d9-41c6b3dbd5ae@redhat.com>
 <48fb0e58-16d1-7956-cf35-74741826617a@126.com>
 <ZmR1dVUB5mE2If9t@casper.infradead.org>
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From: David Hildenbrand <david@redhat.com>
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On 11.06.24 13:20, yangge1116 wrote:
> 
> 
> 在 2024/6/9 上午12:03, David Hildenbrand 写道:
>> On 08.06.24 17:15, Matthew Wilcox wrote:
>>> On Sat, Jun 08, 2024 at 12:38:49PM +0800, yangge1116 wrote:
>>>> Can we add a PG_lru_batch flag to determine whether a page is in lru
>>>> batch?
>>>> If we can, seems this problem will be easier.
>>>
>>> Page flags are in short supply.  You'd need a really good justification.
>>>
>>
>> A flag would not be able to handle the "part of multiple LRU batches"
>> that should currently possible (when to clear the flag?). Well, if we
>> have to keep supporting that. If we only to be part in a single LRU
>> batch, a new flag could work and we could still allow isolating a folio
>> from LRU while in some LRU batch.
> 
> Yes, before adding a folio to LRU batch, check whether the folio has
> been added. Add the folio to LRU batch only if the folio has not been
> added.
> 
>>
>> If we could handle it using the existing flags, that would of course be
>> better (wondering if we could store more information in the existing
>> flags by using a different encoding for the different states).
> 
> If a folio contains more than one page, the folio will not be added to
> LRU batch. Can we use folio_test_large(folio) to filter?
> 
> if (!folio_test_large(folio) && drain_allow) {
> 	lru_add_drain_all();
> 	drain_allow = false;
> }

I think we should do better than this, and not do arbitrary 
lru_add_drain_all() calls.

-- 
Cheers,

David / dhildenb