Re: [f2fs-dev] [PATCH v2] f2fs: another way to set large folio by remembering inode number

[Barry Song]

On Sun, May 31, 2026 at 8:12 AM Jaegeuk Kim <jaegeuk@xxxxxxxxxx> wrote:
>
> On 05/28, Christoph Hellwig wrote:
> > On Wed, May 27, 2026 at 03:59:35PM +0000, Jaegeuk Kim wrote:
> > > F2FS merges bios before submit_bio, regardless of small or large folios,
> > > since the block addresses are consecutive. So, I think IO subsystem was
> > > working in full speed.
> >
> > As does every other remotely modern file system.  But that merging is
> > surprisingly expensive, which is why using folios gets really major
> > performance improvements.
> >
> > For one doing these checks to merge touch quite a few cache lines.
> > Second, devices are often a lot more efficient if they see fewer SGL
> > entries.  I.e. having a 1MB bio a single SGL tends to work better than
> > having 256 of them.
> > The same is true in the kernel code itself, both in the submission path
> > (dma mapping and co), and even more so in the page cache handling
> > both before submitting and in the completion path.
> >
> > See Bart's patch about how long the walk of the bio_vecs in the f2fs
> > completion path can take.  We had similar issues in XFS even in the
> > workqueue completion path due to lack of rescheduling, and these simply
> > go away when you do the folio manipulation in larger chunks (LAZY_PREEMPT
> > would avoid the need to explicit rescheduling these days, but that just
> > papers over the symptoms in this case).
> >
>
> I see. That's also super helpful. Let me kick off the large folio support asap.
> Thanks.

Hi Jaegeuk,

Nanzhe has put significant effort into this work at Xiaomi over
the past several months. Large folios can now be supported on
non-immutable files.

He has conducted extensive testing on the Pixel 6 and fixed a
number of hangs discovered during development. He is still
benchmarking performance, but the implementation appears to be
reasonably stable at this point. We can run Android Monkey for
many hours without observing any hangs.

If you would like to see an RFC, I can ask Nanzhe to send one
as soon as possible after some cleanup and polishing.

Best regards,
Barry