linux-kernel - Re: [RFC PATCH] block, fs: use FOLL_LONGTERM as gup

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Message-ID: <CAJrd-UuLvOPLC2Xr=yOzZYvOw9k8qwbNa0r9oNjne31x8Pmnhw@mail.gmail.com>
Date: Fri, 7 Mar 2025 08:28:41 +0900
From: Jaewon Kim <jaewon31.kim@...il.com>
To: Christoph Hellwig <hch@...radead.org>
Cc: Sooyong Suk <s.suk@...sung.com>, viro@...iv.linux.org.uk, 
	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org, linux-mm@...ck.org, 
	spssyr@...il.com, "axboe@...nel.dk" <axboe@...nel.dk>, linux-block@...r.kernel.org, 
	dhavale@...gle.com, surenb@...gle.com
Subject: Re: [RFC PATCH] block, fs: use FOLL_LONGTERM as gup_flags for direct IO

On Fri, Mar 7, 2025 at 12:26 AM Christoph Hellwig <hch@...radead.org> wrote:
>
> On Thu, Mar 06, 2025 at 04:40:56PM +0900, Sooyong Suk wrote:
> > There are GUP references to pages that are serving as direct IO buffers.
> > Those pages can be allocated from CMA pageblocks despite they can be
> > pinned until the DIO is completed.
>
> direct I/O is eactly the case that is not FOLL_LONGTERM and one of
> the reasons to even have the flag.  So big fat no to this.
>

Hello, thank you for your comment.
We, Sooyong and I, wanted to get some opinions about this
FOLL_LONGTERM for direct I/O as CMA memory got pinned pages which had
been pinned from direct io.

> You also completely failed to address the relevant mailinglist and
> maintainers.

I added block maintainer Jens Axboe and the block layer maillinst
here, and added Suren and Sandeep, too.