Tony Nguyen 64b6c47d90 dbuf_hold_impl() cleanup to improve cached read performance ... Currently every dbuf_hold_impl() incurs kmem_alloc() and kmem_free() which can be costly for cached read performance. This change reverts the dbuf_hold_impl() fix stack commit, i.e. fc5bb51f08 to eliminate the extra kmem_alloc() and kmem_free() operations and improve cached read performance. With the change, each dbuf_hold_impl() frame uses 40 bytes more, total of 800 for 20 recursive levels. Linux kernel stack sizes are 8K and 16K for 32bit and 64bit, respectively, so stack overrun risk is limited. Sample stack output comparisons with 50 PB file and recordsize=512 Current code 11) 2240 64 arc_alloc_buf+0x4a/0xd0 [zfs] 12) 2176 264 dbuf_read_impl.constprop.16+0x2e3/0x7f0 [zfs] 13) 1912 120 dbuf_read+0xe5/0x520 [zfs] 14) 1792 56 dbuf_hold_impl_arg+0x572/0x630 [zfs] 15) 1736 64 dbuf_hold_impl_arg+0x508/0x630 [zfs] 16) 1672 64 dbuf_hold_impl_arg+0x508/0x630 [zfs] 17) 1608 40 dbuf_hold_impl+0x23/0x40 [zfs] 18) 1568 40 dbuf_hold_level+0x32/0x60 [zfs] 19) 1528 16 dbuf_hold+0x16/0x20 [zfs] dbuf_hold_impl() cleanup 11) 2320 64 arc_alloc_buf+0x4a/0xd0 [zfs] 12) 2256 264 dbuf_read_impl.constprop.17+0x2e3/0x7f0 [zfs] 13) 1992 120 dbuf_read+0xe5/0x520 [zfs] 14) 1872 96 dbuf_hold_impl+0x50f/0x5e0 [zfs] 15) 1776 104 dbuf_hold_impl+0x4df/0x5e0 [zfs] 16) 1672 104 dbuf_hold_impl+0x4df/0x5e0 [zfs] 17) 1568 40 dbuf_hold_level+0x32/0x60 [zfs] 18) 1528 16 dbuf_hold+0x16/0x20 [zfs] Performance observations on 8K recordsize filesystem: - 8/128/1024K at 1-128 sequential cached read, ~3% improvement Testing done on Ubuntu 18.04 with 4.15 kernel, 8vCPUs and SSD storage on VMware ESX. Reviewed-by: Matt Ahrens <matt@delphix.com> Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov> Signed-off-by: Tony Nguyen <tony.nguyen@delphix.com> Closes #9351		2019-10-03 15:33:38 -07:00
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avl	Fix typos in module/	2019-08-30 14:32:18 -07:00
icp	OpenZFS restructuring - move platform specific headers	2019-09-05 09:34:54 -07:00
lua	Fix typos in module/	2019-08-30 14:32:18 -07:00
nvpair	Fix typos in module/	2019-08-30 14:32:18 -07:00
os	Timeout waiting for ZVOL device to be created	2019-10-01 12:33:12 -07:00
spl	OpenZFS restructuring - move platform specific sources	2019-09-06 11:26:26 -07:00
unicode	Update build system and packaging	2018-05-29 16:00:33 -07:00
zcommon	Make module tunables cross platform	2019-09-05 14:49:49 -07:00
zfs	dbuf_hold_impl() cleanup to improve cached read performance	2019-10-03 15:33:38 -07:00
.gitignore	Prepare SPL repo to merge with ZFS repo	2018-05-29 14:51:39 -07:00
Makefile.in	OpenZFS restructuring - move platform specific sources	2019-09-06 11:26:26 -07:00