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| H A D | parallels.c | d6179011 Tue Apr 28 07:46:58 GMT 2015 Denis V. Lunev <den@openvz.org> block/parallels: add prealloc-mode and prealloc-size open paramemets
This is preparational commit for tweaks in Parallels image expansion.
The idea is that enlarge via truncate by one data block is slow. It
would be much better to use fallocate via bdrv_write_zeroes and
expand by some significant amount at once.
Original idea with sequential file writing to the end of the file without
fallocate/truncate would be slower than this approach if the image is
expanded with several operations:
- each image expanding means file metadata update, i.e. filesystem
journal write. Truncate/write to newly truncated space update file
metadata twice thus truncate removal helps. With fallocate call
inside bdrv_write_zeroes file metadata is updated only once and
this should happen infrequently thus this approach is the best one
for the image expansion
- tail writes are ordered, i.e. the guest IO queue could not be sent
immediately to the host introducing additional IO delays
This patch just adds proper parameters into BDRVParallelsState and
performs options parsing in parallels_open.
Signed-off-by: Denis V. Lunev <den@openvz.org>
Reviewed-by: Roman Kagan <rkagan@parallels.com>
Signed-off-by: Roman Kagan <rkagan@parallels.com>
Message-id: 1430207220-24458-26-git-send-email-den@openvz.org
CC: Roman Kagan <rkagan@parallels.com>
CC: Kevin Wolf <kwolf@redhat.com>
CC: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
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