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SubjectRe: [PATCH] writeback: Account the number of pages written back
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@infradead.org> 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@fromorbit.com

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