From 9965059ab9991a5fc7df9a489021e73880b3bcc0 Mon Sep 17 00:00:00 2001 From: Brian Behlendorf Date: Tue, 18 Aug 2015 13:51:20 -0700 Subject: [PATCH] Prefetch start and end of volumes When adding a zvol to the system prefetch zvol_prefetch_bytes from the start and end of the volume. Prefetching these regions of the volume is desirable because they are likely to be accessed immediately by blkid(8), the kernel scanning for a partition table, or another task which probes the devices. Signed-off-by: Richard Yao Signed-off-by: Brian Behlendorf Issue #3659 --- man/man5/zfs-module-parameters.5 | 15 +++++++++++++++ module/zfs/zvol.c | 17 +++++++++++++++++ 2 files changed, 32 insertions(+) diff --git a/man/man5/zfs-module-parameters.5 b/man/man5/zfs-module-parameters.5 index 6d4a8c304..015ab0186 100644 --- a/man/man5/zfs-module-parameters.5 +++ b/man/man5/zfs-module-parameters.5 @@ -1631,6 +1631,21 @@ Max number of blocks to discard at once Default value: \fB16,384\fR. .RE +.sp +.ne 2 +.na +\fBzvol_prefetch_bytes\fR (uint) +.ad +.RS 12n +When adding a zvol to the system prefetch \fBzvol_prefetch_bytes\fR +from the start and end of the volume. Prefetching these regions +of the volume is desirable because they are likely to be accessed +immediately by \fBblkid(8)\fR or by the kernel scanning for a partition +table. +.sp +Default value: \fB131,072\fR. +.RE + .SH ZFS I/O SCHEDULER ZFS issues I/O operations to leaf vdevs to satisfy and complete I/Os. The I/O scheduler determines when and in what order those operations are diff --git a/module/zfs/zvol.c b/module/zfs/zvol.c index 7c1f024ca..bcdd8e8de 100644 --- a/module/zfs/zvol.c +++ b/module/zfs/zvol.c @@ -50,6 +50,7 @@ unsigned int zvol_inhibit_dev = 0; unsigned int zvol_major = ZVOL_MAJOR; +unsigned int zvol_prefetch_bytes = (128 * 1024); unsigned long zvol_max_discard_blocks = 16384; static kmutex_t zvol_state_lock; @@ -1296,6 +1297,7 @@ __zvol_create_minor(const char *name, boolean_t ignore_snapdev) objset_t *os; dmu_object_info_t *doi; uint64_t volsize; + uint64_t len; unsigned minor = 0; int error = 0; @@ -1369,6 +1371,18 @@ __zvol_create_minor(const char *name, boolean_t ignore_snapdev) zil_replay(os, zv, zvol_replay_vector); } + /* + * When udev detects the addition of the device it will immediately + * invoke blkid(8) to determine the type of content on the device. + * Prefetching the blocks commonly scanned by blkid(8) will speed + * up this process. + */ + len = MIN(MAX(zvol_prefetch_bytes, 0), SPA_MAXBLOCKSIZE); + if (len > 0) { + dmu_prefetch(os, ZVOL_OBJ, 0, len); + dmu_prefetch(os, ZVOL_OBJ, volsize - len, len); + } + zv->zv_objset = NULL; out_dmu_objset_disown: dmu_objset_disown(os, zvol_tag); @@ -1625,3 +1639,6 @@ MODULE_PARM_DESC(zvol_major, "Major number for zvol device"); module_param(zvol_max_discard_blocks, ulong, 0444); MODULE_PARM_DESC(zvol_max_discard_blocks, "Max number of blocks to discard"); + +module_param(zvol_prefetch_bytes, uint, 0644); +MODULE_PARM_DESC(zvol_prefetch_bytes, "Prefetch N bytes at zvol start+end");