From: Minchan Kim <minchan@kernel.org>
To: David Hildenbrand <david@redhat.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>,
John Hubbard <jhubbard@nvidia.com>,
Andrew Morton <akpm@linux-foundation.org>,
syzbot <syzbot+acf65ca584991f3cc447@syzkaller.appspotmail.com>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org,
llvm@lists.linux.dev, nathan@kernel.org, ndesaulniers@google.com,
syzkaller-bugs@googlegroups.com, trix@redhat.com,
Matthew Wilcox <willy@infradead.org>,
Stephen Rothwell <sfr@canb.auug.org.au>
Subject: Re: [syzbot] WARNING in follow_hugetlb_page
Date: Sat, 21 May 2022 11:25:00 -0700 [thread overview]
Message-ID: <YokufHxnkHUk5UR6@google.com> (raw)
In-Reply-To: <000a117a-694d-d3a9-a192-14d08d50c884@redhat.com>
On Sat, May 21, 2022 at 06:46:27PM +0200, David Hildenbrand wrote:
< snip >
> >> The general rules are:
> >>
> >> ZONE_MOVABLE: nobody is allowed to place unmovable allocations there; it
> >> could prevent memory offlining/unplug.
> >>
> >> CMA: nobody *but the designated owner* is allowed to place unmovable
> >> memory there; it could prevent the actual owner to allocate contiguous
> >> memory.
> >
> > I am confused what's the meaning of designated owner and actuall owner
> > in your context.
>
> designated==actual here. I just wanted to distinguish from someone
> current temporary owner of the page ("allocated it via a movable
> allocation") but the actual designated owner (e.g., hugetlb CMA)
>
> The page/memory owner terminology is just confusing. Let's rephrase to:
> only the CMA area owner is allowed to place unmovable allocations there.
Yeah, the CMA area owner is much better.
>
> >
> > What I thought about the issue based on you explanation:
> >
> > HugeTLB allocates its page by two types of allocation
> >
> > 1. alloc_pages(GFP_MOVABLE)
> >
> > It could allocate the hugetlb page from CMA area but longterm pin
> > should migrate them out of cma before the pinning so allowing
> > the pinning on the page is no problem and current code works like
> > that.
> >
> > check_and_migrate_movable_pages
> >
>
> Yes.
>
> > 2. cma_alloc
> >
> > The cma_alloc is used only for *gigantic page* and the hugetlbfs
> > is the very owner of the page. IOW, if the hugetlbfs was succeeded
> > to allocate the gigantic page by cma_alloc, there is no other
> > owner to be able to claim the page any longer so it's fine to
> > allow longterm pinning againt the gingantic page but current.
> > However, current code doesn't work like that due to
> > is_pinnable_page. IOW, hugetlbfs need a way to distinguish
> > whether the page owner is hugetlbfs or not.
> >
> > Are we on same page?
>
> Yes, exactly. What I wanted to express is: for huge pages we have to
> make a smarter decision because there are cases where we want to
> migrate, and cases where we don't want to migrate.
Sure, maybe hugetlbfs could squeeze a bit in one of subpage of the
CMA compound page. "I am CMA allocated but allow to pinned for longterm"
Thanks.
next prev parent reply other threads:[~2022-05-21 18:25 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-05-13 9:03 [syzbot] WARNING in follow_hugetlb_page syzbot
2022-05-13 16:43 ` syzbot
2022-05-13 17:26 ` Andrew Morton
2022-05-13 18:09 ` Mike Kravetz
2022-05-13 22:48 ` Mike Kravetz
2022-05-13 23:19 ` Andrew Morton
2022-05-13 23:54 ` Minchan Kim
2022-05-14 0:09 ` John Hubbard
2022-05-14 0:26 ` Minchan Kim
2022-05-14 0:56 ` John Hubbard
2022-05-14 1:16 ` John Hubbard
2022-05-17 3:37 ` Mike Kravetz
2022-05-18 7:12 ` John Hubbard
2022-05-20 22:19 ` Minchan Kim
2022-05-20 22:56 ` John Hubbard
2022-05-20 23:25 ` Minchan Kim
2022-05-20 23:31 ` Mike Kravetz
2022-05-20 23:43 ` Minchan Kim
2022-05-21 0:04 ` Mike Kravetz
2022-05-21 15:24 ` Minchan Kim
2022-05-21 15:51 ` David Hildenbrand
2022-05-21 16:36 ` Minchan Kim
2022-05-21 16:46 ` David Hildenbrand
2022-05-21 18:25 ` Minchan Kim [this message]
2022-05-21 23:50 ` Mike Kravetz
2022-05-14 0:18 ` Andrew Morton
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