From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753595AbcEWTCE (ORCPT ); Mon, 23 May 2016 15:02:04 -0400 Received: from mga11.intel.com ([192.55.52.93]:57405 "EHLO mga11.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752074AbcEWTCD (ORCPT ); Mon, 23 May 2016 15:02:03 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.26,356,1459839600"; d="scan'208";a="972912153" Date: Mon, 23 May 2016 22:01:54 +0300 From: "Kirill A. Shutemov" To: Rik van Riel Cc: Michal Hocko , Ebru Akagunduz , linux-mm@kvack.org, hughd@google.com, akpm@linux-foundation.org, n-horiguchi@ah.jp.nec.com, aarcange@redhat.com, iamjoonsoo.kim@lge.com, gorcunov@openvz.org, linux-kernel@vger.kernel.org, mgorman@suse.de, rientjes@google.com, vbabka@suse.cz, aneesh.kumar@linux.vnet.ibm.com, hannes@cmpxchg.org, boaz@plexistor.com Subject: Re: [PATCH 3/3] mm, thp: make swapin readahead under down_read of mmap_sem Message-ID: <20160523190154.GA79357@black.fi.intel.com> References: <1464023651-19420-1-git-send-email-ebru.akagunduz@gmail.com> <1464023651-19420-4-git-send-email-ebru.akagunduz@gmail.com> <20160523184246.GE32715@dhcp22.suse.cz> <1464029349.16365.58.camel@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1464029349.16365.58.camel@redhat.com> User-Agent: Mutt/1.5.23.1 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, May 23, 2016 at 02:49:09PM -0400, Rik van Riel wrote: > On Mon, 2016-05-23 at 20:42 +0200, Michal Hocko wrote: > > On Mon 23-05-16 20:14:11, Ebru Akagunduz wrote: > > > > > > Currently khugepaged makes swapin readahead under > > > down_write. This patch supplies to make swapin > > > readahead under down_read instead of down_write. > > You are still keeping down_write. Can we do without it altogether? > > Blocking mmap_sem of a remote proces for write is certainly not nice. > > Maybe Andrea can explain why khugepaged requires > a down_write of mmap_sem? > > If it were possible to have just down_read that > would make the code a lot simpler. You need a down_write() to retract page table. We need to make sure that nobody sees the page table before we can replace it with huge pmd. -- Kirill A. Shutemov