linux-kernel - Re: [PATCH] mm: don't allow fault_around

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Message-ID: <alpine.DEB.2.02.1407281542460.8998@chino.kir.corp.google.com>
Date:	Mon, 28 Jul 2014 15:43:26 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Andrey Ryabinin <a.ryabinin@...sung.com>
cc:	"Kirill A. Shutemov" <kirill@...temov.name>,
	Sasha Levin <sasha.levin@...cle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andi Kleen <ak@...ux.intel.com>,
	Matthew Wilcox <matthew.r.wilcox@...el.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Dave Chinner <david@...morbit.com>, Ning Qu <quning@...il.com>,
	linux-mm@...ck.org, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, Dave Jones <davej@...hat.com>,
	stable@...r.kernel.org,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Mel Gorman <mgorman@...e.de>, Rik van Riel <riel@...hat.com>,
	Konstantin Khlebnikov <koct9i@...il.com>,
	Hugh Dickins <hughd@...gle.com>
Subject: Re: [PATCH] mm: don't allow fault_around_bytes to be 0

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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