Baolin Wang's patch[1] has avoided confusion with PMD mapped THP related statistics. So, these three counters (THP_SPLIT_PAGE, THP_SPLIT_PAGE_FAILED, and THP_DEFERRED_SPLIT_PAGE) no longer include mTHP. [1] https://lore.kernel.org/linux-mm/a5341defeef27c9ac7b85c97f030f93e4368bbc1.1711694852.git.baolin.wang@xxxxxxxxxxxxxxxxx/ On Tue, Apr 2, 2024 at 9:10 PM Ryan Roberts <ryan.roberts@xxxxxxx> wrote: > > On 28/03/2024 08:18, Barry Song wrote: > > On Thu, Mar 28, 2024 at 3:45 AM Ryan Roberts <ryan.roberts@xxxxxxx> wrote: > >> > >> Now that swap supports storing all mTHP sizes, avoid splitting large > >> folios before swap-out. This benefits performance of the swap-out path > >> by eliding split_folio_to_list(), which is expensive, and also sets us > >> up for swapping in large folios in a future series. > >> > >> If the folio is partially mapped, we continue to split it since we want > >> to avoid the extra IO overhead and storage of writing out pages > >> uneccessarily. > >> > >> Reviewed-by: David Hildenbrand <david@xxxxxxxxxx> > >> Reviewed-by: Barry Song <v-songbaohua@xxxxxxxx> > >> Signed-off-by: Ryan Roberts <ryan.roberts@xxxxxxx> > >> --- > >> mm/vmscan.c | 9 +++++---- > >> 1 file changed, 5 insertions(+), 4 deletions(-) > >> > >> diff --git a/mm/vmscan.c b/mm/vmscan.c > >> index 00adaf1cb2c3..293120fe54f3 100644 > >> --- a/mm/vmscan.c > >> +++ b/mm/vmscan.c > >> @@ -1223,11 +1223,12 @@ static unsigned int shrink_folio_list(struct list_head *folio_list, > >> if (!can_split_folio(folio, NULL)) > >> goto activate_locked; > >> /* > >> - * Split folios without a PMD map right > >> - * away. Chances are some or all of the > >> - * tail pages can be freed without IO. > >> + * Split partially mapped folios right > >> + * away. We can free the unmapped pages > >> + * without IO. > >> */ > >> - if (!folio_entire_mapcount(folio) && > >> + if (data_race(!list_empty( > >> + &folio->_deferred_list)) && > >> split_folio_to_list(folio, > >> folio_list)) > >> goto activate_locked; > > > > Hi Ryan, > > > > Sorry for bringing up another minor issue at this late stage. > > No problem - I'd rather take a bit longer and get it right, rather than rush it > and get it wrong! > > > > > During the debugging of thp counter patch v2, I noticed the discrepancy between > > THP_SWPOUT_FALLBACK and THP_SWPOUT. > > > > Should we make adjustments to the counter? > > Yes, agreed; we want to be consistent here with all the other existing THP > counters; they only refer to PMD-sized THP. I'll make the change for the next > version. > > I guess we will eventually want equivalent counters for per-size mTHP using the > framework you are adding. > > > > > diff --git a/mm/vmscan.c b/mm/vmscan.c > > index 293120fe54f3..d7856603f689 100644 > > --- a/mm/vmscan.c > > +++ b/mm/vmscan.c > > @@ -1241,8 +1241,10 @@ static unsigned int shrink_folio_list(struct > > list_head *folio_list, > > folio_list)) > > goto activate_locked; > > #ifdef CONFIG_TRANSPARENT_HUGEPAGE > > - > > count_memcg_folio_events(folio, THP_SWPOUT_FALLBACK, 1); > > - count_vm_event(THP_SWPOUT_FALLBACK); > > + if (folio_test_pmd_mappable(folio)) { > > + > > count_memcg_folio_events(folio, THP_SWPOUT_FALLBACK, 1); > > + > > count_vm_event(THP_SWPOUT_FALLBACK); > > + } > > #endif > > if (!add_to_swap(folio)) > > goto activate_locked_split; > > > > > > Because THP_SWPOUT is only for pmd: > > > > static inline void count_swpout_vm_event(struct folio *folio) > > { > > #ifdef CONFIG_TRANSPARENT_HUGEPAGE > > if (unlikely(folio_test_pmd_mappable(folio))) { > > count_memcg_folio_events(folio, THP_SWPOUT, 1); > > count_vm_event(THP_SWPOUT); > > } > > #endif > > count_vm_events(PSWPOUT, folio_nr_pages(folio)); > > } > > > > I can provide per-order counters for this in my THP counter patch. > > > >> -- > >> 2.25.1 > >> > > > > Thanks > > Barry >
