Re: [PATCH] mm/page_alloc: skip THP-sized PCP list when allocating non-CMA THP-sized page

[Baolin Wang]

On 2024/6/4 20:36, yangge1116 wrote:
> 在 2024/6/4 下午8:01, Baolin Wang 写道:
> > Cc Johannes, Zi and Vlastimil.
> >
> > On 2024/6/4 17:14, yangge1116@xxxxxxx wrote:
> > > From: yangge <yangge1116@xxxxxxx>
> > >
> > > Since commit 5d0a661d808f ("mm/page_alloc: use only one PCP list for
> > > THP-sized allocations") no longer differentiates the migration type
> > > of pages in THP-sized PCP list, it's possible to get a CMA page from
> > > the list, in some cases, it's not acceptable, for example, allocating
> > > a non-CMA page with PF_MEMALLOC_PIN flag returns a CMA page.
> > >
> > > The patch forbids allocating non-CMA THP-sized page from THP-sized
> > > PCP list to avoid the issue above.
> > >
> > > Fixes: 5d0a661d808f ("mm/page_alloc: use only one PCP list for 
> > > THP-sized allocations")
> > > Signed-off-by: yangge <yangge1116@xxxxxxx>
> > > ---
> > >   mm/page_alloc.c | 10 ++++++++++
> > >   1 file changed, 10 insertions(+)
> > >
> > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> > > index 2e22ce5..0bdf471 100644
> > > --- a/mm/page_alloc.c
> > > +++ b/mm/page_alloc.c
> > > @@ -2987,10 +2987,20 @@ struct page *rmqueue(struct zone 
> > > *preferred_zone,
> > >       WARN_ON_ONCE((gfp_flags & __GFP_NOFAIL) && (order > 1));
> > >       if (likely(pcp_allowed_order(order))) {
> > > +#ifdef CONFIG_TRANSPARENT_HUGEPAGE
> > > +        if (!IS_ENABLED(CONFIG_CMA) || alloc_flags & ALLOC_CMA ||
> > > +                        order != HPAGE_PMD_ORDER) {
> >
> > Seems you will also miss the non-CMA THP from the PCP, so I wonder if 
> > we can add a migratetype comparison in __rmqueue_pcplist(), and if 
> > it's not suitable, then fallback to buddy?
>
> Yes, we may miss some non-CMA THPs in the PCP. But, if add a migratetype 
> comparison in __rmqueue_pcplist(), we may need to compare many times 
> because of pcp batch.

I mean we can only compare once, focusing on CMA pages.

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 3734fe7e67c0..960a3b5744d8 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -2973,6 +2973,11 @@ struct page *__rmqueue_pcplist(struct zone *zone, 
unsigned int order,
                }

                page = list_first_entry(list, struct page, pcp_list);
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+               if (order == HPAGE_PMD_ORDER && 
!is_migrate_movable(migratetype) &&
+                   is_migrate_cma(get_pageblock_migratetype(page)))
+                       return NULL;
+#endif
                list_del(&page->pcp_list);
                pcp->count -= 1 << order;
        } while (check_new_pages(page, order));