From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx170.postini.com [74.125.245.170]) by kanga.kvack.org (Postfix) with SMTP id 61A2F6B0071 for ; Sun, 13 Jan 2013 11:09:58 -0500 (EST) Date: Sun, 13 Jan 2013 18:10:57 +0200 From: "Kirill A. Shutemov" Subject: Re: huge zero page vs FOLL_DUMP Message-ID: <20130113161056.GA2046@otc-wbsnb-06> References: <20130112033659.GA26890@otc-wbsnb-06> <1358041388.31895.0.camel@kernel.cn.ibm.com> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="T4sUOijqQbZv57TR" Content-Disposition: inline In-Reply-To: <1358041388.31895.0.camel@kernel.cn.ibm.com> Sender: owner-linux-mm@kvack.org List-ID: To: Simon Jeons Cc: Michel Lespinasse , Hugh Dickins , linux-mm --T4sUOijqQbZv57TR Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Sat, Jan 12, 2013 at 07:43:08PM -0600, Simon Jeons wrote: > On Sat, 2013-01-12 at 05:36 +0200, Kirill A. Shutemov wrote: > > On Fri, Jan 11, 2013 at 03:53:34PM -0800, Michel Lespinasse wrote: > > > Hi, > > >=20 > > > follow_page() has code to return ERR_PTR(-EFAULT) when it encounters > > > the zero page and FOLL_DUMP flag is passed - this is used to avoid > > > dumping the zero page to disk when doing core dumps, and also by > > > munlock to avoid having potentially large number of threads trying to > > > munlock the zero page at once, which we can't reclaim anyway. > > >=20 > > > We don't have the corresponding logic when follow_page() encounters a > > > huge zero page. I think we should, preferably before 3.8. However, I > > > am slightly confused as to what to do for the munlock case, as the > > > huge zero page actually does seem to be reclaimable. My guess is that > > > we could still skip the munlocks, until the zero page is actually > > > reclaimed at which point we should check if we can munlock it. > > >=20 > > > Kirill, is this something you would have time to look into ? > >=20 > > Nice catch! Thank you. > >=20 > > I don't think we should do anything about mlock(). Huge zero page cannot > > be mlocked -- it will not pass page->mapping check in >=20 > Hi Kirill, >=20 > What's store in page->mapping of huge zero page? NULL. --=20 Kirill A. Shutemov --T4sUOijqQbZv57TR Content-Type: application/pgp-signature; name="signature.asc" Content-Description: Digital signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.12 (GNU/Linux) iQIcBAEBAgAGBQJQ8tyQAAoJEAd+omnVudOMncQP/1hTBejcZ96ugWXfzAFC9O1v Rq5ZTpnkYbmCBt+m6NGn6gw0mZDnUpH42EMVAy34RrL4BfOsClkXRB4CP0zaKP+i G3QE10Mj37+mF+VnekZTjuAH7sbygst4Roi7ZzXiKBPuIYMFkSLdYfpkxdSmVQi0 4qOryAV87gXi74bNXr1rYSc/0VADEYaTKsryPXaadlJk/AX+WY29GKqUiCq6CgLG Ey0/y4pK7UsUYgWVW7SoIHoHZwmMFmyiIwZywGTWYFydBA8klZAHG3GyNohEzUGZ HDYE22/wYSeLtvp9AX5JDXB8QL3K/i3jEWTZdQ6SGdKM8DGy26hVZd4kJtT5UTt3 Ofpult4m9xLwYz3448iknJKa+wCz15Z/ZYrP/BOYy/emx1NkcBgQsBrN+UU0MBQM 8yTqDqZGut7hM3qn/ba3b1cL+KSzS1R+OJ+cKG2Ki3RwhTgm7PKbfCZ6dIHJSD/8 XQIGrcRVltUouExhedLYXnCHqrx2RM2zfXh9IKaiMyVnTRcRfVXyQ/MVMAC5ouaU Hk+HQet5k0cBoESr7JhlMSxN3DmO9gftgnYlo0xootuogWXmASq/mkC0XqmGwvWg BaT5Q+yVI88jrs8CabucOHWOGZetaIaq0GdQTDch+jJOdvrWeK+3NBhqWR+pakF4 I4tLJB+pIqjMzsVE2VtN =gvF9 -----END PGP SIGNATURE----- --T4sUOijqQbZv57TR-- -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org