From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752633AbbFRAem (ORCPT ); Wed, 17 Jun 2015 20:34:42 -0400 Received: from mail-ig0-f170.google.com ([209.85.213.170]:34423 "EHLO mail-ig0-f170.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751868AbbFRAee (ORCPT ); Wed, 17 Jun 2015 20:34:34 -0400 Date: Wed, 17 Jun 2015 17:34:31 -0700 (PDT) From: David Rientjes X-X-Sender: rientjes@chino.kir.corp.google.com To: Vlastimil Babka cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, Andrew Morton , Hugh Dickins , Andrea Arcangeli , "Kirill A. Shutemov" , Rik van Riel , Mel Gorman , Michal Hocko , Alex Thorlton Subject: Re: [RFC 1/4] mm, thp: stop preallocating hugepages in khugepaged In-Reply-To: <1431354940-30740-2-git-send-email-vbabka@suse.cz> Message-ID: References: <1431354940-30740-1-git-send-email-vbabka@suse.cz> <1431354940-30740-2-git-send-email-vbabka@suse.cz> User-Agent: Alpine 2.10 (DEB 1266 2009-07-14) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 11 May 2015, Vlastimil Babka wrote: > Khugepaged tries to preallocate a hugepage before scanning for THP collapse > candidates. If the preallocation fails, scanning is not attempted. This makes > sense, but it is only restricted to !NUMA configurations, where it does not > need to predict on which node to preallocate. > > Besides the !NUMA restriction, the preallocated page may also end up being > unused and put back when no collapse candidate is found. I have observed the > thp_collapse_alloc vmstat counter to have 3+ times the value of the counter > of actually collapsed pages in /sys/.../khugepaged/pages_collapsed. On the > other hand, the periodic hugepage allocation attempts involving sync > compaction can be beneficial for the antifragmentation mechanism, but that's > however harder to evaluate. > > The following patch will introduce per-node THP availability tracking, which > has more benefits than current preallocation and is applicable to CONFIG_NUMA. > We can therefore remove the preallocation, which also allows a cleanup of the > functions involved in khugepaged allocations. Another small benefit of the > patch is that NUMA configs can now reuse an allocated hugepage for another > collapse attempt, if the previous one was for the same node and failed. > > Signed-off-by: Vlastimil Babka I think this is fine if the rest of the series is adopted, and I understand how the removal and cleanup is easier when done first before the following patches. I think you can unify alloc_hugepage_node() for both NUMA and !NUMA configs and inline it in khugepaged_alloc_page().