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Increase default zcmd allocation to 256K

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When creating hundreds of clones (for example using containers with
LXD) cloning slows down as the number of clones increases over time.
The reason for this is that the fetching of the clone information
using a small zcmd buffer requires two ioctl calls, one to determine
the size and a second to return the data. However, this requires
gathering the data twice, once to determine the size and again to
populate the zcmd buffer to return it to userspace.
These are expensive ioctl() calls, so instead, make the default buffer
size much larger: 256K.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: George Melikov <mail@gmelikov.ru>
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Michael Niewöhner <foss@mniewoehner.de>
Closes #9084
This commit is contained in:
Michael Niewöhner 2019-07-30 18:59:38 +02:00 committed by Tony Hutter
parent 6c9882d5db
commit 6d1599c1e1
1 changed files with 1 additions and 1 deletions
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2
lib/libzfs/libzfs_util.c
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@ -1139,7 +1139,7 @@ int
zcmd_alloc_dst_nvlist(libzfs_handle_t *hdl, zfs_cmd_t *zc, size_t len)
{
if (len == 0)
len = 16 * 1024;
len = 256 * 1024;
zc->zc_nvlist_dst_size = len;
zc->zc_nvlist_dst =
(uint64_t)(uintptr_t)zfs_alloc(hdl, zc->zc_nvlist_dst_size);