linux-kernel - Re: Is nobh code still useful?

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Date:	Thu, 17 Sep 2009 17:25:10 +0200
From:	Jan Kara <jack@...e.cz>
To:	Boaz Harrosh <bharrosh@...asas.com>
Cc:	Jan Kara <jack@...e.cz>, Nick Piggin <npiggin@...e.de>,
	linux-fsdevel@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>,
	pbadari@...ibm.com, Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: Is nobh code still useful?

On Thu 17-09-09 18:11:27, Boaz Harrosh wrote:
> On 09/17/2009 04:56 PM, Jan Kara wrote:
> >   Hi,
> > 
> >   during my page_mkwrite() work, I've looked at who uses nobh_ versions of
> > various functions in fs/buffer.c. It seems only ext2 and jfs use them. ext3
> > uses them only from writepage() (which means we needn't attach buffers to a
> > page when it was written via mmap in writeback mode) and ext4 tries to use
> > them but in fact it's nop because it always attaches buffers to the page
> > earlier. So it's not really widely used, there's quite some code to support
> > it (including one page flag), and it also slightly complicates my
> > page_mkwrite() fixes.
> >   So I wanted to ask does somebody actually remember what it is good for?
> > Buffer heads obviously consume some memory so was that the reason? OTOH we
> > have to map the page whenever we write to it or send it to disk via
> > writepage().
> > 
> > 								Honza
> 
> I'm currently using nobh_truncate_page() in fs/exofs/inode.c::exofs_truncate().
> 
> Though, I suspect that once I do the conversion to Nick's:
> 	"[patch 00/11] new truncate sequence" 
> and it is submitted, that use will disappear.
  Yeah, actually with page_mkwrite patches I've just sent, this would
definitely go away so this isn't a use I'm too much worried about ;). But
thanks for info anyway.

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