From: Jan Kara <jack@suse.cz>
To: Fengguang Wu <fengguang.wu@intel.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
Greg Thelen <gthelen@google.com>, Jan Kara <jack@suse.cz>,
Ying Han <yinghan@google.com>,
"hannes@cmpxchg.org" <hannes@cmpxchg.org>,
KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>,
Rik van Riel <riel@redhat.com>, Mel Gorman <mgorman@suse.de>,
Minchan Kim <minchan.kim@gmail.com>,
Linux Memory Management List <linux-mm@kvack.org>,
LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 5/9] writeback: introduce the pageout work
Date: Thu, 1 Mar 2012 17:38:37 +0100 [thread overview]
Message-ID: <20120301163837.GA13104@quack.suse.cz> (raw)
In-Reply-To: <20120301123640.GA30369@localhost>
On Thu 01-03-12 20:36:40, Wu Fengguang wrote:
> > Please have a think about all of this and see if you can demonstrate
> > how the iput() here is guaranteed safe.
>
> There are already several __iget()/iput() calls inside fs-writeback.c.
> The existing iput() calls already demonstrate its safety?
>
> Basically the flusher works in this way
>
> - the dirty inode list i_wb_list does not reference count the inode at all
>
> - the flusher thread does something analog to igrab() and set I_SYNC
> before going off to writeout the inode
>
> - evict() will wait for completion of I_SYNC
Yes, you are right that currently writeback code already holds inode
references and so it can happen that flusher thread drops the last inode
reference. But currently that could create problems only if someone waits
for flusher thread to make progress while effectively blocking e.g.
truncate from happening. Currently flusher thread handles sync(2) and
background writeback and filesystems take care to not hold any locks
blocking IO / truncate while possibly waiting for these.
But with your addition situation changes significantly - now anyone doing
allocation can block and do allocation from all sorts of places including
ones where we hold locks blocking other fs activity. The good news is that
we use GFP_NOFS in such places. So if GFP_NOFS allocation cannot possibly
depend on a completion of some writeback work, then I'd still be
comfortable with dropping inode references from writeback code. But Andrew
is right this at least needs some arguing...
Honza
--
Jan Kara <jack@suse.cz>
SUSE Labs, CR
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next prev parent reply other threads:[~2012-03-01 16:38 UTC|newest]
Thread overview: 58+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-02-28 14:00 [PATCH 0/9] [RFC] pageout work and dirty reclaim throttling Fengguang Wu
2012-02-28 14:00 ` [PATCH 1/9] memcg: add page_cgroup flags for dirty page tracking Fengguang Wu
2012-02-29 0:50 ` KAMEZAWA Hiroyuki
2012-03-04 1:29 ` Fengguang Wu
2012-02-28 14:00 ` [PATCH 2/9] memcg: add dirty page accounting infrastructure Fengguang Wu
2012-02-28 22:37 ` Andrew Morton
2012-02-29 0:27 ` Fengguang Wu
2012-02-28 14:00 ` [PATCH 3/9] memcg: add kernel calls for memcg dirty page stats Fengguang Wu
2012-02-29 1:10 ` KAMEZAWA Hiroyuki
2012-02-28 14:00 ` [PATCH 4/9] memcg: dirty page accounting support routines Fengguang Wu
2012-02-28 15:15 ` Fengguang Wu
2012-02-28 22:45 ` Andrew Morton
2012-02-29 1:15 ` KAMEZAWA Hiroyuki
2012-02-28 14:00 ` [PATCH 5/9] writeback: introduce the pageout work Fengguang Wu
2012-02-29 0:04 ` Andrew Morton
2012-02-29 2:31 ` Fengguang Wu
2012-02-29 13:28 ` Fengguang Wu
2012-03-01 11:04 ` Jan Kara
2012-03-01 11:41 ` Fengguang Wu
2012-03-01 16:50 ` Jan Kara
2012-03-01 19:46 ` Andrew Morton
2012-03-03 13:25 ` Fengguang Wu
2012-03-07 0:37 ` Andrew Morton
2012-03-07 5:40 ` Fengguang Wu
2012-03-01 19:42 ` Andrew Morton
2012-03-01 21:15 ` Jan Kara
2012-03-01 21:22 ` Andrew Morton
2012-03-01 12:36 ` Fengguang Wu
2012-03-01 16:38 ` Jan Kara [this message]
2012-03-02 4:48 ` Fengguang Wu
2012-03-02 9:59 ` Jan Kara
2012-03-02 10:39 ` Fengguang Wu
2012-03-02 19:57 ` Andrew Morton
2012-03-03 13:55 ` Fengguang Wu
2012-03-03 14:27 ` Fengguang Wu
2012-03-04 11:13 ` Fengguang Wu
2012-03-07 15:48 ` Artem Bityutskiy
2012-03-09 7:31 ` Fengguang Wu
2012-03-09 9:51 ` Jan Kara
2012-03-09 10:24 ` Artem Bityutskiy
2012-03-09 16:10 ` Artem Bityutskiy
2012-03-09 21:11 ` Jan Kara
2012-03-12 12:36 ` Artem Bityutskiy
2012-03-12 14:02 ` Jan Kara
2012-03-12 14:21 ` Artem Bityutskiy
2012-03-09 10:15 ` Jan Kara
2012-03-09 15:10 ` Fengguang Wu
2012-02-29 13:51 ` [PATCH v2 " Fengguang Wu
2012-03-01 13:35 ` Fengguang Wu
2012-03-02 6:22 ` [PATCH v3 " Fengguang Wu
2012-02-28 14:00 ` [PATCH 6/9] vmscan: dirty reclaim throttling Fengguang Wu
2012-02-28 14:00 ` [PATCH 7/9] mm: pass __GFP_WRITE to memcg charge and reclaim routines Fengguang Wu
2012-02-28 14:00 ` [PATCH 8/9] mm: dont set __GFP_WRITE on ramfs/sysfs writes Fengguang Wu
2012-03-01 10:13 ` Johannes Weiner
2012-03-01 10:30 ` Fengguang Wu
2012-02-28 14:00 ` [PATCH 9/9] mm: debug vmscan waits Fengguang Wu
2012-03-02 6:59 ` [RFC PATCH] mm: don't treat anonymous pages as dirtyable pages Fengguang Wu
2012-03-02 7:18 ` Fengguang Wu
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