Re: [PATCH] writeback: Account the number of pages written back

[Dave Chinner]

On Mon, Jul 03, 2023 at 03:13:15AM +0100, Matthew Wilcox wrote:
> On Sun, Jul 02, 2023 at 01:06:15PM -0700, Andrew Morton wrote:
> > On Wed, 28 Jun 2023 19:55:48 +0100 "Matthew Wilcox (Oracle)" <willy@xxxxxxxxxxxxx> wrote:
> > 
> > > nr_to_write is a count of pages, so we need to decrease it by the number
> > > of pages in the folio we just wrote, not by 1.  Most callers specify
> > > either LONG_MAX or 1, so are unaffected, but writeback_sb_inodes()
> > > might end up writing 512x as many pages as it asked for.
> > 
> > 512 is a big number,  Should we backport this?
> 
> I'm really not sure.  Maybe?  I'm hoping one of the bots comes up with a
> meaningful performance change as a result of this patch and we find out.

XFS is the only filesystem this would affect, right? AFAIA, nothing
else enables large folios and uses writeback through
write_cache_pages() at this point...

In which case, I'd be surprised if much difference, if any, gets
noticed by anyone.

-Dave.
-- 
Dave Chinner
david@xxxxxxxxxxxxx