linux-kernel - Re: [PATCH 0/2 v6] add ioctl/sysfs to donate file-backed pages

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Message-ID: <Z4qmF2n2pzuHqad_@google.com>
Date: Fri, 17 Jan 2025 18:48:55 +0000
From: Jaegeuk Kim <jaegeuk@...nel.org>
To: Matthew Wilcox <willy@...radead.org>
Cc: linux-kernel@...r.kernel.org, linux-f2fs-devel@...ts.sourceforge.net,
	linux-mm@...ck.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH 0/2 v6] add ioctl/sysfs to donate file-backed pages

On 01/17, Matthew Wilcox wrote:
> On Fri, Jan 17, 2025 at 04:41:16PM +0000, Jaegeuk Kim wrote:
> > If users clearly know which file-backed pages to reclaim in system view, they
> > can use this ioctl() to register in advance and reclaim all at once later.
> > 
> > To MM and others,
> > 
> > I'd like to propose this API in F2FS only, since
> > 1) the use-case is quite limited in Android at the moment. Once it's generall
> > accepted with more use-cases, happy to propose a generic API such as fadvise.
> > Please chime in, if there's any needs.
> > 
> > 2) it's file-backed pages which requires to maintain the list of inode objects.
> > I'm not sure this fits in MM tho, also happy to listen to any feedback.
> 
> You didn't cc the patches to linux-mm, so that's a bad start.

Because #1.

> 
> 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.