From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752932AbbC3L7K (ORCPT ); Mon, 30 Mar 2015 07:59:10 -0400 Received: from cantor2.suse.de ([195.135.220.15]:54555 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751806AbbC3L7H (ORCPT ); Mon, 30 Mar 2015 07:59:07 -0400 Date: Mon, 30 Mar 2015 12:59:01 +0100 From: Mel Gorman To: Naoya Horiguchi Cc: Naoya Horiguchi , "linux-mm@kvack.org" , Andrew Morton , Hugh Dickins , "Kirill A. Shutemov" , David Rientjes , Rik van Riel , "linux-kernel@vger.kernel.org" Subject: Re: [RFC][PATCH] mm: hugetlb: add stub-like do_hugetlb_numa() Message-ID: <20150330115901.GR4701@suse.de> References: <1427708426-31610-1-git-send-email-n-horiguchi@ah.jp.nec.com> <20150330102802.GQ4701@suse.de> <55192885.5010608@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline In-Reply-To: <55192885.5010608@gmail.com> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Mar 30, 2015 at 07:42:13PM +0900, Naoya Horiguchi wrote: > On 03/30/2015 07:28 PM, Mel Gorman wrote: > >On Mon, Mar 30, 2015 at 09:40:54AM +0000, Naoya Horiguchi wrote: > >>hugetlb doesn't support NUMA balancing now, but that doesn't mean that we > >>don't have to make hugetlb code prepared for PROTNONE entry properly. > >>In the current kernel, when a process accesses to hugetlb range protected > >>with PROTNONE, it causes unexpected COWs, which finally put hugetlb subsystem > >>into broken/uncontrollable state, where for example h->resv_huge_pages is > >>subtracted too much and wrapped around to a very large number, and free > >>hugepage pool is no longer maintainable. > >> > > > >Ouch! > > > >>This patch simply clears PROTNONE when it's caught out. Real NUMA balancing > >>code for hugetlb is not implemented yet (not sure how much it's worth doing.) > >> > > > >It's not worth doing at all. Furthermore, an application that took the > >effort to allocate and use hugetlb pages is not going to appreciate the > >minor faults incurred by automatic balancing for no gain. > > OK, > > >Why not something > >like the following untested patch? > > I'll test this tomorrow. > Thank you very much for the comment. > I note now that the patch was too hasty. By rights, that check should be covered by vma_migratable() but it's only checked if CONFIG_ARCH_ENABLE_HUGEPAGE_MIGRATION which means it's x86-only. If you are seeing this problem on any other arch then a more correct fix might be to remove the CONFIG_ARCH_ENABLE_HUGEPAGE_MIGRATION check in vma_migratable. -- Mel Gorman SUSE Labs