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.... > > Yeah. > > 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[34] should be OK because we do metadata copy anyway because of journalling. So for ext[34] you shouldn't need any additional metadata protection since JBD does it for you (apart from nojournal mode of ext4 of course). Honza -- Jan Kara <jack@xxxxxxx> SUSE Labs, CR -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
