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Date: Thu, 15 Nov 2001 23:05:14 +0000
From: "Stephen C. Tweedie" <sct@redhat.com>
To: Andrew Morton <akpm@zip.com.au>
Cc: "Stephen C. Tweedie" <sct@redhat.com>, lkml <linux-kernel@vger.kernel.org>,
        Neil Brown <neilb@cse.unsw.edu.au>
Subject: Re: synchronous mounts
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In-Reply-To: <3BF43B8E.51A809D1@zip.com.au>; from akpm@zip.com.au on Thu, Nov 15, 2001 at 02:02:54PM -0800
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Hi,

On Thu, Nov 15, 2001 at 02:02:54PM -0800, Andrew Morton wrote:
> 
> So shall we try to nail this down?  Synchronous mounts and chattr +S
> provide synchronous semantics for directory contents, diretory metadata
> and directory inodes only.  And fsync() will write out a file's data,
> metadata and inode?

Sounds sane.  UFS sync mounts also update the inode bitmaps
synchronously, and in order, so that they can tell exactly when an
inode is valid.  I guess that we don't need that, at least on ext2,
since the i_dtime gives us the necessary information automatically.

> If this is correct then there are a few places where ext2 is
> syncing stuff unnecessarily - file indirect blocks, etc.  Not
> very important at this stage I guess.

It's important for people running MTAs which expect dir sync
behaviour: admins have to pay the performance cost of all file updates
being sync as well as the directory updates if they enable chattr +S
on the dir.

--Stephen
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