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

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Message-ID: <4AB2519F.8020409@panasas.com>
Date:	Thu, 17 Sep 2009 18:11:27 +0300
From:	Boaz Harrosh <bharrosh@...asas.com>
To:	Jan Kara <jack@...e.cz>, Nick Piggin <npiggin@...e.de>
CC:	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 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.

Thanks
Boaz
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