linux-kernel - Re: [PATCH] proc: pagemap: Hold mmap

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Date:	Thu,  1 Apr 2010 11:10:01 +0900 (JST)
From:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	kosaki.motohiro@...fujitsu.com, Matt Mackall <mpm@...enic.com>,
	San Mehat <san@...gle.com>, linux-kernel@...r.kernel.org,
	Brian Swetland <swetland@...gle.com>,
	Dave Hansen <haveblue@...ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] proc: pagemap: Hold mmap_sem during page walk

> So there is a very real reason for that pattern existing. It's just that 
> that reason has nothing to do with locking the thing into the page tables. 
> That is absolutely NOT guaranteed by the get_user_pages() physical page 
> pinning (munmap() is an extreme example of this, but I think swapout will 
> clear it too in try_to_unmap_one().

Right. To increment page->count only affect vmscan to prevent free page.
Not prevent pageout I/O nor page unmapping from a process.

Thanks.


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