linux-kernel - Re: [PATCH 3/4] mm/readahead: add a_ops->ra_folio

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <aS4K3jGkJErj94R_@casper.infradead.org>
Date: Mon, 1 Dec 2025 21:38:38 +0000
From: Matthew Wilcox <willy@...radead.org>
To: Jaegeuk Kim <jaegeuk@...nel.org>
Cc: linux-kernel@...r.kernel.org, linux-f2fs-devel@...ts.sourceforge.net,
	linux-mm@...ck.org
Subject: Re: [PATCH 3/4] mm/readahead: add a_ops->ra_folio_order to get a
 desired folio order

On Mon, Dec 01, 2025 at 09:24:41PM +0000, Jaegeuk Kim wrote:
> On 12/01, Matthew Wilcox wrote:
> > On Mon, Dec 01, 2025 at 09:01:26PM +0000, Jaegeuk Kim wrote:
> > > This patch introduces a new address operation, a_ops->ra_folio_order(), which
> > > proposes a new folio order based on the adjusted order for page_cache_sync_ra.
> > > 
> > > Hence, each filesystem can set the desired minimum order of folio allocation
> > > when requesting fadvise(POSIX_FADV_WILLNEED).
> > 
> > Again, you've said what but not why.  Does the mm code not ramp up the
> > folio order sufficiently quickly?  What are you trying to accomplish?
> 
> That's why I posted a series of the patches to provide more details. Could you
> please check the last patch in the series to show fadvise() does not increase
> the folio order?
> 
> https://lore.kernel.org/linux-f2fs-devel/20251201210152.909339-5-jaegeuk@kernel.org/T/#u

So what you're trying to say is that readahead() currently only uses
order-0 pages and you want it to use larger order pages?  I agree with
that!  But I don't think this is the way to do it.  We should just use
larger order allocations, always.  None of this "call the filesystem,
check a sysfs parameter".  Just use the largest order page that fits.