Improve cloning performance for large numbers of clones (LP: #1567557)

Bump zcmd buffer from 16K to 256K.

diff --git a/debian/patches/2000-increase-default-zcmd-allocation-to-256K.patch b/debian/patches/2000-increase-default-zcmd-allocation-to-256K.patch
new file mode 100644 (file)
index 0000000..c4e9f2e
--- /dev/null
+++ b/debian/patches/2000-increase-default-zcmd-allocation-to-256K.patch
@@ -0,0 +1,67 @@
+Increase default zcmd allocation to 256K (LP: #567557)
+
+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. This may sound large, but on 64 bit systems
+running ZFS this is not a huge chunk of memory for the speed
+improvement we gains for large sets of clones:
+
+        16K zcmd        256K zcmd
+Clones Time    Clones  Time    Clone   % improvement
+        (secs)         per sec (secs)  per sec
+100    7       14.29   5       20.00   28.57
+200    10      20.00   9       22.22   10.00
+300    19      15.79   18      16.67   5.26
+400    22      18.18   22      18.18   0.00
+500    29      17.24   29      17.24   0.00
+600    39      15.38   39      15.38   0.00
+700    46      15.22   45      15.56   2.17
+800    58      13.79   51      15.69   12.07
+900    74      12.16   61      14.75   17.57
+1000   90      11.11   74      13.51   17.78
+1100   98      11.22   87      12.64   11.22
+1200   102     11.76   95      12.63   6.86
+1300   113     11.50   104     12.50   7.96
+1400   143     9.79    109     12.84   23.78
+1500   145     10.34   132     11.36   8.97
+1600   165     9.70    145     11.03   12.12
+1700   187     9.09    156     10.90   16.58
+1800   210     8.57    166     10.84   20.95
+1900   226     8.41    183     10.38   19.03
+2000   256     7.81    198     10.10   22.66
+2200   311     7.07    238     9.24    23.47
+2400   373     6.43    271     8.86    27.35
+2600   487     5.34    316     8.23    35.11
+3000   619     4.85    426     7.04    31.18
+3400   915     3.72    549     6.19    40.00
+4000   1332    3.00    923     4.33    30.71
+
+As one can see, with > 2000 clones we get 25-40% speed
+improvement.
+
+This patch was originally suggested by Brian Behlendorf
+(see https://github.com/zfsonlinux/zfs/issues/6372), however
+this fix is a more generic fix to cover all zcmd cases.
+
+Signed-off-by: Colin Ian King <colin.king@canonical.com>
+
+Index: zfs/lib/libzfs/libzfs_util.c
+===================================================================
+--- zfs.orig/lib/libzfs/libzfs_util.c
++++ zfs/lib/libzfs/libzfs_util.c
+@@ -1354,7 +1354,7 @@ 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);

diff --git a/debian/patches/series b/debian/patches/series
index d6f6f87f925089e691d551d9529924e4624c43d2..6d5874440d037cfc3bc9e3ee4002c68ec66a7670 100644 (file)
--- a/debian/patches/series
+++ b/debian/patches/series
@@ -7,3 +7,4 @@ enable-zed.patch
 0008-dracut-make-module-setup.sh-shebang-explicit.patch
 0009-add-man-page-reference-to-systemd-units.patch
 0010-fix-install-path-of-zpool.d-scripts.patch
+2000-increase-default-zcmd-allocation-to-256K.patch