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

[yangge1116]

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.