On Thu, Oct 17, 2024 at 02:58:03PM -0700, chrisl@xxxxxxxxxx wrote:
> From: Yu Zhao <yuzhao@xxxxxxxxxx>
>
> [ Upstream commit 95599ef684d01136a8b77c16a7c853496786e173 ]
>
> The current assumption is that a large folio can only be split into
> order-0 folios. That is not the case for hugeTLB demotion, nor for THP
> split: see commit c010d47f107f ("mm: thp: split huge page to any lower
> order pages").
>
> When a large folio is split into ones of a lower non-zero order, only the
> new head pages should be tagged. Tagging tail pages can cause imbalanced
> "calls" counters, since only head pages are untagged by pgalloc_tag_sub()
> and the "calls" counts on tail pages are leaked, e.g.,
>
> # echo 2048kB >/sys/kernel/mm/hugepages/hugepages-1048576kB/demote_size
> # echo 700 >/sys/kernel/mm/hugepages/hugepages-1048576kB/nr_hugepages
> # time echo 700 >/sys/kernel/mm/hugepages/hugepages-1048576kB/demote
> # echo 0 >/sys/kernel/mm/hugepages/hugepages-2048kB/nr_hugepages
> # grep alloc_gigantic_folio /proc/allocinfo
>
> Before this patch:
> 0 549427200 mm/hugetlb.c:1549 func:alloc_gigantic_folio
>
> real 0m2.057s
> user 0m0.000s
> sys 0m2.051s
>
> After this patch:
> 0 0 mm/hugetlb.c:1549 func:alloc_gigantic_folio
>
> real 0m1.711s
> user 0m0.000s
> sys 0m1.704s
>
> Not tagging tail pages also improves the splitting time, e.g., by about
> 15% when demoting 1GB hugeTLB folios to 2MB ones, as shown above.
>
> Link: https://lkml.kernel.org/r/20240906042108.1150526-2-yuzhao@xxxxxxxxxx
> Fixes: be25d1d4e822 ("mm: create new codetag references during page splitting")
> Signed-off-by: Yu Zhao <yuzhao@xxxxxxxxxx>
> Acked-by: Suren Baghdasaryan <surenb@xxxxxxxxxx>
> Cc: Kent Overstreet <kent.overstreet@xxxxxxxxx>
> Cc: Muchun Song <muchun.song@xxxxxxxxx>
> Cc: <stable@xxxxxxxxxxxxxxx>
> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
You did not sign off on this backport, so even if I wanted to take it, I
couldn't :(
Please fix this, and patch 3/3 up, and just send those.
sorry,
greg k-h
