linux-kernel - Re: [PATCH 5/9] writeback: introduce the pageout work

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Message-ID: <20120312140229.GG5998@quack.suse.cz>
Date:	Mon, 12 Mar 2012 15:02:29 +0100
From:	Jan Kara <jack@...e.cz>
To:	Artem Bityutskiy <dedekind1@...il.com>
Cc:	Jan Kara <jack@...e.cz>, Fengguang Wu <fengguang.wu@...el.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Greg Thelen <gthelen@...gle.com>,
	Ying Han <yinghan@...gle.com>,
	"hannes@...xchg.org" <hannes@...xchg.org>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Rik van Riel <riel@...hat.com>, Mel Gorman <mgorman@...e.de>,
	Minchan Kim <minchan.kim@...il.com>,
	Linux Memory Management List <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Adrian Hunter <adrian.hunter@...el.com>
Subject: Re: [PATCH 5/9] writeback: introduce the pageout work

On Mon 12-03-12 14:36:14, Artem Bityutskiy wrote:
> On Fri, 2012-03-09 at 22:11 +0100, Jan Kara wrote:
> > On Fri 09-03-12 18:10:51, Artem Bityutskiy wrote:
> > > On Fri, 2012-03-09 at 10:51 +0100, Jan Kara wrote:
> > > > > However I cannot find any ubifs functions to form the above loop, so
> > > > > ubifs should be safe for now.
> > > >   Yeah, me neither but I also failed to find a place where
> > > > ubifs_evict_inode() truncates inode space when deleting the inode... Artem?
> > > 
> > > We do call 'truncate_inode_pages()':
> > > 
> > > static void ubifs_evict_inode(struct inode *inode)
> > > {
> > > 	...
> > > 
> > >         truncate_inode_pages(&inode->i_data, 0);
> > > 
> > >         ...
> > > }
> >   Well, but that just removes pages from page cache. You should somewhere
> > also free allocated blocks and free the inode... And I'm sure you do,
> > otherwise you would pretty quickly notice that file deletion does not work
> > :) Just I could not find which function does it.
> 
> ubifs_evict_inode() -> ubifs_jnl_delete_inode() ->
> ubifs_tnc_remove_ino()
> 
> Basically, deletion in UBIFS is about writing a so-called "deletion
> inode" to the journal and then removing all the data nodes of the
> truncated inode from the TNC (in-memory cache of the FS index, which is
> just a huge B-tree, like in reiser4 which inspired me long time ago, and
> like in btrfs).
> 
> The second part of the overall deletion job will be when we commit - the
> updated version of the FS index will be written to the flash media.
  Oh, I see. This is what I was missing. And I presume you always make sure
to have enough space for new FS index so it cannot deadlock when trying to
push out dirty pages.

> If we get a power cut before the commit, the journal reply will see the
> deletion inode and will clean-up the index. The deletion inode is never
> erased before the commit.
> 
> Basically, this design is dictated by the fact that we do not have a
> cheap way of doing in-place updates.
> 
> This is a short version of the story. Here are some docs as well:
> http://www.linux-mtd.infradead.org/doc/ubifs.html#L_documentation
  I see. Thanks.

								Honza
-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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