Re: [PATCH 3/4] mm/readahead: add a_ops->ra_folio_order to get a desired folio order

Jaegeuk Kim
2025-12-02T01:33:02Z

On 12/01, Matthew Wilcox wrote:
> 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.

I got that, and posted v2.

Thanks,