Re: [RFC] block integrity: Fix write after checksum calculationproblem
From: Jan Kara
Date: Thu Feb 24 2011 - 11:43:46 EST
On Wed 23-02-11 11:24:50, Martin K. Petersen wrote:
> >>>>> "Dave" == Dave Chinner <david@xxxxxxxxxxxxx> writes:
> >> Agreed. I too am curious to study which circumstances favor copying
> >> vs blocking.
> Dave> IMO blocking is generally preferable in high throughput threaded
> Dave> workloads as there is always another thread that can do useful
> Dave> work while we wait for IO to complete. Most use cases for DIF
> Dave> center around high throughput environments....
> A while back I did a bunch of tests with a liberal amount of
> wait_on_page_writeback() calls added to (I think) ext2, ext3, and
> XFS. For my regular workloads there was no measurable change (kernel
> builds, random database and I/O tests). I'm sure we'll unearth some apps
> that will suffer when DI is on but so far I'm not too worried about
> blocking in the data path.
> My main concern is wrt. metadata because that's where extN really
> hurts. Simple test: Unpack a kernel tarball and watch the directory
> block fireworks. Given how frequently those buffers get hit I'm sure
> blocking would cause performance to tank completely. I looked into
> fixing this in ext2 but I had to stop because my eyes were bleeding.
Ext2 is problematic yes, but ext should be OK because we do
metadata copy anyway because of journalling. So for ext you shouldn't
need any additional metadata protection since JBD does it for you (apart
from nojournal mode of ext4 of course).
Jan Kara <jack@xxxxxxx>
SUSE Labs, CR
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/