Re: [PATCH v4 3/4] mm/huge_memory: add a per-order counter for underused splits

[Baolin Wang <baolin.wang@linux.alibaba.com>]

On 11/4/26 5:20 AM, Joanne Koong wrote:
> thp_underused_split_page counts every folio that the deferred split
> shrinker splits for being underused. Today that is only ever a
> PMD-sized folio, but a later patch queues anonymous mTHP folios for
> underused splitting too, at which point this counter would start
> counting mTHP splits as well.
> 
> thp_underused_split_page could then end up larger than thp_split_page,
> and there would be no per-order count of underused splits. That doesn't
> match how the other THP split stats work. In /proc/vmstat,
> thp_split_page and thp_deferred_split_page only count PMD-sized folios.
> Splits of every size, PMD included, are counted per order in the split
> and split_deferred stats under hugepages-<size>/stats/.
> 
> Do the same for underused splits. Only count PMD-sized folios in
> thp_underused_split_page, and add a per-order split_underused stat that
> counts underused splits of every size. The folio's order has to be read
> before splitting it, since the folio is no longer large once the split
> succeeds.
> 
> There is no functional change to thp_underused_split_page yet, as only
> PMD-sized folios are split for being underused today.
> 
> Suggested-by: Kiryl Shutsemau <kas@kernel.org>
> Signed-off-by: Joanne Koong <joannelkoong@gmail.com>
> ---

LGTM.
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>