linux-kernel - Re: [PATCH 0/5] fix up /proc/$pid/smaps to not split huge pages

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Message-ID: <20110215170152.GF5935@random.random>
Date:	Tue, 15 Feb 2011 18:01:52 +0100
From:	Andrea Arcangeli <aarcange@...hat.com>
To:	Eric B Munson <emunson@...bm.net>
Cc:	Dave Hansen <dave@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Michael J Wolf <mjwolf@...ibm.com>
Subject: Re: [PATCH 0/5] fix up /proc/$pid/smaps to not split huge pages

On Tue, Feb 15, 2011 at 11:55:10AM -0500, Eric B Munson wrote:
> I am noticing in smaps that KernelPageSize is wrong of areas
> that have been merged into THP.  For instance:
> 
> 7ff852a00000-7ff852c00000 rw-p 00000000 00:00 0 
> Size:               2048 kB
> Rss:                2048 kB
> Pss:                2048 kB
> Shared_Clean:          0 kB
> Shared_Dirty:          0 kB
> Private_Clean:         0 kB
> Private_Dirty:      2048 kB
> Referenced:         2048 kB
> Anonymous:          2048 kB
> AnonHugePages:      2048 kB
> Swap:                  0 kB
> KernelPageSize:        4 kB
> MMUPageSize:           4 kB
> Locked:                0 kB
> 
> The entire mapping is contained in a THP but the
> KernelPageSize shows 4kb.  For cases where the mapping might
> have mixed page sizes this may be okay, but for this
> particular mapping the 4kb page size is wrong.

I'm not sure this is a bug, if the mapping grows it may become 4096k
but the new pages may be 4k. There's no such thing as a
vma_mmu_pagesize in terms of hugepages because we support graceful
fallback and collapse/split on the fly without altering the vma. So I
think 4k is correct here.

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