On 07/28/2016 03:32 PM, Niels de Vos
wrote:
There are some features in QEMU that we could implement with the existing libgfapi functions. Kevin asked me about this a while back, and I have finally (sorry for the delay Kevin!) taken the time to look into it. There are some optional operations that can be set in the BlockDriver structure. The ones missing that we could have, or have useless implementations are these: .bdrv_get_info/.bdrv_refresh_limits: This seems to set values in a BlockDriverInfo and BlockLimits structure that is used by QEMUs block layer. By setting the right values, we can use glfs_discard() and glfs_zerofill() to reduce the writing of 0-bytes that QEMU falls back on at the moment. .bdrv_has_zero_init / qemu_gluster_has_zero_init: Currently always returns 0. But if a file gets created on a Gluster volume, it should never have old contents in it. Rewriting it with 0-bytes looks unneeded to me. N00b question, what is the need for separate glfs_discard() and glfs_zerofill() functions? Can we not just use glfs_fallocate() with appropriate flags? posix_discard() in gluster seems to be using fallocate() with FALLOC_FL_PUNCH_HOLE flag. And posix_zerofill() can be made smarter to use FALLOC_FL_ZERO_RANGE and fallback to writing zeroes if ZERO_RANGE is not supported. Regards, Ravi With these improvements the gluster:// URL usage with QEMU (and now also the new JSON QAPI), certain operations are expected to be a little faster. Anyone starting to work on this would want to trace the actual operations (on a single-brick volume) with ltrace/wireshark on the system where QEMU runs. Who is interested to take this on? Niels
|
_______________________________________________ Gluster-devel mailing list Gluster-devel@xxxxxxxxxxx http://www.gluster.org/mailman/listinfo/gluster-devel