linux-kernel - Re: [PATCH] mm: hugetlb: flush dcache before returning zeroed huge page to userspace

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Message-ID: <20120816173459.GB7203@mudshark.cambridge.arm.com>
Date:	Thu, 16 Aug 2012 18:34:59 +0100
From:	Will Deacon <will.deacon@....com>
To:	Michal Hocko <mhocko@...e.cz>
Cc:	Hugh Dickins <hughd@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Hillf Danton <dhillf@...il.com>,
	Russell King <linux@....linux.org.uk>,
	"linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>
Subject: Re: [PATCH] mm: hugetlb: flush dcache before returning zeroed huge
 page to userspace

On Thu, Aug 16, 2012 at 06:25:27PM +0100, Michal Hocko wrote:
> On Thu 16-08-12 17:09:54, Will Deacon wrote:
> > On Wed, Aug 08, 2012 at 05:26:07PM +0100, Michal Hocko wrote:
> > > I guess the cleanest way is to hook into dequeue_huge_page_node and add
> > > something like arch_clear_hugepage_flags.
> > 
> > I hooked into enqueue_huge_page instead, but how about something like this?:
> 
> Do you have any specific reason for that? enqueue_huge_page is called on
> pages which potentially never get used so isn't that wasting a bit?
> Not that it would be wrong I was just thinking why shouldn't we do it
> when the page is actualy going to be used for sure.

I just did it that way to match the flag clearing for normal pages. I can
move it into dequeue if you think it's worthwhile but in the worst case it
just adds a clear_bit call, so I doubt it's measurable.

Will
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