Re: Multi-page folio issues in 5.19-rc4 (was [PATCH v3 25/25] xfs: Support large folios)

["Darrick J. Wong" <djwong@kernel.org>]

On Wed, Jun 29, 2022 at 08:17:57AM +1000, Dave Chinner wrote:
> On Tue, Jun 28, 2022 at 02:18:24PM +0100, Matthew Wilcox wrote:
> > On Tue, Jun 28, 2022 at 12:31:55PM +0100, Matthew Wilcox wrote:
> > > On Tue, Jun 28, 2022 at 12:27:40PM +0100, Matthew Wilcox wrote:
> > > > On Tue, Jun 28, 2022 at 05:31:20PM +1000, Dave Chinner wrote:
> > > > > So using this technique, I've discovered that there's a dirty page
> > > > > accounting leak that eventually results in fsx hanging in
> > > > > balance_dirty_pages().
> > > > 
> > > > Alas, I think this is only an accounting error, and not related to
> > > > the problem(s) that Darrick & Zorro are seeing.  I think what you're
> > > > seeing is dirty pages being dropped at truncation without the
> > > > appropriate accounting.  ie this should be the fix:
> > > 
> > > Argh, try one that actually compiles.
> > 
> > ... that one's going to underflow the accounting.  Maybe I shouldn't
> > be writing code at 6am?
> > 
> > diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> > index f7248002dad9..4eec6ee83e44 100644
> > --- a/mm/huge_memory.c
> > +++ b/mm/huge_memory.c
> > @@ -18,6 +18,7 @@
> >  #include <linux/shrinker.h>
> >  #include <linux/mm_inline.h>
> >  #include <linux/swapops.h>
> > +#include <linux/backing-dev.h>
> >  #include <linux/dax.h>
> >  #include <linux/khugepaged.h>
> >  #include <linux/freezer.h>
> > @@ -2439,11 +2440,15 @@ static void __split_huge_page(struct page *page, struct list_head *list,
> >  		__split_huge_page_tail(head, i, lruvec, list);
> >  		/* Some pages can be beyond EOF: drop them from page cache */
> >  		if (head[i].index >= end) {
> > -			ClearPageDirty(head + i);
> > -			__delete_from_page_cache(head + i, NULL);
> > +			struct folio *tail = page_folio(head + i);
> > +
> >  			if (shmem_mapping(head->mapping))
> >  				shmem_uncharge(head->mapping->host, 1);
> > -			put_page(head + i);
> > +			else if (folio_test_clear_dirty(tail))
> > +				folio_account_cleaned(tail,
> > +					inode_to_wb(folio->mapping->host));
> > +			__filemap_remove_folio(tail, NULL);
> > +			folio_put(tail);
> >  		} else if (!PageAnon(page)) {
> >  			__xa_store(&head->mapping->i_pages, head[i].index,
> >  					head + i, 0);
> > 
> 
> Yup, that fixes the leak.
> 
> Tested-by: Dave Chinner <dchinner@redhat.com>

Four hours of generic/522 running is long enough to conclude that this
is likely the fix for my problem and migrate long soak testing to my
main g/522 rig and:

Tested-by: Darrick J. Wong <djwong@kernel.org>

--D

> Cheers,
> 
> Dave.
> -- 
> Dave Chinner
> david@fromorbit.com