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Date: Mon, 28 Jul 2014 15:43:26 -0700 (PDT)
From: David Rientjes <rientjes@google.com>
Subject: Re: [PATCH] mm: don't allow fault_around_bytes to be 0
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References: <53D07E96.5000006@oracle.com> <1406533400-6361-1-git-send-email-a.ryabinin@samsung.com> <20140728093611.GA3975@node.dhcp.inet.fi> <53D62599.6000605@samsung.com>
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To: Andrey Ryabinin <a.ryabinin@samsung.com>
Cc: "Kirill A. Shutemov" <kirill@shutemov.name>, Sasha Levin <sasha.levin@oracle.com>, Andrew Morton <akpm@linux-foundation.org>, Linus Torvalds <torvalds@linux-foundation.org>, Andi Kleen <ak@linux.intel.com>, Matthew Wilcox <matthew.r.wilcox@intel.com>, Dave Hansen <dave.hansen@linux.intel.com>, Alexander Viro <viro@zeniv.linux.org.uk>, Dave Chinner <david@fromorbit.com>, Ning Qu <quning@gmail.com>, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, Dave Jones <davej@redhat.com>, stable@vger.kernel.org, "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>, Mel Gorman <mgorman@suse.de>, Rik van Riel <riel@redhat.com>, Konstantin Khlebnikov <koct9i@gmail.com>, Hugh Dickins <hughd@google.com>

On Mon, 28 Jul 2014, Andrey Ryabinin wrote:

> do_fault_around expects fault_around_bytes rounded down to nearest
> page order. Instead of calling rounddown_pow_of_two every time
> in fault_around_pages()/fault_around_mask() we could do round down
> when user changes fault_around_bytes via debugfs interface.
> 

If you're going to optimize this, it seems like fault_around_bytes would 
benefit from being __read_mostly.

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