From: Oscar Salvador <osalvador@suse.de>
To: David Hildenbrand <david@redhat.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>,
Muchun Song <songmuchun@bytedance.com>,
Michal Hocko <mhocko@kernel.org>,
linux-mm@kvack.org, linux-kernel@vger.kernel.org
Subject: Re: [RFC PATCH 1/2] mm,page_alloc: Make alloc_contig_range handle in-use hugetlb pages
Date: Wed, 10 Feb 2021 15:14:25 +0100 [thread overview]
Message-ID: <20210210141425.GB3636@localhost.localdomain> (raw)
In-Reply-To: <d38527b5-140d-15e5-c1c4-f381602eab46@redhat.com>
On Wed, Feb 10, 2021 at 03:11:05PM +0100, David Hildenbrand wrote:
> On 10.02.21 15:09, Oscar Salvador wrote:
> > On Wed, Feb 10, 2021 at 09:56:37AM +0100, David Hildenbrand wrote:
> > > On 08.02.21 11:38, Oscar Salvador wrote:
> > > > alloc_contig_range is not prepared to handle hugetlb pages and will
> > > > fail if it ever sees one, but since they can be migrated as any other
> > > > page (LRU and Movable), it makes sense to also handle them.
> > > >
> > > > For now, do it only when coming from alloc_contig_range.
> > > >
> > > > Signed-off-by: Oscar Salvador <osalvador@suse.de>
> > > > ---
> > > > mm/compaction.c | 17 +++++++++++++++++
> > > > mm/vmscan.c | 5 +++--
> > > > 2 files changed, 20 insertions(+), 2 deletions(-)
> > > >
> > > > diff --git a/mm/compaction.c b/mm/compaction.c
> > > > index e5acb9714436..89cd2e60da29 100644
> > > > --- a/mm/compaction.c
> > > > +++ b/mm/compaction.c
> > > > @@ -940,6 +940,22 @@ isolate_migratepages_block(struct compact_control *cc, unsigned long low_pfn,
> > > > goto isolate_fail;
> > > > }
> > > > + /*
> > > > + * Handle hugetlb pages only when coming from alloc_contig
> > > > + */
> > > > + if (PageHuge(page) && cc->alloc_contig) {
> > > > + if (page_count(page)) {
> > >
> > > I wonder if we should care about races here. What if someone concurrently
> > > allocates/frees?
> > >
> > > Note that PageHuge() succeeds on tail pages, isolate_huge_page() not, i
> > > assume we'll have to handle that as well.
> > >
> > > I wonder if it would make sense to move some of the magic to hugetlb code
> > > and handle it there with less chances for races (isolate if used,
> > > alloc-and-dissolve if not).
> >
> > Yes, it makes sense to keep the magic in hugetlb code.
> > Note, though, that removing all races might be tricky.
> >
> > isolate_huge_page() checks for PageHuge under hugetlb_lock,
> > so there is a race between a call to PageHuge(x) and a subsequent
> > call to isolate_huge_page().
> > But we should be fine as isolate_huge_page will fail in case the page is
> > no longer HugeTLB.
> >
> > Also, since isolate_migratepages_block() gets called with ranges
> > pageblock aligned, we should never be handling tail pages in the core
> > of the function. E.g: the same way we handle THP:
>
> Gigantic pages? (spoiler: see my comments to next patch :) )
Oh, yeah, that sucks.
We had the same problem in scan_movable_pages/has_unmovable_pages
with such pages.
Uhm, I will try to be more careful :-)
--
Oscar Salvador
SUSE L3
next prev parent reply other threads:[~2021-02-10 14:14 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-02-08 10:38 [RFC PATCH 0/2] Make alloc_contig_range handle Hugetlb pages Oscar Salvador
2021-02-08 10:38 ` [RFC PATCH 1/2] mm,page_alloc: Make alloc_contig_range handle in-use hugetlb pages Oscar Salvador
2021-02-10 8:56 ` David Hildenbrand
2021-02-10 14:09 ` Oscar Salvador
2021-02-10 14:11 ` David Hildenbrand
2021-02-10 14:14 ` Oscar Salvador [this message]
2021-02-10 14:22 ` David Hildenbrand
2021-02-11 0:56 ` Mike Kravetz
2021-02-11 10:40 ` David Hildenbrand
2021-02-08 10:38 ` [RFC PATCH 2/2] mm,page_alloc: Make alloc_contig_range handle free " Oscar Salvador
2021-02-10 8:23 ` David Hildenbrand
2021-02-10 14:24 ` Oscar Salvador
2021-02-10 14:36 ` David Hildenbrand
2021-02-25 21:43 ` Mike Kravetz
2021-02-25 22:15 ` David Hildenbrand
2021-02-11 1:16 ` Mike Kravetz
2021-02-11 21:38 ` Oscar Salvador
2021-02-08 10:39 ` [RFC PATCH 0/2] Make alloc_contig_range handle Hugetlb pages Oscar Salvador
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