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From:   Peter Xu <peterx@redhat.com>
To:     linux-mm@kvack.org, linux-kernel@vger.kernel.org
Cc:     Gal Pressman <galpress@amazon.com>,
        Matthew Wilcox <willy@infradead.org>,
        Wei Zhang <wzam@amazon.com>, peterx@redhat.com,
        Mike Kravetz <mike.kravetz@oracle.com>,
        Mike Rapoport <rppt@linux.vnet.ibm.com>,
        Christoph Hellwig <hch@lst.de>,
        Andrew Morton <akpm@linux-foundation.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        David Gibson <david@gibson.dropbear.id.au>,
        Jason Gunthorpe <jgg@ziepe.ca>, Jann Horn <jannh@google.com>,
        Kirill Tkhai <ktkhai@virtuozzo.com>,
        Kirill Shutemov <kirill@shutemov.name>,
        Miaohe Lin <linmiaohe@huawei.com>,
        Andrea Arcangeli <aarcange@redhat.com>, Jan Kara <jack@suse.cz>
Subject: [PATCH v5 0/5] mm/hugetlb: Early cow on fork, and a few cleanups
Date:   Wed, 17 Feb 2021 18:35:42 -0500
Message-Id: <20210217233547.93892-1-peterx@redhat.com>
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v5:=0D
- patch 4: change "int cow" into "bool cow"=0D
- collect r-bs for Jason=0D
=0D
v4:=0D
- add r-b for Mike on the last patch, add some more commit message explains=
=0D
  that why we don't need wr-protect trick=0D
- fix one warning of unused var in copy_present_page() [Gal]=0D
=0D
v3:=0D
- rebase to linux-next/akpm, switch to the new HPAGE helpers [MikeK]=0D
- correct error check for alloc_huge_page(); test it this time to make sure=
=0D
  fork() fails gracefully when overcommit [MikeK]=0D
- move page copy out of pgtable lock: this changed quite a bit of the logic=
 in=0D
  the last patch, prealloc is dropped since I found it easier to understand=
=0D
  without looping at all [MikeK]=0D
=0D
v2:=0D
- pass in 1 to alloc_huge_page() last param [Mike]=0D
- reduce comment, unify the comment in one place [Linus]=0D
- add r-bs for Mike and Miaohe=0D
=0D
---- original cover letter ----=0D
=0D
As reported by Gal [1], we still miss the code clip to handle early cow for=
=0D
hugetlb case, which is true.  Again, it still feels odd to fork() after usi=
ng a=0D
few huge pages, especially if they're privately mapped to me..  However I d=
o=0D
agree with Gal and Jason in that we should still have that since that'll=0D
complete the early cow on fork effort at least, and it'll still fix issues=
=0D
where buffers are not well under control and not easy to apply MADV_DONTFOR=
K.=0D
=0D
The first two patches (1-2) are some cleanups I noticed when reading into t=
he=0D
hugetlb reserve map code.  I think it's good to have but they're not necess=
ary=0D
for fixing the fork issue.=0D
=0D
The last two patches (3-4) is the real fix.=0D
=0D
I tested this with a fork() after some vfio-pci assignment, so I'm pretty s=
ure=0D
the page copy path could trigger well (page will be accounted right after t=
he=0D
fork()), but I didn't do data check since the card I assigned is some rando=
m=0D
nic.  Gal, please feel free to try this if you have better way to verify th=
e=0D
series.=0D
=0D
  https://github.com/xzpeter/linux/tree/fork-cow-pin-huge=0D
=0D
Please review, thanks!=0D
=0D
[1] https://lore.kernel.org/lkml/27564187-4a08-f187-5a84-3df50009f6ca@amazo=
n.com/=0D
=0D
Peter Xu (5):=0D
  hugetlb: Dedup the code to add a new file_region=0D
  hugetlg: Break earlier in add_reservation_in_range() when we can=0D
  mm: Introduce page_needs_cow_for_dma() for deciding whether cow=0D
  mm: Use is_cow_mapping() across tree where proper=0D
  hugetlb: Do early cow when page pinned on src mm=0D
=0D
 drivers/gpu/drm/vmwgfx/vmwgfx_page_dirty.c |   4 +-=0D
 drivers/gpu/drm/vmwgfx/vmwgfx_ttm_glue.c   |   2 +-=0D
 fs/proc/task_mmu.c                         |   2 -=0D
 include/linux/mm.h                         |  21 ++++=0D
 mm/huge_memory.c                           |   8 +-=0D
 mm/hugetlb.c                               | 123 +++++++++++++++------=0D
 mm/internal.h                              |   5 -=0D
 mm/memory.c                                |   8 +-=0D
 8 files changed, 117 insertions(+), 56 deletions(-)=0D
=0D
-- =0D
2.26.2=0D
=0D