debian/patches/2000-increase-default-zcmd-allocation-to-256K.patch

   1 Increase default zcmd allocation to 256K (LP: #567557)
   2
   3 When creating hundreds of clones (for example using containers with
   4 LXD) cloning slows down as the number of clones increases over time.
   5 The reason for this is that the fetching of the clone information
   6 using a small zcmd buffer requires two ioctl calls, one to determine
   7 the size and a second to return the data. However, this requires
   8 gathering the data twice, once to determine the size and again to
   9 populate the zcmd buffer to return it to userspace.
  10
  11 These are expensive ioctl() calls, so instead, make the default buffer
  12 size much larger: 256K. This may sound large, but on 64 bit systems
  13 running ZFS this is not a huge chunk of memory for the speed
  14 improvement we gains for large sets of clones:
  15
  16         16K zcmd        256K zcmd
  17 Clones  Time    Clones  Time    Clone   % improvement
  18         (secs)  per sec (secs)  per sec
  19 100     7       14.29   5       20.00   28.57
  20 200     10      20.00   9       22.22   10.00
  21 300     19      15.79   18      16.67   5.26
  22 400     22      18.18   22      18.18   0.00
  23 500     29      17.24   29      17.24   0.00
  24 600     39      15.38   39      15.38   0.00
  25 700     46      15.22   45      15.56   2.17
  26 800     58      13.79   51      15.69   12.07
  27 900     74      12.16   61      14.75   17.57
  28 1000    90      11.11   74      13.51   17.78
  29 1100    98      11.22   87      12.64   11.22
  30 1200    102     11.76   95      12.63   6.86
  31 1300    113     11.50   104     12.50   7.96
  32 1400    143     9.79    109     12.84   23.78
  33 1500    145     10.34   132     11.36   8.97
  34 1600    165     9.70    145     11.03   12.12
  35 1700    187     9.09    156     10.90   16.58
  36 1800    210     8.57    166     10.84   20.95
  37 1900    226     8.41    183     10.38   19.03
  38 2000    256     7.81    198     10.10   22.66
  39 2200    311     7.07    238     9.24    23.47
  40 2400    373     6.43    271     8.86    27.35
  41 2600    487     5.34    316     8.23    35.11
  42 3000    619     4.85    426     7.04    31.18
  43 3400    915     3.72    549     6.19    40.00
  44 4000    1332    3.00    923     4.33    30.71
  45
  46 As one can see, with > 2000 clones we get 25-40% speed
  47 improvement.
  48
  49 This patch was originally suggested by Brian Behlendorf
  50 (see https://github.com/zfsonlinux/zfs/issues/6372), however
  51 this fix is a more generic fix to cover all zcmd cases.
  52
  53 Signed-off-by: Colin Ian King <colin.king@canonical.com>
  54
  55 Index: zfs/lib/libzfs/libzfs_util.c
  56 ===================================================================
  57 --- zfs.orig/lib/libzfs/libzfs_util.c
  58 +++ zfs/lib/libzfs/libzfs_util.c
  59 @@ -1354,7 +1354,7 @@ int
  60  zcmd_alloc_dst_nvlist(libzfs_handle_t *hdl, zfs_cmd_t *zc, size_t len)
  61  {
  62         if (len == 0)
  63 -               len = 16 * 1024;
  64 +               len = 256 * 1024;
  65         zc->zc_nvlist_dst_size = len;
  66         zc->zc_nvlist_dst =
  67             (uint64_t)(uintptr_t)zfs_alloc(hdl, zc->zc_nvlist_dst_size);