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
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.
*/
> The main reason to call folio_referenced() is to clear the yong of
> conresponding PTEs. So in page reclaim phase, there is good chance
> the folio can be reclaimed.
>
> Signed-off-by: Yin Fengwei <fengwei.yin@xxxxxxxxx>
> ---
> This patch is based on mlock large folio support rfc2 as it depends
> on the folio_in_range() added by that patchset
>
> Also folio_op_size() can be unitfied with get_folio_mlock_step().
>
> Testing done:
> - kselftest: No new regression introduced.
>
> mm/madvise.c | 133 ++++++++++++++++++++++++++++++++-------------------
> 1 file changed, 84 insertions(+), 49 deletions(-)
Also the refactor looks fine to me but it'd be better if it's a separate patch.
