linux-kernel - Re: [PATCH 1/3] block_write_full_page: Use synchronous writes for WBC_SYNC

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Message-ID: <20090407141904.GD31725@mit.edu>
Date:	Tue, 7 Apr 2009 10:19:04 -0400
From:	Theodore Tso <tytso@....edu>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Jens Axboe <jens.axboe@...cle.com>,
	Linux Kernel Developers List <linux-kernel@...r.kernel.org>,
	Ext4 Developers List <linux-ext4@...r.kernel.org>,
	jack@...e.cz
Subject: Re: [PATCH 1/3] block_write_full_page: Use synchronous writes for
	WBC_SYNC_ALL writebacks

On Tue, Apr 07, 2009 at 12:23:13AM -0700, Andrew Morton wrote:
> 
> I think the number of different greps which was needed to find all the
> above was excessive.  Too many levels of wrappers and helpers.

This is true not only for the block I/O code, it's true also for the
page writeback code --- have you ever tried creating a call tree that
traces all of the descendents of sync_inode()?

One of these days when I have a spare week (hah!), I'd love to create
a huge chart of all of the callers into the various wrapper functions
of the page writeback paths, figure out who needs what, and then
collapse the rest.

> > It looks like a good candidate for WRITE_SYNC_PLUG instead,

Yeah, what we'll need to do now that we have the difference between
WRITE_SYNC and WRITE_SYNC_PLUG is to have a way of signalling
(probably via yet another wbc flag) that we want WRITE_SYNC_PLUG and
not WRITE_SYNC, and that the top-level caller of this whole mess will
be responsible for issuing the unplug.  I'll try to get something
whipped up.

						- Ted

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