From: Muchun Song <songmuchun@bytedance.com>
To: David Hildenbrand <david@redhat.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>,
Andrew Morton <akpm@linux-foundation.org>,
Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>,
Andi Kleen <ak@linux.intel.com>,
mhocko@suse.cz,
Linux Memory Management List <linux-mm@kvack.org>,
LKML <linux-kernel@vger.kernel.org>,
Yang Shi <shy828301@gmail.com>
Subject: Re: [External] Re: [PATCH v3 1/6] mm: migrate: do not migrate HugeTLB page whose refcount is one
Date: Tue, 12 Jan 2021 21:40:07 +0800 [thread overview]
Message-ID: <CAMZfGtWnATsqgdqVONgAFWAAJU=KGxVJQEt38b8JTV+UtRzkYw@mail.gmail.com> (raw)
In-Reply-To: <c6eddfc6-8e15-4a28-36ff-64bfa65cca8e@redhat.com>
On Tue, Jan 12, 2021 at 7:11 PM David Hildenbrand <david@redhat.com> wrote:
>
> On 12.01.21 12:00, David Hildenbrand wrote:
> > On 10.01.21 13:40, Muchun Song wrote:
> >> If the refcount is one when it is migrated, it means that the page
> >> was freed from under us. So we are done and do not need to migrate.
> >>
> >> This optimization is consistent with the regular pages, just like
> >> unmap_and_move() does.
> >>
> >> Signed-off-by: Muchun Song <songmuchun@bytedance.com>
> >> Reviewed-by: Mike Kravetz <mike.kravetz@oracle.com>
> >> Acked-by: Yang Shi <shy828301@gmail.com>
> >> ---
> >> mm/migrate.c | 6 ++++++
> >> 1 file changed, 6 insertions(+)
> >>
> >> diff --git a/mm/migrate.c b/mm/migrate.c
> >> index 4385f2fb5d18..a6631c4eb6a6 100644
> >> --- a/mm/migrate.c
> >> +++ b/mm/migrate.c
> >> @@ -1279,6 +1279,12 @@ static int unmap_and_move_huge_page(new_page_t get_new_page,
> >> return -ENOSYS;
> >> }
> >>
> >> + if (page_count(hpage) == 1) {
> >> + /* page was freed from under us. So we are done. */
> >> + putback_active_hugepage(hpage);
> >> + return MIGRATEPAGE_SUCCESS;
> >> + }
> >> +
> >> new_hpage = get_new_page(hpage, private);
> >> if (!new_hpage)
> >> return -ENOMEM;
> >>
> >
> > Question: What if called via alloc_contig_range() where we even want to
> > "migrate" free pages, meaning, relocate it?
> >
>
> To be more precise:
>
> a) We don't have dissolve_free_huge_pages() calls on the
> alloc_contig_range() path. So we *need* migration IIUC.
Without this patch, if you want to migrate a HUgeTLB page,
the page is freed to the hugepage pool. With this patch,
the page is also freed to the hugepage pool.
I didn't see any different. I am missing something?
>
> b) dissolve_free_huge_pages() will fail if going below the reservation.
> In that case we really want to migrate free pages. This even applies to
> memory offlining.
>
> Either I am missing something important or this patch is more dangerous
> than it looks like.
>
> --
> Thanks,
>
> David / dhildenb
>
next prev parent reply other threads:[~2021-01-12 13:40 UTC|newest]
Thread overview: 39+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-10 12:40 [PATCH v3 0/6] Fix some bugs about HugeTLB code Muchun Song
2021-01-10 12:40 ` [PATCH v3 1/6] mm: migrate: do not migrate HugeTLB page whose refcount is one Muchun Song
2021-01-12 9:42 ` Michal Hocko
2021-01-12 9:43 ` [External] " Muchun Song
2021-01-12 11:00 ` David Hildenbrand
2021-01-12 11:11 ` David Hildenbrand
2021-01-12 11:27 ` Michal Hocko
2021-01-12 11:34 ` David Hildenbrand
2021-01-12 12:16 ` Michal Hocko
2021-01-12 14:23 ` Michal Hocko
2021-01-12 14:41 ` David Hildenbrand
2021-01-12 14:53 ` Michal Hocko
2021-01-12 20:12 ` Mike Kravetz
2021-01-12 13:40 ` Muchun Song [this message]
2021-01-12 13:51 ` [External] " David Hildenbrand
2021-01-12 14:17 ` Muchun Song
2021-01-12 14:28 ` David Hildenbrand
2021-01-12 14:59 ` Muchun Song
2021-01-10 12:40 ` [PATCH v3 2/6] mm: hugetlbfs: fix cannot migrate the fallocated HugeTLB page Muchun Song
2021-01-11 23:04 ` Mike Kravetz
2021-01-12 9:45 ` Michal Hocko
2021-01-10 12:40 ` [PATCH v3 3/6] mm: hugetlb: fix a race between freeing and dissolving the page Muchun Song
2021-01-12 1:06 ` Mike Kravetz
2021-01-12 10:02 ` Michal Hocko
2021-01-12 10:13 ` [External] " Muchun Song
2021-01-12 11:17 ` Michal Hocko
2021-01-12 11:43 ` Muchun Song
2021-01-12 12:37 ` Michal Hocko
2021-01-12 15:05 ` Muchun Song
2021-01-10 12:40 ` [PATCH v3 4/6] mm: hugetlb: add return -EAGAIN for dissolve_free_huge_page Muchun Song
2021-01-12 1:20 ` Mike Kravetz
2021-01-12 8:33 ` Michal Hocko
2021-01-12 9:51 ` [External] " Muchun Song
2021-01-12 10:06 ` Michal Hocko
2021-01-12 10:49 ` Muchun Song
2021-01-12 11:11 ` Michal Hocko
2021-01-12 11:34 ` Muchun Song
2021-01-10 12:40 ` [PATCH v3 5/6] mm: hugetlb: fix a race between isolating and freeing page Muchun Song
2021-01-10 12:40 ` [PATCH v3 6/6] mm: hugetlb: remove VM_BUG_ON_PAGE from page_huge_active Muchun Song
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