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

On 05/26, Christoph Hellwig wrote:
> On Tue, May 26, 2026 at 09:14:52AM -0700, Bart Van Assche wrote:
> > On 5/26/26 6:42 AM, Theodore Tso wrote:
> > > It seems... surprising that the additional I/O operations are actually
> > > throttloing UFS device bandwidth by 2x (4GB/s vs 2GB/s).  Have you dug
> > > into why this is happening, and whether there is anything that can be
> > > optimized below the file system?
> > The layers below the filesystem (block, SCSI, UFS) is what I'm
> > responsible for in the Pixel team and I can assure you that these are
> > highly optimized.
> > 
> > Since the transfer size used in Jaegeuk's tests is much larger than 4
> > KiB, how many CPU cycles are used per IO by the layers below the
> > filesystem is not limiting the transfer bandwidth.
> 
> I'm honestly not sure what discussion we have here.  Larger I/O is
> pretty much always more efficient.  If you submit smaller I/O you
> need more merging to build it back up larger, and more I/Os.

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.

> 
> Which is exaxtly why we need large folio support everywhere, as it
> makes a huge difference in I/O performance.
> 
> 
> 
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