Re: [PATCH] mm: page_alloc: use the correct THP order for THP PCP

[Baolin Wang]

On 2024/4/5 12:53, Barry Song wrote:
> On Thu, Apr 4, 2024 at 2:47 AM Baolin Wang
> <baolin.wang@xxxxxxxxxxxxxxxxx> wrote:
> > Commit 44042b449872 ("mm/page_alloc: allow high-order pages to be stored
> > on the per-cpu lists") extends the PCP allocator to store THP pages, and
> > it determines whether to cache THP pags in PCP by comparing with pageblock_order.
> > But the pageblock_order is not always equal to THP order, it might also
> > be MAX_PAGE_ORDER, which could prevent PCP from caching THP pages.
> >
> > Therefore, using HPAGE_PMD_ORDER instead to determine the need for caching
> > THP for PCP can fix this issue
> >
> > Fixes: 44042b449872 ("mm/page_alloc: allow high-order pages to be stored on the per-cpu lists")
> > Signed-off-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
>
> LGTM,
> Reviewed-by: Barry Song <baohua@xxxxxxxxxx>
>
> In the context of using mTHP, perhaps there arises a need for PCP
> allocation for frequently
> requested mTHP orders. These orders typically exceed PAGE_ALLOC_COSTLY_ORDER
> but are smaller than HPAGE_PMD_ORDER.

Yes, I have also considered this, but haven't found some time to do more 
investigation and run some benchmarks.:) May be we can create a new 
thread to talk about this first.