Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752041AbdFLIKB (ORCPT ); Mon, 12 Jun 2017 04:10:01 -0400 Received: from mx2.suse.de ([195.135.220.15]:57630 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751779AbdFLIKA (ORCPT ); Mon, 12 Jun 2017 04:10:00 -0400 Date: Mon, 12 Jun 2017 10:09:57 +0200 From: Jan Kara To: Johannes Weiner Cc: Jan Kara , Jan Kara , "Theodore Ts'o" , Alexander Viro , linux-ext4@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-team@fb.com Subject: Re: [RFC PATCH] fs: ext4: don't trap kswapd and allocating tasks on ext4 inode IO Message-ID: <20170612080957.GA22728@quack2.suse.cz> References: <20170515154634.19733-1-hannes@cmpxchg.org> <20170516143645.GA7316@quack2.suse.cz> <20170516154105.GA22633@cmpxchg.org> <20170516160337.GD7316@quack2.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20170516160337.GD7316@quack2.suse.cz> User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5891 Lines: 129 On Tue 16-05-17 18:03:37, Jan Kara wrote: > On Tue 16-05-17 11:41:05, Johannes Weiner wrote: > > On Tue, May 16, 2017 at 04:36:45PM +0200, Jan Kara wrote: > > > On Mon 15-05-17 11:46:34, Johannes Weiner wrote: > > > > We have observed across several workloads situations where kswapd and > > > > direct reclaimers get stuck in the inode shrinker of the ext4 / mount, > > > > causing allocation latencies across tasks in the system, while there > > > > are dozens of gigabytes of clean page cache covering multiple disks. > > > > > > > > The stack traces of such an instance looks like this: > > > > > > > > [] jbd2_log_wait_commit+0x95/0x110 > > > > [] jbd2_complete_transaction+0x59/0x90 > > > > [] ext4_evict_inode+0x2da/0x480 > > > > [] evict+0xc0/0x190 > > > > [] dispose_list+0x39/0x50 > > > > [] prune_icache_sb+0x4b/0x60 > > > > [] super_cache_scan+0x141/0x190 > > > > [] shrink_slab+0x235/0x440 > > > > [] shrink_zone+0x268/0x2d0 > > > > [] do_try_to_free_pages+0x164/0x410 > > > > [] try_to_free_pages+0xb5/0x160 > > > > [] __alloc_pages_nodemask+0x636/0xb30 > > > > [] alloc_pages_current+0x88/0x120 > > > > [] skb_page_frag_refill+0xc6/0xf0 > > > > [] sk_page_frag_refill+0x1d/0x80 > > > > [] tcp_sendmsg+0x28b/0xb10 > > > > [] inet_sendmsg+0x67/0xa0 > > > > [] sock_sendmsg+0x38/0x50 > > > > [] sock_write_iter+0x78/0xd0 > > > > [] do_iter_readv_writev+0x5e/0xa0 > > > > [] do_readv_writev+0x178/0x210 > > > > [] vfs_writev+0x3c/0x50 > > > > [] do_writev+0x52/0xd0 > > > > [] SyS_writev+0x10/0x20 > > > > [] do_syscall_64+0x50/0xa0 > > > > [] return_from_SYSCALL_64+0x0/0x6a > > > > [] 0xffffffffffffffff > > > > > > > > The inode shrinker has provisions to skip any inodes that require > > > > writeback, to avoid tarpitting the entire system behind a single > > > > object when there are many other pools to recycle memory from. But > > > > that logic doesn't cover the situation where an ext4 inode is clean > > > > but journaled and tied to a commit that yet needs to hit the platter. > > > > > > > > Add a superblock operation that lets the generic inode shrinker query > > > > the filesystem whether evicting a given inode will require any IO; add > > > > an ext4 implementation that checks whether the journal is caught up to > > > > the commit id associated with the inode. > > > > > > > > Fixes: 2d859db3e4a8 ("ext4: fix data corruption in inodes with journalled data") > > > > Signed-off-by: Johannes Weiner > > > > > > OK. I have to say I'm somewhat surprised you use data journalling on some > > > of your files / filesystems but whatever - maybe these are long symlink > > > after all which would make sense. > > > > The filesystem is actually mounted data=ordered and we didn't catch > > anyone in userspace enabling journaling on individual inodes. So we > > assumed this must be from symlinks. > > OK. > > > > And I'm actually doubly surprised you can see these stack traces as > > > these days inode_lru_isolate() checks inode->i_data.nrpages and > > > uncommitted pages cannot be evicted from pagecache > > > (ext4_releasepage() will refuse to free them) so I don't see how > > > such inode can get to dispose_list(). But maybe the inode doesn't > > > really have any pages and i_datasync_tid just happens to be set to > > > the current transaction because it is initialized that way and we > > > are evicting inode that was recently read from disk. > > > > Hm, we're running 4.6, but that already has the nrpages check in > > inode_lru_isolate(). There couldn't be any pages in those inodes by > > the time the shrinker gets to them. > > > > > Anyway if you add: "&& inode->i_data.nrpages" to the test in > > > ext4_evict_inode() do the stalls go away? > > > > Want me to still test this? > > Can you try attached patch? I'd like to confirm the theory before merging > this... Thanks! Ping? Any result with this patch? Honza > From e87281dee65589e07b9251ad98191c1e6c488870 Mon Sep 17 00:00:00 2001 > From: Jan Kara > Date: Tue, 16 May 2017 17:56:36 +0200 > Subject: [PATCH] ext4: Avoid unnecessary stalls in ext4_evict_inode() > > These days inode reclaim calls evict_inode() only when it has no pages > in the mapping. In that case it is not necessary to wait for transaction > commit in ext4_evict_inode() as there can be no pages waiting to be > committed. So avoid unnecessary transaction waiting in that case. > > We still have to keep the check for the case where ext4_evict_inode() > gets called from other paths (e.g. umount) where inode still can have > some page cache pages. > > Reported-by: Johannes Weiner > Signed-off-by: Jan Kara > --- > fs/ext4/inode.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c > index 5834c4d76be8..3aef67ca18ac 100644 > --- a/fs/ext4/inode.c > +++ b/fs/ext4/inode.c > @@ -213,7 +213,8 @@ void ext4_evict_inode(struct inode *inode) > */ > if (inode->i_ino != EXT4_JOURNAL_INO && > ext4_should_journal_data(inode) && > - (S_ISLNK(inode->i_mode) || S_ISREG(inode->i_mode))) { > + (S_ISLNK(inode->i_mode) || S_ISREG(inode->i_mode)) && > + inode->i_data.nrpages) { > journal_t *journal = EXT4_SB(inode->i_sb)->s_journal; > tid_t commit_tid = EXT4_I(inode)->i_datasync_tid; > > -- > 2.12.0 > -- Jan Kara SUSE Labs, CR