linux-kernel - Re: [PATCH 5/8] mm: make clear_huge_page cache clear only around the fault address

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Message-ID: <520E6951.2040909@intel.com>
Date:	Fri, 16 Aug 2013 11:02:57 -0700
From:	Dave Hansen <dave.hansen@...el.com>
To:	Alex Thorlton <athorlton@....com>
CC:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mgorman@...e.de>,
	"Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
	Rik van Riel <riel@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	"Eric W . Biederman" <ebiederm@...ssion.com>,
	Sedat Dilek <sedat.dilek@...il.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Dave Jones <davej@...hat.com>,
	Michael Kerrisk <mtk.manpages@...il.com>,
	"Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>,
	David Howells <dhowells@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Al Viro <viro@...iv.linux.org.uk>,
	Oleg Nesterov <oleg@...hat.com>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Kees Cook <keescook@...omium.org>, Robin Holt <holt@....com>
Subject: Re: [PATCH 5/8] mm: make clear_huge_page cache clear only around
 the fault address

On 08/16/2013 07:34 AM, Alex Thorlton wrote:
> +#if ARCH_HAS_USER_NOCACHE == 0
> +#define clear_user_highpage_nocache clear_user_highpage
> +#endif
...
>  		cond_resched();
> -		clear_user_highpage(p, addr + i * PAGE_SIZE);
> +		vaddr = haddr + i*PAGE_SIZE;
> +		if (!ARCH_HAS_USER_NOCACHE  || i == target)
> +			clear_user_highpage(p, vaddr);
> +		else
> +			clear_user_highpage_nocache(p, vaddr);
>  	}
>  }

Is the check for !ARCH_HAS_USER_NOCACHE in there really necessary?  That
logic seems like it would be taken care of by that #define.

Plus, if you don't check 'ARCH_HAS_USER_NOCACHE' like this, you don't
need to define a value for it, and you can axe the:

+#ifndef ARCH_HAS_USER_NOCACHE
+#define ARCH_HAS_USER_NOCACHE 0
+#endif
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