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

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Date:	Mon, 12 Mar 2012 14:36:14 +0200
From:	Artem Bityutskiy <dedekind1@...il.com>
To:	Jan Kara <jack@...e.cz>
Cc:	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 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.

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

-- 
Best Regards,
Artem Bityutskiy

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