Re: [PATCH 1/5] ext4: Avoid races caused by on-line resizing andSMP memory reordering

[Theodore Tso]

On Tue, Apr 28, 2009 at 06:23:59PM +0200, Jan Kara wrote:
>   Ouch... Hmm, smp_rmb() isn't completely free and mainly it's a bit
> ugly and prone to errors (I'm afraid next time someone changes the
> allocation code, we miss some barriers again)... so.. Maybe a stupid
> idea but wouldn't it be easier to solve the online resize like: freeze
> the filesystem, do all the changes required for extend, unfreeze the
> filesystem?

Eric suggested a helper function when reading from s_groups_count.
That would take care of the code maintenance headache.  One problem
with using freeze/thaw is it won't work without a journal, and we do
support filesystems without journals in ext4.  (Probably the best
solution for netbooks with crapola SSD's.)

As far as smb_rmb() not being free, it's essentially free for
x86/x86_64 platforms.  Is it really that costly on other
architectures?

						- Ted
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