From: Michael Niewöhner Date: Tue, 30 Jul 2019 16:59:38 +0000 (+0200) Subject: Increase default zcmd allocation to 256K X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=85ce79bbc8cf17f100eb4ae6a0d1b1ce2e2dd9d9;p=zfs Increase default zcmd allocation to 256K 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 Reviewed-by: George Melikov Signed-off-by: Colin Ian King Signed-off-by: Michael Niewöhner Closes #9084 --- diff --git a/lib/libzfs/libzfs_util.c b/lib/libzfs/libzfs_util.c index 9dcbb9b60..27d630d4f 100644 --- a/lib/libzfs/libzfs_util.c +++ b/lib/libzfs/libzfs_util.c @@ -1140,7 +1140,7 @@ 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);