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Date: Wed, 12 Feb 2025 00:39:04 +0000
From: Jaegeuk Kim <jaegeuk@kernel.org>
To: Matthew Wilcox <willy@infradead.org>
Cc: linux-kernel@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net,
	linux-mm@kvack.org, linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH 0/2 v6] add ioctl/sysfs to donate file-backed pages
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In-Reply-To: <Z6pNBxgMKHTiHAnv@google.com>

On 02/10, Jaegeuk Kim wrote:
> On 02/10, Matthew Wilcox wrote:
> > On Mon, Feb 10, 2025 at 05:00:47PM +0000, Jaegeuk Kim wrote:
> > > On 02/04, Jaegeuk Kim wrote:
> > > > On 01/17, Jaegeuk Kim wrote:
> > > > > On 01/17, Matthew Wilcox wrote:
> > > > > > On Fri, Jan 17, 2025 at 06:48:55PM +0000, Jaegeuk Kim wrote:
> > > > > > > > I don't understand how this is different from MADV_COLD.  Please
> > > > > > > > explain.
> > > > > > > 
> > > > > > > MADV_COLD is a vma range, while this is a file range. So, it's more close to
> > > > > > > fadvise(POSIX_FADV_DONTNEED) which tries to reclaim the file-backed pages
> > > > > > > at the time when it's called. The idea is to keep the hints only, and try to
> > > > > > > reclaim all later when admin expects system memory pressure soon.
> > > > > > 
> > > > > > So you're saying you want POSIX_FADV_COLD?
> > > > > 
> > > > > Yeah, the intention looks similar like marking it cold and paging out later.
> > > > 
> > > > Kindly ping, for the feedback on the direction. If there's demand for something
> > > > generalized api, I'm happy to explore.
> > > 
> > > If there's no objection, let me push the change in f2fs and keep an eye on
> > > who more will need this in general.
> > 
> > I don't know why you're asking for direction.  I gave my direction: use
> > fadvise().
> 
> Funny, that single question didn't mean like this at all. Will take a look
> how the patch looks like.

Ok, it seems we can get this hint via POSIX_FADV_NOREUSE. I'll take that
instead of adding a new API. Thanks.

> 
> > 
> > Putting this directly in f2fs is a horrible idea.  NAK.