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From: Peter Xu <peterx@redhat.com>
To: linux-mm@kvack.org, linux-kernel@vger.kernel.org
Cc: Jason Gunthorpe <jgg@ziepe.ca>,
	Andrew Morton <akpm@linux-foundation.org>,
	Jan Kara <jack@suse.cz>, Michal Hocko <mhocko@suse.com>,
	Kirill Tkhai <ktkhai@virtuozzo.com>,
	Kirill Shutemov <kirill@shutemov.name>,
	Hugh Dickins <hughd@google.com>, Peter Xu <peterx@redhat.com>,
	Christoph Hellwig <hch@lst.de>,
	Andrea Arcangeli <aarcange@redhat.com>,
	John Hubbard <jhubbard@nvidia.com>,
	Oleg Nesterov <oleg@redhat.com>,
	Leon Romanovsky <leonro@nvidia.com>,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Jann Horn <jannh@google.com>
Subject: [PATCH 0/5] mm: Break COW for pinned pages during fork()
Date: Mon, 21 Sep 2020 17:17:39 -0400	[thread overview]
Message-ID: <20200921211744.24758-1-peterx@redhat.com> (raw)

Finally I start to post formal patches because it's growing.  And also since
we've discussed quite some issues already, so I feel like it's clearer on what
we need to do, and how.

This series is majorly inspired by the previous discussion on the list [1],
starting from the report from Jason on the rdma test failure.  Linus proposed
the solution, which seems to be a very nice approach to avoid the breakage of
userspace apps that didn't use MADV_DONTFORK properly before.  More information
can be found in that thread too.

I believe the initial plan was to consider merging something like this for
rc7/rc8.  However now I'm not sure due to the fact that the code change in
copy_pte_range() is probably more than expected, so it can be with some risk.
I'll leave this question to the reviewers...

I tested it myself with fork() after vfio pinning a bunch of device pages, and
I verified that the new copy pte logic worked as expected at least in the most
general path.  However I didn't test thp case yet because afaict vfio does not
support thp backed dma pages.  Luckily, the pmd/pud thp patch is much more
straightforward than the pte one, so hopefully it can be directly verified by
some code review plus some more heavy-weight rdma tests.

Patch 1:      Introduce mm.has_pinned (as single patch as suggested by Jason)
Patch 2-3:    Some slight rework on copy_page_range() path as preparation
Patch 4:      Early cow solution for pte copy for pinned pages
Patch 5:      Same as above, but for thp (pmd/pud).

Hugetlbfs fix is still missing, but as planned, that's not urgent so we can
work upon.  Comments greatly welcomed.

Thanks.

Peter Xu (5):
  mm: Introduce mm_struct.has_pinned
  mm/fork: Pass new vma pointer into copy_page_range()
  mm: Rework return value for copy_one_pte()
  mm: Do early cow for pinned pages during fork() for ptes
  mm/thp: Split huge pmds/puds if they're pinned when fork()

 include/linux/mm.h       |   2 +-
 include/linux/mm_types.h |  10 ++
 kernel/fork.c            |   3 +-
 mm/gup.c                 |   6 ++
 mm/huge_memory.c         |  26 +++++
 mm/memory.c              | 226 +++++++++++++++++++++++++++++++++++----
 6 files changed, 248 insertions(+), 25 deletions(-)

-- 
2.26.2




             reply	other threads:[~2020-09-21 21:17 UTC|newest]

Thread overview: 110+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-21 21:17 Peter Xu [this message]
2020-09-21 21:17 ` [PATCH 1/5] mm: Introduce mm_struct.has_pinned Peter Xu
2020-09-21 21:43   ` Jann Horn
2020-09-21 22:30     ` Peter Xu
2020-09-21 22:47       ` Jann Horn
2020-09-22 11:54         ` Jason Gunthorpe
2020-09-22 14:28           ` Peter Xu
2020-09-22 15:56             ` Jason Gunthorpe
2020-09-22 16:25               ` Linus Torvalds
2020-09-21 23:53   ` John Hubbard
2020-09-22  0:01     ` John Hubbard
2020-09-22 15:17     ` Peter Xu
2020-09-22 16:10       ` Jason Gunthorpe
2020-09-22 17:54         ` Peter Xu
2020-09-22 19:11           ` Jason Gunthorpe
2020-09-23  0:27             ` Peter Xu
2020-09-23 13:10               ` Peter Xu
2020-09-23 14:20                 ` Jan Kara
2020-09-23 17:12                   ` Jason Gunthorpe
2020-09-24  7:44                     ` Jan Kara
2020-09-24 14:02                       ` Jason Gunthorpe
2020-09-24 14:45                         ` Jan Kara
2020-09-23 17:07               ` Jason Gunthorpe
2020-09-24 14:35                 ` Peter Xu
2020-09-24 16:51                   ` Jason Gunthorpe
2020-09-24 17:55                     ` Peter Xu
2020-09-24 18:15                       ` Jason Gunthorpe
2020-09-24 18:34                         ` Peter Xu
2020-09-24 18:39                           ` Jason Gunthorpe
2020-09-24 21:30                             ` Peter Xu
2020-09-25 19:56                               ` Linus Torvalds
2020-09-25 21:06                                 ` Linus Torvalds
2020-09-26  0:41                                   ` Jason Gunthorpe
2020-09-26  1:15                                     ` Linus Torvalds
2020-09-26 22:28                                       ` Linus Torvalds
2020-09-27  6:23                                         ` Leon Romanovsky
2020-09-27 18:16                                           ` Linus Torvalds
2020-09-27 18:45                                             ` Linus Torvalds
2020-09-28 12:49                                               ` Jason Gunthorpe
2020-09-28 16:17                                                 ` Linus Torvalds
2020-09-28 17:22                                                   ` Peter Xu
2020-09-28 17:54                                                     ` Linus Torvalds
2020-09-28 18:39                                                       ` Jason Gunthorpe
2020-09-28 19:29                                                         ` Linus Torvalds
2020-09-28 23:57                                                           ` Jason Gunthorpe
2020-09-29  0:18                                                             ` John Hubbard
2020-09-28 19:36                                                         ` Linus Torvalds
2020-09-28 19:50                                                           ` Linus Torvalds
2020-09-28 22:51                                                             ` Jason Gunthorpe
2020-09-29  0:30                                                               ` Peter Xu
2020-10-08  5:49                                                             ` Leon Romanovsky
2020-09-28 17:13                                             ` Peter Xu
2020-09-25 21:13                                 ` Peter Xu
2020-09-25 22:08                                   ` Linus Torvalds
2020-09-22 18:02       ` John Hubbard
2020-09-22 18:15         ` Peter Xu
2020-09-22 19:11       ` John Hubbard
2020-09-27  0:41   ` [mm] 698ac7610f: will-it-scale.per_thread_ops 8.2% improvement kernel test robot
2020-09-21 21:17 ` [PATCH 2/5] mm/fork: Pass new vma pointer into copy_page_range() Peter Xu
2020-09-21 21:17 ` [PATCH 3/5] mm: Rework return value for copy_one_pte() Peter Xu
2020-09-22  7:11   ` John Hubbard
2020-09-22 15:29     ` Peter Xu
2020-09-22 10:08   ` Oleg Nesterov
2020-09-22 10:18     ` Oleg Nesterov
2020-09-22 15:36       ` Peter Xu
2020-09-22 15:48         ` Oleg Nesterov
2020-09-22 16:03           ` Peter Xu
2020-09-22 16:53             ` Oleg Nesterov
2020-09-22 18:13               ` Peter Xu
2020-09-22 18:23                 ` Oleg Nesterov
2020-09-22 18:49                   ` Peter Xu
2020-09-23  6:52                     ` Oleg Nesterov
2020-09-23 17:16   ` Linus Torvalds
2020-09-23 21:24     ` Linus Torvalds
2020-09-21 21:20 ` [PATCH 4/5] mm: Do early cow for pinned pages during fork() for ptes Peter Xu
2020-09-21 21:55   ` Jann Horn
2020-09-21 22:18     ` John Hubbard
2020-09-21 22:27       ` Jann Horn
2020-09-22  0:08         ` John Hubbard
2020-09-21 22:27     ` Peter Xu
2020-09-22 11:48   ` Oleg Nesterov
2020-09-22 12:40     ` Oleg Nesterov
2020-09-22 15:58       ` Peter Xu
2020-09-22 16:52         ` Oleg Nesterov
2020-09-22 18:34           ` Peter Xu
2020-09-22 18:44             ` Oleg Nesterov
2020-09-23  1:03               ` Peter Xu
2020-09-23 20:25                 ` Linus Torvalds
2020-09-24 15:08                   ` Peter Xu
2020-09-24 11:48   ` Kirill Tkhai
2020-09-24 15:16     ` Peter Xu
2020-09-21 21:20 ` [PATCH 5/5] mm/thp: Split huge pmds/puds if they're pinned when fork() Peter Xu
2020-09-22  6:41   ` John Hubbard
2020-09-22 10:33     ` Jan Kara
2020-09-22 20:01       ` John Hubbard
2020-09-23  9:22         ` Jan Kara
2020-09-23 13:50           ` Peter Xu
2020-09-23 14:01             ` Jan Kara
2020-09-23 15:44               ` Peter Xu
2020-09-23 20:19                 ` John Hubbard
2020-09-24 18:49                   ` Peter Xu
2020-09-23 16:06     ` Peter Xu
2020-09-22 12:05   ` Jason Gunthorpe
2020-09-23 15:24     ` Peter Xu
2020-09-23 16:07       ` Yang Shi
2020-09-24 15:47         ` Peter Xu
2020-09-24 17:29           ` Yang Shi
2020-09-23 17:17       ` Jason Gunthorpe
2020-09-23 10:21 ` [PATCH 0/5] mm: Break COW for pinned pages during fork() Leon Romanovsky
2020-09-23 15:37   ` Peter Xu

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