linux-kernel - Re: [PATCH v1 1/6] mm/page_alloc: tweak comments in has_unmovable

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Message-ID: <20200729104753.GF14854@MiWiFi-R3L-srv>
Date:   Wed, 29 Jul 2020 18:47:53 +0800
From:   Baoquan He <bhe@...hat.com>
To:     David Hildenbrand <david@...hat.com>
Cc:     linux-kernel@...r.kernel.org,
        virtualization@...ts.linux-foundation.org, linux-mm@...ck.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...e.com>,
        "Michael S . Tsirkin" <mst@...hat.com>
Subject: Re: [PATCH v1 1/6] mm/page_alloc: tweak comments in
 has_unmovable_pages()

On 07/28/20 at 04:07pm, David Hildenbrand wrote:
> On 28.07.20 15:48, Baoquan He wrote:
> > On 06/30/20 at 04:26pm, David Hildenbrand wrote:
> >> Let's move the split comment regarding bootmem allocations and memory
> >> holes, especially in the context of ZONE_MOVABLE, to the PageReserved()
> >> check.
> >>
> >> Cc: Andrew Morton <akpm@...ux-foundation.org>
> >> Cc: Michal Hocko <mhocko@...e.com>
> >> Cc: Michael S. Tsirkin <mst@...hat.com>
> >> Signed-off-by: David Hildenbrand <david@...hat.com>
> >> ---
> >>  mm/page_alloc.c | 22 ++++++----------------
> >>  1 file changed, 6 insertions(+), 16 deletions(-)
> >>
> >> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> >> index 48eb0f1410d47..bd3ebf08f09b9 100644
> >> --- a/mm/page_alloc.c
> >> +++ b/mm/page_alloc.c
> >> @@ -8207,14 +8207,6 @@ struct page *has_unmovable_pages(struct zone *zone, struct page *page,
> >>  	unsigned long iter = 0;
> >>  	unsigned long pfn = page_to_pfn(page);
> >>  
> >> -	/*
> >> -	 * TODO we could make this much more efficient by not checking every
> >> -	 * page in the range if we know all of them are in MOVABLE_ZONE and
> >> -	 * that the movable zone guarantees that pages are migratable but
> >> -	 * the later is not the case right now unfortunatelly. E.g. movablecore
> >> -	 * can still lead to having bootmem allocations in zone_movable.
> >> -	 */
> >> -
> >>  	if (is_migrate_cma_page(page)) {
> >>  		/*
> >>  		 * CMA allocations (alloc_contig_range) really need to mark
> >> @@ -8233,6 +8225,12 @@ struct page *has_unmovable_pages(struct zone *zone, struct page *page,
> >>  
> >>  		page = pfn_to_page(pfn + iter);
> >>  
> >> +		/*
> >> +		 * Both, bootmem allocations and memory holes are marked
> >> +		 * PG_reserved and are unmovable. We can even have unmovable
> >> +		 * allocations inside ZONE_MOVABLE, for example when
> >> +		 * specifying "movable_core".
> >                                ~~~~ should be 'movablecore', we don't
> > have kernel parameter 'movable_core'.
> 
> Agreed!
> 
> > 
> > Otherwise, this looks good to me. Esp the code comment at below had been
> > added very long time ago and obsolete.
> > 
> > Reviewed-by: Baoquan He <bhe@...hat.com>
> > 
> > By the way, David, do you know what is the situation of having unmovable
> > allocations inside ZONE_MOVABLE when specifying 'movablecore'? I quickly
> > went through find_zone_movable_pfns_for_nodes(), but didn't get why.
> > Could you tell a little more detail about it?
> 
> As far as I understand, it can happen that we have memblock allocations
> during boot that fall into an area the kernel later configures to span
> the movable zone (via movable_core).

Seems yes, thanks a lot. Wondering who is still using
movablecore|kernelcore in what use case.