linux-kernel - Re: [PATCH 03/13] mm: add PG

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Message-ID: <75bf5237-efc4-4fb7-9e24-061354bff9ac@kernel.dk>
Date: Fri, 8 Nov 2024 12:39:48 -0700
From: Jens Axboe <axboe@...nel.dk>
To: "Kirill A. Shutemov" <kirill@...temov.name>
Cc: linux-mm@...ck.org, linux-fsdevel@...r.kernel.org, hannes@...xchg.org,
 clm@...a.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 03/13] mm: add PG_uncached page flag

On 11/8/24 12:25 PM, Kirill A. Shutemov wrote:
> On Fri, Nov 08, 2024 at 10:43:26AM -0700, Jens Axboe wrote:
>> Add a page flag that file IO can use to indicate that the IO being done
>> is uncached, as in it should not persist in the page cache after the IO
>> has been completed.
> 
> Flag bits are precious resource. It would be nice to re-use an existing
> bit if possible.

I knoew, like I mentioned in the reply to willy, I knew this one would
be an interesting discussion in and of itself.

> PG_reclaim description looks suspiciously close to what you want.
> I wounder if it would be valid to re-define PG_reclaim behaviour to drop
> the page after writeback instead of moving to the tail of inactive list.

You're the mm expert - I added the flag since then it has a clearly
defined meaning, and I would not need to worry about any kind of odd
overlap in paths I didn't know about. Would definitely entertain reusing
something else, but I'll leave that in the hands of the people that know
this code and the various intricacies and assumptions a lot better than
I do.

-- 
Jens Axboe