From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 7E1DCCA9ECE for ; Thu, 31 Oct 2019 20:50:57 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 5BF962086D for ; Thu, 31 Oct 2019 20:50:57 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727647AbfJaUu4 (ORCPT ); Thu, 31 Oct 2019 16:50:56 -0400 Received: from mail105.syd.optusnet.com.au ([211.29.132.249]:34322 "EHLO mail105.syd.optusnet.com.au" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727511AbfJaUu4 (ORCPT ); Thu, 31 Oct 2019 16:50:56 -0400 Received: from dread.disaster.area (pa49-180-67-183.pa.nsw.optusnet.com.au [49.180.67.183]) by mail105.syd.optusnet.com.au (Postfix) with ESMTPS id EBB5A3A27CA; Fri, 1 Nov 2019 07:50:51 +1100 (AEDT) Received: from dave by dread.disaster.area with local (Exim 4.92.3) (envelope-from ) id 1iQHP7-00067n-Az; Fri, 01 Nov 2019 07:50:49 +1100 Date: Fri, 1 Nov 2019 07:50:49 +1100 From: Dave Chinner To: "Darrick J. Wong" Cc: linux-xfs@vger.kernel.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org Subject: Re: [PATCH 04/26] xfs: Improve metadata buffer reclaim accountability Message-ID: <20191031205049.GS4614@dread.disaster.area> References: <20191009032124.10541-1-david@fromorbit.com> <20191009032124.10541-5-david@fromorbit.com> <20191030172517.GO15222@magnolia> <20191030214335.GQ4614@dread.disaster.area> <20191031030658.GW15222@magnolia> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20191031030658.GW15222@magnolia> User-Agent: Mutt/1.10.1 (2018-07-13) X-Optus-CM-Score: 0 X-Optus-CM-Analysis: v=2.2 cv=P6RKvmIu c=1 sm=1 tr=0 a=3wLbm4YUAFX2xaPZIabsgw==:117 a=3wLbm4YUAFX2xaPZIabsgw==:17 a=jpOVt7BSZ2e4Z31A5e1TngXxSK0=:19 a=kj9zAlcOel0A:10 a=MeAgGD-zjQ4A:10 a=20KFwNOVAAAA:8 a=7-415B0cAAAA:8 a=fPFIRJHpAtQw70PwBpUA:9 a=CjuIK1q_8ugA:10 a=biEYGPWJfzWAr4FL6Ov7:22 Sender: linux-xfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-xfs@vger.kernel.org On Wed, Oct 30, 2019 at 08:06:58PM -0700, Darrick J. Wong wrote: > On Thu, Oct 31, 2019 at 08:43:35AM +1100, Dave Chinner wrote: > > On Wed, Oct 30, 2019 at 10:25:17AM -0700, Darrick J. Wong wrote: > > > On Wed, Oct 09, 2019 at 02:21:02PM +1100, Dave Chinner wrote: > > > > From: Dave Chinner > > > > > > > > The buffer cache shrinker frees more than just the xfs_buf slab > > > > objects - it also frees the pages attached to the buffers. Make sure > > > > the memory reclaim code accounts for this memory being freed > > > > correctly, similar to how the inode shrinker accounts for pages > > > > freed from the page cache due to mapping invalidation. > > > > > > > > We also need to make sure that the mm subsystem knows these are > > > > reclaimable objects. We provide the memory reclaim subsystem with a > > > > a shrinker to reclaim xfs_bufs, so we should really mark the slab > > > > that way. > > > > > > > > We also have a lot of xfs_bufs in a busy system, spread them around > > > > like we do inodes. > > > > > > > > Signed-off-by: Dave Chinner > > > > --- > > > > fs/xfs/xfs_buf.c | 6 +++++- > > > > 1 file changed, 5 insertions(+), 1 deletion(-) > > > > > > > > diff --git a/fs/xfs/xfs_buf.c b/fs/xfs/xfs_buf.c > > > > index e484f6bead53..45b470f55ad7 100644 > > > > --- a/fs/xfs/xfs_buf.c > > > > +++ b/fs/xfs/xfs_buf.c > > > > @@ -324,6 +324,9 @@ xfs_buf_free( > > > > > > > > __free_page(page); > > > > } > > > > + if (current->reclaim_state) > > > > + current->reclaim_state->reclaimed_slab += > > > > + bp->b_page_count; > > > > > > Hmm, ok, I see how ZONE_RECLAIM and reclaimed_slab fit together. > > > > > > > } else if (bp->b_flags & _XBF_KMEM) > > > > kmem_free(bp->b_addr); > > > > _xfs_buf_free_pages(bp); > > > > @@ -2064,7 +2067,8 @@ int __init > > > > xfs_buf_init(void) > > > > { > > > > xfs_buf_zone = kmem_zone_init_flags(sizeof(xfs_buf_t), "xfs_buf", > > > > - KM_ZONE_HWALIGN, NULL); > > > > + KM_ZONE_HWALIGN | KM_ZONE_SPREAD | KM_ZONE_RECLAIM, > > > > > > I guess I'm fine with ZONE_SPREAD too, insofar as it only seems to apply > > > to a particular "use another node" memory policy when slab is in use. > > > Was that your intent? > > > > It's more documentation than anything - that we shouldn't be piling > > these structures all on to one node because that can have severe > > issues with NUMA memory reclaim algorithms. i.e. the xfs-buf > > shrinker sets SHRINKER_NUMA_AWARE, so memory pressure on a single > > node can reclaim all the xfs-bufs on that node without touching any > > other node. > > > > That means, for example, if we instantiate all the AG header buffers > > on a single node (e.g. like we do at mount time) then memory > > pressure on that one node will generate IO stalls across the entire > > filesystem as other nodes doing work have to repopulate the buffer > > cache for any allocation for freeing of space/inodes.. > > > > IOWs, for large NUMA systems using cpusets this cache should be > > spread around all of memory, especially as it has NUMA aware > > reclaim. For everyone else, it's just documentation that improper > > cgroup or NUMA memory policy could cause you all sorts of problems > > with this cache. > > > > It's worth noting that SLAB_MEM_SPREAD is used almost exclusively in > > filesystems for inode caches largely because, at the time (~2006), > > the only reclaimable cache that could grow to any size large enough > > to cause problems was the inode cache. It's been cargo-culted ever > > since, whether it is needed or not (e.g. ceph). > > > > In the case of the xfs_bufs, I've been running workloads recently > > that cache several million xfs_bufs and only a handful of inodes > > rather than the other way around. If we spread inodes because > > caching millions on a single node can cause problems on large NUMA > > machines, then we also need to spread xfs_bufs... > > Hmm, could we capture this as a comment somewhere? Sure, but where? We're planning on getting rid of the KM_ZONE flags in the near future, and most of this is specific to the impacts on XFS. I could put it in xfs-super.c above where we initialise all the slabs, I guess. Probably a separate patch, though.... Cheers, Dave. -- Dave Chinner david@fromorbit.com