From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751279AbdCPGbp (ORCPT ); Thu, 16 Mar 2017 02:31:45 -0400 Received: from mga06.intel.com ([134.134.136.31]:61021 "EHLO mga06.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750866AbdCPGbo (ORCPT ); Thu, 16 Mar 2017 02:31:44 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.36,170,1486454400"; d="scan'208";a="1109009911" From: "Huang\, Ying" To: Tim Chen Cc: "Huang\, Ying" , Andrew Morton , , , Andrea Arcangeli , "Kirill A . Shutemov" , Hugh Dickins , Shaohua Li , Minchan Kim , Rik van Riel Subject: Re: [PATCH -mm -v6 3/9] mm, THP, swap: Add swap cluster allocate/free functions References: <20170308072613.17634-1-ying.huang@intel.com> <20170308072613.17634-4-ying.huang@intel.com> <1489533213.2733.33.camel@linux.intel.com> <87wpbrcp5s.fsf@yhuang-dev.intel.com> <1489598142.2733.60.camel@linux.intel.com> Date: Thu, 16 Mar 2017 14:31:40 +0800 In-Reply-To: <1489598142.2733.60.camel@linux.intel.com> (Tim Chen's message of "Wed, 15 Mar 2017 10:15:42 -0700") Message-ID: <87bmt1yboz.fsf@yhuang-dev.intel.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/25.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Tim Chen writes: > On Wed, 2017-03-15 at 09:19 +0800, Huang, Ying wrote: >> Tim Chen writes: >> >> > >> > On Wed, 2017-03-08 at 15:26 +0800, Huang, Ying wrote: >> > > >> > > From: Huang Ying >> > > >> > > The swap cluster allocation/free functions are added based on the >> > > existing swap cluster management mechanism for SSD.  These functions >> > > don't work for the rotating hard disks because the existing swap cluster >> > > management mechanism doesn't work for them.  The hard disks support may >> > > be added if someone really need it.  But that needn't be included in >> > > this patchset. >> > > >> > > This will be used for the THP (Transparent Huge Page) swap support. >> > > Where one swap cluster will hold the contents of each THP swapped out. >> > > >> > > Cc: Andrea Arcangeli >> > > Cc: Kirill A. Shutemov >> > > Cc: Hugh Dickins >> > > Cc: Shaohua Li >> > > Cc: Minchan Kim >> > > Cc: Rik van Riel >> > > Signed-off-by: "Huang, Ying" >> > > --- >> > >  mm/swapfile.c | 217 +++++++++++++++++++++++++++++++++++++++++----------------- >> > >  1 file changed, 156 insertions(+), 61 deletions(-) >> > > >> > > diff --git a/mm/swapfile.c b/mm/swapfile.c >> > > index a744604384ff..91876c33114b 100644 >> > > --- a/mm/swapfile.c >> > > +++ b/mm/swapfile.c >> > > @@ -378,6 +378,14 @@ static void swap_cluster_schedule_discard(struct swap_info_struct *si, >> > >   schedule_work(&si->discard_work); >> > >  } >> > >   >> > > +static void __free_cluster(struct swap_info_struct *si, unsigned long idx) >> > > +{ >> > > + struct swap_cluster_info *ci = si->cluster_info; >> > > + >> > > + cluster_set_flag(ci + idx, CLUSTER_FLAG_FREE); >> > > + cluster_list_add_tail(&si->free_clusters, ci, idx); >> > > +} >> > > + >> > >  /* >> > >   * Doing discard actually. After a cluster discard is finished, the cluster >> > >   * will be added to free cluster list. caller should hold si->lock. >> > > @@ -398,10 +406,7 @@ static void swap_do_scheduled_discard(struct swap_info_struct *si) >> > >   >> > >   spin_lock(&si->lock); >> > >   ci = lock_cluster(si, idx * SWAPFILE_CLUSTER); >> > > - cluster_set_flag(ci, CLUSTER_FLAG_FREE); >> > > - unlock_cluster(ci); >> > > - cluster_list_add_tail(&si->free_clusters, info, idx); >> > > - ci = lock_cluster(si, idx * SWAPFILE_CLUSTER); >> > > + __free_cluster(si, idx); >> > >   memset(si->swap_map + idx * SWAPFILE_CLUSTER, >> > >   0, SWAPFILE_CLUSTER); >> > >   unlock_cluster(ci); >> > The __free_cluster definition and the above change to eliminate >> > the extra unlock_cluster and lock_cluster can perhaps be broken up >> > as a separate patch.  It can be independent of THP changes. >> I think the change may have no value by itself without THP changes. >> There will be only 1 user of __free_cluster() and the lock change is >> trivial too.  So I think it may be better just to keep it as that? >> > > Seems like the extra unlock and lock of cluster in existing code should be taken out > irrespective of the THP changes: >   > cluster_set_flag(ci, CLUSTER_FLAG_FREE); > - unlock_cluster(ci); > cluster_list_add_tail(&si->free_clusters, info, idx); > - ci = lock_cluster(si, idx * SWAPFILE_CLUSTER); > memset(si->swap_map + idx * SWAPFILE_CLUSTER, >    0, SWAPFILE_CLUSTER); > This is not a functionality fix or performance optimization. Because the lock on the swap_info_struct is held during the operation and there are no operations on cluster with index "idx" in cluster_list_add_tail(). The change here is just to make the resulting code a little simpler. Is this deserved a separate patch? Best Regards, Huang, Ying