From: Andrea Arcangeli <aarcange@redhat.com>
To: "Kirill A. Shutemov" <kirill@shutemov.name>
Cc: Dan Williams <dan.j.williams@intel.com>, linux-mm@kvack.org
Subject: Re: THP race?
Date: Tue, 23 Feb 2016 20:28:35 +0100 [thread overview]
Message-ID: <20160223192835.GJ9157@redhat.com> (raw)
In-Reply-To: <20160223183832.GB21820@node.shutemov.name>
On Tue, Feb 23, 2016 at 09:38:32PM +0300, Kirill A. Shutemov wrote:
> pmd_trans_unstable(pmd), otherwise looks good:
Yes sorry.
> Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Thanks for the quick ack, I just noticed or I would have added it to
the resubmit, but it can be still added to -mm.
> BTW, I guess DAX would need to introduce the same infrastructure for
> pmd_devmap(). Dan?
There is a i_mmap_lock_write in the truncate path that saves the day
for the pmd zapping in the truncate() case without mmap_sem (the only
case anon THP doesn't need to care about as truncate isn't possible in
the anon case), but not in the MADV_DONTNEED madvise case that runs
only with the mmap_sem for reading.
The only objective of this "infrastructure" is to add no pmd_lock()ing
overhead to the page fault, if the mapping is already established but
not huge, and we've just to walk through the pmd to reach the
pte. All because MADV_DONTNEED is running with the mmap_sem for
reading unlike munmap and other slower syscalls that are forced to
mangle the vmas and have to take the mmap_sem for writing regardless.
The question for DAX is if it should do a pmd_devmap check inside
pmd_none_or_trans_huge_or_clear_bad() after pmd_trans_huge() and get
away with a one liner, or add its own infrastructure with
pmd_devmap_unstable(). In the pmd_devmap case the problem isn't just
in __handle_mm_fault. If it could share the same infrastructure it'd
be ideal.
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next prev parent reply other threads:[~2016-02-23 19:28 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-02-23 15:49 THP race? Kirill A. Shutemov
2016-02-23 18:06 ` Andrea Arcangeli
2016-02-23 18:18 ` [PATCH 1/1] mm: thp: fix SMP race condition between THP page fault kbuild test robot
2016-02-23 18:21 ` kbuild test robot
2016-02-23 18:27 ` kbuild test robot
2016-02-23 18:38 ` THP race? Kirill A. Shutemov
2016-02-23 19:28 ` Andrea Arcangeli [this message]
2016-02-25 18:45 ` Dan Williams
2016-02-26 10:37 ` Kirill A. Shutemov
2016-02-26 14:46 ` Dan Williams
2016-02-23 18:49 ` [PATCH 0/1] " Andrea Arcangeli
2016-02-23 18:49 ` [PATCH 1/1] mm: thp: fix SMP race condition between THP page fault and MADV_DONTNEED Andrea Arcangeli
2016-02-23 21:18 ` Andrew Morton
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