Re: [PATCH 1/8] mm: munlock use follow_page
From: Hiroaki Wakabayashi
Date: Fri Sep 11 2009 - 07:12:57 EST
2009年9月8日 Hugh Dickins <hugh.dickins@xxxxxxxxxxxxx>:
>
Hiroaki Wakabayashi points out that when mlock() has been interrupted
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by SIGKILL, the subsequent munlock() takes unnecessarily long because
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its use of __get_user_pages() insists on faulting in all the pages
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which mlock() never reached.
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>
It's worse than slowness if mlock() is terminated by Out Of Memory kill:
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the munlock_vma_pages_all() in exit_mmap() insists on faulting in all the
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pages which mlock() could not find memory for; so innocent bystanders are
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killed too, and perhaps the system hangs.
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>
__get_user_pages() does a lot that's silly for munlock(): so remove the
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munlock option from __mlock_vma_pages_range(), and use a simple loop of
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follow_page()s in munlock_vma_pages_range() instead; ignoring absent
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pages, and not marking present pages as accessed or dirty.
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(Change munlock() to only go so far as mlock() reached? That does not
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work out, given the convention that mlock() claims complete success even
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when it has to give up early - in part so that an underlying file can be
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extended later, and those pages locked which earlier would give SIGBUS.)
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>
Signed-off-by: Hugh Dickins <hugh.dickins@xxxxxxxxxxxxx>
Reviewed-by: Hiroaki Wakabayashi <primulaelatior@xxxxxxxxx>
It very simple and so cool! I have learned something.
--
Thanks,
Hiroaki Wakabayashi
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