Re: Linux 2.4.21-pre1

[Matthias Andree]

On Tue, 10 Dec 2002, Marcelo Tosatti wrote:

> So here goes the first pre of 2.4.21 including the new IDE code merged
> from Alan's tree.
> 
> Test it carefully, since the new IDE code is not yet fully tested.
> 
> Do not use it with critical data.

Oh, speaking of "carefully", could Andrew Morton's mount -o dirsync
feature patch for 2.4.21 please be merged early in v2.4.21-pre? User
space (util-linux, e2fsprogs' lsattr/chattr) has been supporting it for
a while, just the kernel lacked it.

This -o dirsync feature is necessary to give applications that are
either unaware of Linux' default -o async or that do not want to cater
for deliberate incompatibilities a big performance boost: these
applications (Postfix on ext2fs but not on 2.4 ext3fs or reiserfs, qmail
on any Linux fs, probably a lot others I haven't even looked at)
traditionally *require* chattr +S or mount -o sync to work reliably,
after the merge, they could instead go with mount -o dirsync or chattr
+D, which improves write speed quite a bit.

Not applying the dirsync patch means that a stupid BSD ffs in default
configuration will beat Linux (that needs -o sync) hands-down without
any tuning the admin could do. One might also consider making -o dirsync
the default while one's there, to give users a default-reliable setting,
but this is going to rouse the performance fetishists who don't care
about data persistence and who don't care to collect their new files
from lost+found on ext2fs but rather cheat benchmarks.

I can elaborate a bit more, but this has been discussed multiple times
and after all, the code is there.

> Summary of changes from v2.4.20 to v2.4.21-pre1

...