From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pl1-f200.google.com (mail-pl1-f200.google.com [209.85.214.200]) by kanga.kvack.org (Postfix) with ESMTP id 569716B0003 for ; Wed, 24 Oct 2018 18:18:58 -0400 (EDT) Received: by mail-pl1-f200.google.com with SMTP id t10-v6so3950996plh.14 for ; Wed, 24 Oct 2018 15:18:58 -0700 (PDT) Received: from mail.linuxfoundation.org (mail.linuxfoundation.org. [140.211.169.12]) by mx.google.com with ESMTPS id n2-v6si5885069plk.255.2018.10.24.15.18.56 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 24 Oct 2018 15:18:57 -0700 (PDT) Date: Wed, 24 Oct 2018 15:18:53 -0700 From: Andrew Morton Subject: Re: [RFC PATCH] mm: don't reclaim inodes with many attached pages Message-Id: <20181024151853.3edd9097400b0d52edff1f16@linux-foundation.org> In-Reply-To: <20181023164302.20436-1-guro@fb.com> References: <20181023164302.20436-1-guro@fb.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Roman Gushchin Cc: "linux-mm@kvack.org" , "linux-kernel@vger.kernel.org" , Kernel Team , Michal Hocko , Rik van Riel , Randy Dunlap On Tue, 23 Oct 2018 16:43:29 +0000 Roman Gushchin wrote: > Spock reported that the commit 172b06c32b94 ("mm: slowly shrink slabs > with a relatively small number of objects") leads to a regression on > his setup: periodically the majority of the pagecache is evicted > without an obvious reason, while before the change the amount of free > memory was balancing around the watermark. > > The reason behind is that the mentioned above change created some > minimal background pressure on the inode cache. The problem is that > if an inode is considered to be reclaimed, all belonging pagecache > page are stripped, no matter how many of them are there. So, if a huge > multi-gigabyte file is cached in the memory, and the goal is to > reclaim only few slab objects (unused inodes), we still can eventually > evict all gigabytes of the pagecache at once. > > The workload described by Spock has few large non-mapped files in the > pagecache, so it's especially noticeable. > > To solve the problem let's postpone the reclaim of inodes, which have > more than 1 attached page. Let's wait until the pagecache pages will > be evicted naturally by scanning the corresponding LRU lists, and only > then reclaim the inode structure. > > ... > > --- a/fs/inode.c > +++ b/fs/inode.c > @@ -730,8 +730,11 @@ static enum lru_status inode_lru_isolate(struct list_head *item, > return LRU_REMOVED; > } > > - /* recently referenced inodes get one more pass */ > - if (inode->i_state & I_REFERENCED) { > + /* > + * Recently referenced inodes and inodes with many attached pages > + * get one more pass. > + */ > + if (inode->i_state & I_REFERENCED || inode->i_data.nrpages > 1) { > inode->i_state &= ~I_REFERENCED; > spin_unlock(&inode->i_lock); > return LRU_ROTATE; hm, why "1"? I guess one could argue that this will encompass long symlinks, but I just made that up to make "1" appear more justifiable ;)