From: Matthew Wilcox <willy@infradead.org>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: David Hildenbrand <david@redhat.com>,
Nadav Amit <namit@vmware.com>, Jason Gunthorpe <jgg@nvidia.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
Hugh Dickins <hughd@google.com>,
David Rientjes <rientjes@google.com>,
Shakeel Butt <shakeelb@google.com>,
John Hubbard <jhubbard@nvidia.com>,
Mike Kravetz <mike.kravetz@oracle.com>,
Mike Rapoport <rppt@linux.ibm.com>,
Yang Shi <shy828301@gmail.com>,
"Kirill A . Shutemov" <kirill.shutemov@linux.intel.com>,
Vlastimil Babka <vbabka@suse.cz>, Jann Horn <jannh@google.com>,
Michal Hocko <mhocko@kernel.org>, Rik van Riel <riel@surriel.com>,
Roman Gushchin <guro@fb.com>,
Andrea Arcangeli <aarcange@redhat.com>,
Peter Xu <peterx@redhat.com>, Donald Dutile <ddutile@redhat.com>,
Christoph Hellwig <hch@lst.de>, Oleg Nesterov <oleg@redhat.com>,
Jan Kara <jack@suse.cz>, Linux-MM <linux-mm@kvack.org>,
"open list:KERNEL SELFTEST FRAMEWORK"
<linux-kselftest@vger.kernel.org>,
"open list:DOCUMENTATION" <linux-doc@vger.kernel.org>
Subject: Re: [PATCH v1 06/11] mm: support GUP-triggered unsharing via FAULT_FLAG_UNSHARE (!hugetlb)
Date: Sun, 19 Dec 2021 22:02:01 +0000 [thread overview]
Message-ID: <Yb+r2W6RCKhO5toC@casper.infradead.org> (raw)
In-Reply-To: <CAHk-=wgLLRT_KeM5Se1AxGcf-g5MkCS-JmPy169Rpdeky_YkXg@mail.gmail.com>
On Sun, Dec 19, 2021 at 01:53:36PM -0800, Linus Torvalds wrote:
> On Sun, Dec 19, 2021 at 1:48 PM Matthew Wilcox <willy@infradead.org> wrote:
> >
> > Yes, agreed, I was thinking that we could use "not mapped at all"
> > as an optimisation to avoid doing rmap walks. eg __unmap_and_move().
>
> So the thing is, it's a very dodgy optimization for a rather simple
> reason: what if somebody pages the page in?
>
> So even "not mapped at all" is questionable.
>
> You have to check that it's also not a swapcache page, and hold the
> page lock for that check, at the very least.
>
> And by then, you're really in a very unusual situation - and my gut
> feel says not one worth optimizing for (because anon pages are
> _usually_ mapped at least once).
I'd like to get rid of ->mapcount for file pages too. And those are
definitely never mapped in the majority of cases.
next prev parent reply other threads:[~2021-12-19 22:03 UTC|newest]
Thread overview: 127+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-12-17 11:30 [PATCH v1 00/11] mm: COW fixes part 1: fix the COW security issue for THP and hugetlb David Hildenbrand
2021-12-17 11:30 ` [PATCH v1 01/11] seqlock: provide lockdep-free raw_seqcount_t variant David Hildenbrand
2021-12-17 17:02 ` Nadav Amit
2021-12-17 17:29 ` David Hildenbrand
2021-12-17 17:49 ` David Hildenbrand
2021-12-17 18:01 ` Nadav Amit
2021-12-17 21:28 ` Thomas Gleixner
2021-12-17 22:02 ` David Hildenbrand
2021-12-17 11:30 ` [PATCH v1 02/11] mm: thp: consolidate mapcount logic on THP split David Hildenbrand
2021-12-17 19:06 ` Yang Shi
2021-12-18 14:24 ` Kirill A. Shutemov
2021-12-17 11:30 ` [PATCH v1 03/11] mm: simplify hugetlb and file-THP handling in __page_mapcount() David Hildenbrand
2021-12-17 17:16 ` Nadav Amit
2021-12-17 17:30 ` David Hildenbrand
2021-12-17 18:06 ` Mike Kravetz
2021-12-17 18:11 ` David Hildenbrand
2021-12-17 19:07 ` Yang Shi
2021-12-18 14:31 ` Kirill A. Shutemov
2021-12-17 11:30 ` [PATCH v1 04/11] mm: thp: simlify total_mapcount() David Hildenbrand
2021-12-17 19:12 ` Yang Shi
2021-12-18 14:35 ` Kirill A. Shutemov
2021-12-17 11:30 ` [PATCH v1 05/11] mm: thp: allow for reading the THP mapcount atomically via a raw_seqlock_t David Hildenbrand
2021-12-17 11:30 ` [PATCH v1 06/11] mm: support GUP-triggered unsharing via FAULT_FLAG_UNSHARE (!hugetlb) David Hildenbrand
2021-12-17 19:04 ` Linus Torvalds
2021-12-17 19:22 ` Linus Torvalds
2021-12-17 20:17 ` David Hildenbrand
2021-12-17 20:36 ` Linus Torvalds
2021-12-17 20:39 ` Linus Torvalds
2021-12-17 20:43 ` Linus Torvalds
2021-12-17 20:42 ` David Hildenbrand
2021-12-17 20:45 ` Linus Torvalds
2021-12-18 22:52 ` Kirill A. Shutemov
2021-12-18 23:05 ` Linus Torvalds
2021-12-17 20:47 ` Jason Gunthorpe
2021-12-17 20:56 ` Linus Torvalds
2021-12-17 21:17 ` David Hildenbrand
2021-12-17 21:04 ` David Hildenbrand
2021-12-18 0:50 ` Jason Gunthorpe
2021-12-17 21:15 ` Nadav Amit
2021-12-17 21:20 ` David Hildenbrand
2021-12-18 0:50 ` Jason Gunthorpe
2021-12-18 1:53 ` Linus Torvalds
2021-12-18 2:17 ` Linus Torvalds
2021-12-18 2:42 ` Linus Torvalds
2021-12-18 3:36 ` Linus Torvalds
2021-12-18 3:05 ` Jason Gunthorpe
2021-12-18 3:30 ` Nadav Amit
2021-12-18 3:38 ` Linus Torvalds
2021-12-18 18:42 ` Jason Gunthorpe
2021-12-18 21:48 ` Nadav Amit
2021-12-18 22:53 ` Linus Torvalds
2021-12-19 0:19 ` Nadav Amit
2021-12-19 0:35 ` Linus Torvalds
2021-12-19 6:02 ` Nadav Amit
2021-12-19 8:01 ` John Hubbard
2021-12-19 11:30 ` Matthew Wilcox
2021-12-19 17:27 ` Linus Torvalds
2021-12-19 17:44 ` David Hildenbrand
2021-12-19 17:44 ` Linus Torvalds
2021-12-19 17:59 ` David Hildenbrand
2021-12-19 21:12 ` Matthew Wilcox
2021-12-19 21:27 ` Linus Torvalds
2021-12-19 21:47 ` Matthew Wilcox
2021-12-19 21:53 ` Linus Torvalds
2021-12-19 22:02 ` Matthew Wilcox [this message]
2021-12-19 22:12 ` Linus Torvalds
2021-12-19 22:26 ` Matthew Wilcox
2021-12-20 18:37 ` Matthew Wilcox
2021-12-20 18:52 ` Matthew Wilcox
2021-12-20 19:38 ` Linus Torvalds
2021-12-20 19:15 ` Linus Torvalds
2021-12-20 21:02 ` Matthew Wilcox
2021-12-20 21:27 ` Linus Torvalds
2021-12-21 1:03 ` Jason Gunthorpe
2021-12-21 3:29 ` Matthew Wilcox
2021-12-21 8:58 ` David Hildenbrand
2021-12-21 14:28 ` Jason Gunthorpe
[not found] ` <303f21d3-42b4-2f11-3f22-28f89f819080@redhat.com>
2021-12-21 23:54 ` Jason Gunthorpe
2021-12-21 17:05 ` Linus Torvalds
2021-12-21 17:40 ` David Hildenbrand
2021-12-21 18:00 ` Linus Torvalds
[not found] ` <dda021c8-69ec-c660-46be-793ae345a5bb@redhat.com>
2021-12-21 21:11 ` John Hubbard
2021-12-21 18:07 ` Jan Kara
2021-12-21 18:30 ` Linus Torvalds
[not found] ` <d23ede12-5df7-2f28-00fd-ea58d85ae400@redhat.com>
2021-12-21 18:58 ` Linus Torvalds
2021-12-21 21:16 ` John Hubbard
2021-12-21 19:07 ` Jason Gunthorpe
[not found] ` <3e0868e6-c714-1bf8-163f-389989bf5189@redhat.com>
[not found] ` <dfe1c8d5-6fac-9040-0272-6d77bafa6a16@redhat.com>
2021-12-22 12:41 ` Jan Kara
[not found] ` <4a28e8a0-2efa-8b5e-10b5-38f1fc143a98@redhat.com>
2021-12-22 14:42 ` Jan Kara
[not found] ` <505d3d0f-23ee-0eec-0571-8058b8eedb97@redhat.com>
2021-12-22 16:08 ` Jan Kara
2021-12-22 16:44 ` Matthew Wilcox
2021-12-22 18:40 ` Linus Torvalds
2021-12-23 12:54 ` Jan Kara
2021-12-23 17:18 ` Linus Torvalds
2021-12-23 0:21 ` Matthew Wilcox
2021-12-24 2:53 ` Jason Gunthorpe
2021-12-24 4:53 ` Matthew Wilcox
2022-01-04 0:33 ` Jason Gunthorpe
2021-12-21 23:59 ` Jason Gunthorpe
2021-12-22 12:44 ` Jan Kara
2021-12-17 20:45 ` David Hildenbrand
2021-12-17 20:51 ` Linus Torvalds
2021-12-17 20:55 ` David Hildenbrand
2021-12-17 21:36 ` Linus Torvalds
2021-12-17 21:47 ` David Hildenbrand
2021-12-17 21:50 ` Linus Torvalds
2021-12-17 22:29 ` David Hildenbrand
2021-12-17 22:58 ` Linus Torvalds
2021-12-17 23:29 ` David Hildenbrand
2021-12-17 23:53 ` Nadav Amit
2021-12-18 4:02 ` Linus Torvalds
2021-12-18 4:52 ` Nadav Amit
2021-12-18 5:03 ` Matthew Wilcox
2021-12-18 5:23 ` Nadav Amit
2021-12-18 18:37 ` Linus Torvalds
2021-12-17 22:18 ` Linus Torvalds
2021-12-17 22:43 ` David Hildenbrand
2021-12-17 23:20 ` Linus Torvalds
2021-12-18 9:57 ` David Hildenbrand
2021-12-18 19:21 ` Linus Torvalds
2021-12-18 19:52 ` Linus Torvalds
2021-12-19 8:43 ` David Hildenbrand
2021-12-17 11:30 ` [PATCH v1 07/11] mm: gup: trigger unsharing via FAULT_FLAG_UNSHARE when required (!hugetlb) David Hildenbrand
2021-12-17 11:30 ` [PATCH v1 08/11] mm: hugetlb: support GUP-triggered unsharing via FAULT_FLAG_UNSHARE David Hildenbrand
2021-12-17 11:30 ` [PATCH v1 09/11] mm: gup: trigger unsharing via FAULT_FLAG_UNSHARE when required (hugetlb) David Hildenbrand
2021-12-17 11:30 ` [PATCH v1 10/11] mm: thp: introduce and use page_trans_huge_anon_shared() David Hildenbrand
2021-12-17 11:30 ` [PATCH v1 11/11] selftests/vm: add tests for the known COW security issues David Hildenbrand
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