linux-kernel - Re: [PATCH 04/11] mm: add PG

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Message-ID: <2dde1a51-f4c2-4e0b-8ac6-b9859e194304@redhat.com>
Date: Fri, 20 Dec 2024 16:20:00 +0100
From: David Hildenbrand <david@...hat.com>
To: "Kirill A. Shutemov" <kirill@...temov.name>
Cc: Jens Axboe <axboe@...nel.dk>, linux-mm@...ck.org,
 linux-fsdevel@...r.kernel.org, hannes@...xchg.org, clm@...a.com,
 linux-kernel@...r.kernel.org, willy@...radead.org, bfoster@...hat.com,
 Vlastimil Babka <vbabka@...e.cz>
Subject: Re: [PATCH 04/11] mm: add PG_dropbehind folio flag

On 20.12.24 16:12, Kirill A. Shutemov wrote:
> On Fri, Dec 20, 2024 at 04:03:44PM +0100, David Hildenbrand wrote:
>> On 20.12.24 12:08, Kirill A. Shutemov wrote:
>>> On Fri, Dec 13, 2024 at 08:55:18AM -0700, Jens Axboe wrote:
>>>> Add a folio flag that file IO can use to indicate that the cached IO
>>>> being done should be dropped from the page cache upon completion.
>>>>
>>>> Signed-off-by: Jens Axboe <axboe@...nel.dk>
>>>
>>> Reviewed-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
>>>
>>> + David, Vlastimil.
>>>
>>> I think we should consider converting existing folio_set_reclaim() /
>>> SetPageReclaim() users to the new flag. From a quick scan, all of them
>>> would benefit from dropping the page after writeback is complete instead
>>> of leaving the folio on the LRU.
>>
>> I wonder of there are some use cases where we write a lot of data to then
>> only consume it read-only from that point on (databases? fancy AI stuff? no
>> idea :) ).
> 
> Do we use PG_reclaim for such cases?

Good point, I looked at the pageout() case, but there we really want to 
pageout that thing and not just write it back, so makes sense to me.

-- 
Cheers,

David / dhildenb