Re: [PATCH v2] mm: Fix for negative counter: nr_file_hugepages

[Matthew Wilcox <willy@xxxxxxxxxxxxx>]

On Tue, Nov 07, 2023 at 03:06:16PM -0500, Johannes Weiner wrote:
> On Tue, Nov 07, 2023 at 07:35:37PM +0000, Matthew Wilcox wrote:
> > On Tue, Nov 07, 2023 at 10:18:05AM -0800, Stefan Roesch wrote:
> > > +++ b/mm/huge_memory.c
> > > @@ -2740,7 +2740,7 @@ int split_huge_page_to_list(struct page *page, struct list_head *list)
> > >  			if (folio_test_swapbacked(folio)) {
> > >  				__lruvec_stat_mod_folio(folio, NR_SHMEM_THPS,
> > >  							-nr);
> > > -			} else {
> > > +			} else if (folio_test_pmd_mappable(folio)) {
> > >  				__lruvec_stat_mod_folio(folio, NR_FILE_THPS,
> > >  							-nr);
> > >  				filemap_nr_thps_dec(mapping);
> > 
> > As I said, we also need the folio_test_pmd_mappable() for swapbacked.
> > Not because there's currently a problem, but because we don't leave
> > landmines for other people to trip over in future!
> 
> Do we need to fix filemap_unaccount_folio() as well?

Looks to me like it is already correct?

        __lruvec_stat_mod_folio(folio, NR_FILE_PAGES, -nr);
        if (folio_test_swapbacked(folio)) {
                __lruvec_stat_mod_folio(folio, NR_SHMEM, -nr);
                if (folio_test_pmd_mappable(folio))
                        __lruvec_stat_mod_folio(folio, NR_SHMEM_THPS, -nr);
        } else if (folio_test_pmd_mappable(folio)) {
                __lruvec_stat_mod_folio(folio, NR_FILE_THPS, -nr);
                filemap_nr_thps_dec(mapping);
        }