Re: Re[2]: [PATCH 07/11] md: rewrite handle_stripe_dirtying6 in asynchronous way

On Fri, Jan 16, 2009 at 7:24 AM, Yuri Tikhonov [off-list ref] wrote:

quoted

Ok, I now see why this change was made.  Please make this changelog
more descriptive than "Rewrite handle_stripe_dirtying6 function to
work asynchronously."

 Sure, how about the following:

"

 md: rewrite handle_stripe_dirtying6 in asynchronous way

 Processing stripe dirtying in asynchronous way requires some changes
to the handle_stripe_dirtying6() algorithm.

 In the synchronous implementation of the stripe dirtying we processed
dirtying of a degraded stripe (with partially changed strip(s) located
on the failed drive(s)) inside one handle_stripe_dirtying6() call:
- we computed the missed strips from the old parities, and thus got
the fully up-to-date stripe, then
- we did reconstruction using the new data to write.

 In the asynchronous case of handle_stripe_dirtying6() we don't
process anything right inside this function (since we under the lock),
but only schedule the necessary operations with flags. Thus, if
handle_stripe_dirtying6() is performed on the top of a degraded array
we should schedule the reconstruction operation when the failed strips
are marked (by previously called fetch_block6()) as to be computed
(with the R5_Wantcompute flag), and all the other strips of the stripe
are UPTODATE. The schedule_reconstruction() function will set the
STRIPE_OP_POSTXOR flag [for new parity calculation], which is then
handled in raid_run_ops() after the STRIPE_OP_COMPUTE_BLK one [which
causes computing of the data missed].

"

Excellent!

Thanks,
Dan