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

[Jaegeuk Kim]

On 05/31, Barry Song via Linux-f2fs-devel wrote:
> 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,

Hi Barry,

> 
> 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.

Yeah, I was about to reach out to you. Let's do some discussion
offline.

Thanks,

> 
> Best regards,
> Barry
> 
> 
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