Date: Thu, 15 Nov 2012 11:41:55 +0200
From: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
To: David Rientjes <rientjes@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
        Andrea Arcangeli <aarcange@redhat.com>, linux-mm@kvack.org,
        Andi Kleen <ak@linux.intel.com>,
        "H. Peter Anvin" <hpa@linux.intel.com>, linux-kernel@vger.kernel.org,
        "Kirill A. Shutemov" <kirill@shutemov.name>
Subject: Re: [PATCH v5 09/11] thp: lazy huge zero page allocation
Message-ID: <20121115094155.GG9676@otc-wbsnb-06>
References: <1352300463-12627-1-git-send-email-kirill.shutemov@linux.intel.com>
 <1352300463-12627-10-git-send-email-kirill.shutemov@linux.intel.com>
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On Wed, Nov 14, 2012 at 03:37:09PM -0800, David Rientjes wrote:
> On Wed, 7 Nov 2012, Kirill A. Shutemov wrote:
>=20
> > From: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
> >=20
> > Instead of allocating huge zero page on hugepage_init() we can postpone=
 it
> > until first huge zero page map. It saves memory if THP is not in use.
> >=20
>=20
> Is it worth the branch on every non-write pagefault after that?  The=20
> unlikely() is not going to help on x86.  If thp is enabled in your=20
> .config (which isn't the default), then I think it's better to just=20
> allocate the zero huge page once and avoid any branches after that to=20
> lazily allocate it.  (Or do it only when thp is set to "madvise" or=20
> "always" if booting with transparent_hugepage=3Dnever.)

I can rewrite the check to static_key if you want. Would it be better?

--=20
 Kirill A. Shutemov

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