linux-ext4 - Re: [PATCH 03/16] mm: add PG

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Message-ID: <lponnb7dxjx3htksbggjoasvby6sa2a4ayrkcykdnxvypwy4pp@ci2fnmcyrke7>
Date: Tue, 12 Nov 2024 11:12:15 +0200
From: "Kirill A. Shutemov" <kirill@...temov.name>
To: Jens Axboe <axboe@...nel.dk>
Cc: linux-mm@...ck.org, linux-fsdevel@...r.kernel.org, hannes@...xchg.org, 
	clm@...a.com, linux-kernel@...r.kernel.org, willy@...radead.org, 
	linux-btrfs@...r.kernel.org, linux-ext4@...r.kernel.org, linux-xfs@...r.kernel.org
Subject: Re: [PATCH 03/16] mm: add PG_uncached page flag

On Mon, Nov 11, 2024 at 04:37:30PM -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.

I have not found a way to avoid using a new bit. I am unsure if we have
enough bits on 32-bit systems with all possible features enabled.

In the worst-case scenario, we may need to make the feature 64-bit only.
I believe it should be acceptable as long as userspace is prepared for the
possibility that RWF_UNCACHED may fail. It is not going to be supported by
all filesystems anyway.

-- 
  Kiryl Shutsemau / Kirill A. Shutemov