linux-ext4 - Re: [PATCH 2/2] ext4: journal superblock modifications in ext4

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Date:	Sun, 08 Nov 2009 16:09:40 -0600
From:	Eric Sandeen <sandeen@...hat.com>
To:	Theodore Tso <tytso@....edu>
CC:	Andreas Dilger <adilger@....com>,
	ext4 development <linux-ext4@...r.kernel.org>
Subject: Re: [PATCH 2/2] ext4: journal superblock modifications in	ext4_statfs()

Theodore Tso wrote:
> On Fri, Nov 06, 2009 at 05:26:51PM -0700, Andreas Dilger wrote:
>> If the choice is between adding a proper transaction here, or not
>> doing this at all, I'd rather just not do it at all.  Of course, I'd
>> like to work out some kind of compromise, like only updating the
>> superblock when there is already a shadow BH that is being used to
>> write to the journal, or similar.
> 
> In practice, the superblock is never going to modified in normal
> operations, unless a resize happens to be happening.  Since we already
> force the superblock summary counters to be correct during an unmount
> or file system freeze, we really only need this so that it's correct
> after a file system crash.
> 
> I don't think people generally end up calling statfs() all that
> frequently, so it's not clear how much adding a 30 second throttle
> would help.  Maybe we should just not bother trying to update the
> superblock at all on a statfs()?

for now maybe that's better....

But don't we journal the superblock sometimes, not others ... for 
example write_super -> ext4_write_super -> ext4_commit_super does no 
journaling of superblock modifications. ext4_orphan_add, however, does. 
  This would likely lead to trouble w/ the debugging patch ... though I 
didn't see it ... ?

So I was premature w/ this patch, I think.

Maybe we could unconditionally do the copy-out in 
jbd2_journal_write_metadata_buffer() ...?

-Eric

> Hmm...
> 
> 						- Ted

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