Re: [PATCH 1/8] mm: munlock use follow_page

[Hiroaki Wakabayashi]

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