On Thu, Jul 13, 2023 at 9:10 PM Yin, Fengwei <fengwei.yin@xxxxxxxxx> wrote: > > > > On 7/14/2023 10:08 AM, Yu Zhao wrote: > > On Thu, Jul 13, 2023 at 9:06 AM Yin Fengwei <fengwei.yin@xxxxxxxxx> wrote: > >> > >> Current madvise_cold_or_pageout_pte_range() has two problems for > >> large folio support: > >> - Using folio_mapcount() with large folio prevent large folio from > >> picking up. > >> - If large folio is in the range requested, shouldn't split it > >> in madvise_cold_or_pageout_pte_range(). > >> > >> Fix them by: > >> - Use folio_estimated_sharers() with large folio > >> - If large folio is in the range requested, don't split it. Leave > >> to page reclaim phase. > >> > >> For large folio cross boundaries of requested range, skip it if it's > >> page cache. Try to split it if it's anonymous folio. If splitting > >> fails, skip it. > > > > For now, we may not want to change the existing semantic (heuristic). > > IOW, we may want to stick to the "only owner" condition: > > > > - if (folio_mapcount(folio) != 1) > > + if (folio_entire_mapcount(folio) || > > + (any_page_within_range_has_mapcount > 1)) > > > > +Minchan Kim > The folio_estimated_sharers() was discussed here: > https://lore.kernel.org/linux-mm/20230118232219.27038-6-vishal.moola@xxxxxxxxx/ > https://lore.kernel.org/linux-mm/20230124012210.13963-2-vishal.moola@xxxxxxxxx/ > > Yes. It's accurate to check each page of large folio. But it may be over killed in > some cases (And I think madvise is one of the cases not necessary to be accurate. > So folio_estimated_sharers() is enough. Correct me if I am wrong). I see. Then it's possible this is also what the original commit wants to do -- Minchan, could you clarify? Regardless, I think we can have the following fix, potentially cc'ing stable: - if (folio_mapcount(folio) != 1) + if (folio_estimated_sharers(folio) != 1) Sounds good? > > Also there is an existing bug here: the later commit 07e8c82b5eff8 > > ("madvise: convert madvise_cold_or_pageout_pte_range() to use folios") > > is incorrect for sure; the original commit 9c276cc65a58f ("mm: > > introduce MADV_COLD") seems incorrect too. > > > > +Vishal Moola (Oracle) > > > > The "any_page_within_range_has_mapcount" test above seems to be the > > only correct to meet condition claimed by the comments, before or > > after the folio conversion, assuming here a THP page means the > > compound page without PMD mappings (PMD-split). Otherwise the test is > > always false (if it's also PMD mapped somewhere else). > > > > /* > > * Creating a THP page is expensive so split it only if we > > * are sure it's worth. Split it if we are only owner. > > */
