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Matthew Ahrens 8805abb8fc single-chunk scatter ABDs can be treated as linear 
Scatter ABD's are allocated from a number of pages.  In contrast to
linear ABD's, these pages are disjoint in the kernel's virtual address
space, so they can't be accessed as a contiguous buffer.  Therefore
routines that need a linear buffer (e.g. abd_borrow_buf() and friends)
must allocate a separate linear buffer (with zio_buf_alloc()), and copy
the contents of the pages to/from the linear buffer.  This can have a
measurable performance overhead on some workloads.

https://github.com/zfsonlinux/zfs/commit/87c25d567fb7969b44c7d8af63990e
("abd_alloc should use scatter for >1K allocations") increased the use
of scatter ABD's, specifically switching 1.5K through 4K (inclusive)
buffers from linear to scatter.  For workloads that access blocks whose
compressed sizes are in this range, that commit introduced an additional
copy into the read code path.  For example, the
sequential_reads_arc_cached tests in the test suite were reduced by
around 5% (this is doing reads of 8K-logical blocks, compressed to 3K,
which are cached in the ARC).

This commit treats single-chunk scattered buffers as linear buffers,
because they are contiguous in the kernel's virtual address space.

All single-page (4K) ABD's can be represented this way.  Some multi-page
ABD's can also be represented this way, if we were able to allocate a
single "chunk" (higher-order "page" which represents a power-of-2 series
of physically-contiguous pages).  This is often the case for 2-page (8K)
ABD's.

Representing a single-entry scatter ABD as a linear ABD has the
performance advantage of avoiding the copy (and allocation) in
abd_borrow_buf_copy / abd_return_buf_copy.  A performance increase of
around 5% has been observed for ARC-cached reads (of small blocks which
can take advantage of this), fixing the regression introduced by
87c25d567.

Note that this optimization is only possible because all physical memory
is always mapped into the kernel's address space.  This is not the case
for HIGHMEM pages, so the optimization can not be made on 32-bit
systems.

Reviewed-by: Chunwei Chen <tuxoko@gmail.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Matthew Ahrens <mahrens@delphix.com>
Closes #8580
 		2020-01-22 13:48:56 -08:00
..
crypto Add support for selecting encryption backend 2018-08-02 11:59:24 -07:00
fm Add zpool status -s (slow I/Os) and -p (parseable) 2018-11-08 16:47:24 -08:00
fs Race condition between spa async threads and export 2019-09-25 11:27:50 -07:00
lua Fix coverity defects: zfs channel programs 2018-02-20 11:19:42 -08:00
sysevent Add TRIM support 2019-03-29 09:13:20 -07:00
Makefile.am Add TRIM support 2019-03-29 09:13:20 -07:00
abd.h single-chunk scatter ABDs can be treated as linear 2020-01-22 13:48:56 -08:00
aggsum.h OpenZFS 8484 - Implement aggregate sum and use for arc counters 2018-06-06 09:35:59 -07:00
arc.h Linux 4.19-rc3+ compat: Remove refcount_t compat 2018-09-26 10:29:26 -07:00
arc_impl.h Linux 4.19-rc3+ compat: Remove refcount_t compat 2018-09-26 10:29:26 -07:00
avl.h Remove dead code from AVL tree 2017-10-05 19:28:00 -07:00
avl_impl.h Support custom build directories and move includes 2010-09-08 12:38:56 -07:00
blkptr.h OpenZFS 8067 - zdb should be able to dump literal embedded block pointer 2017-07-07 11:28:01 -07:00
bplist.h Support custom build directories and move includes 2010-09-08 12:38:56 -07:00
bpobj.h OpenZFS 7614, 9064 - zfs device evacuation/removal 2018-04-14 12:16:17 -07:00
bptree.h Illumos 4914 - zfs on-disk bookmark structure should be named *_phys_t 2014-08-06 14:48:41 -07:00
bqueue.h Illumos 5960, 5925 2016-01-08 15:08:19 -08:00
cityhash.h OpenZFS 8484 - Implement aggregate sum and use for arc counters 2018-06-06 09:35:59 -07:00
dataset_kstats.h port async unlinked drain from illumos-nexenta 2019-02-12 10:41:15 -08:00
dbuf.h Linux 4.19-rc3+ compat: Remove refcount_t compat 2018-09-26 10:29:26 -07:00
ddt.h Incorrect maximum DVA value in DDE_GET_NDVAS() 2018-02-26 14:20:12 -08:00
dmu.h Fix send/recv lost spill block 2019-05-07 15:18:44 -07:00
dmu_impl.h Fix send/recv lost spill block 2019-05-07 15:18:44 -07:00
dmu_objset.h Pool allocation classes 2018-09-05 18:33:36 -07:00
dmu_recv.h Fix send/recv lost spill block 2019-05-07 15:18:44 -07:00
dmu_send.h Refactor dmu_recv into its own file 2018-10-09 14:05:13 -07:00
dmu_traverse.h Native Encryption for ZFS on Linux 2017-08-14 10:36:48 -07:00
dmu_tx.h Linux 4.19-rc3+ compat: Remove refcount_t compat 2018-09-26 10:29:26 -07:00
dmu_zfetch.h OpenZFS 6322 - ZFS indirect block predictive prefetch 2016-08-30 14:26:55 -07:00
dnode.h Fix zil replay panic when TX_REMOVE followed by TX_CREATE 2019-09-25 11:27:51 -07:00
dsl_bookmark.h Fix comments on zfs_bookmark_phys 2019-09-25 11:27:48 -07:00
dsl_crypt.h Allow unencrypted children of encrypted datasets 2019-09-25 11:27:48 -07:00
dsl_dataset.h Detect and prevent mixed raw and non-raw sends 2019-03-13 11:00:43 -07:00
dsl_deadlist.h OpenZFS 7614, 9064 - zfs device evacuation/removal 2018-04-14 12:16:17 -07:00
dsl_deleg.h OpenZFS 7614, 9064 - zfs device evacuation/removal 2018-04-14 12:16:17 -07:00
dsl_destroy.h OpenZFS 7431 - ZFS Channel Programs 2018-02-08 15:28:18 -08:00
dsl_dir.h Remove duplicate macro in dsl_dir.h 2018-10-01 10:40:11 -07:00
dsl_pool.h port async unlinked drain from illumos-nexenta 2019-02-12 10:41:15 -08:00
dsl_prop.h Illumos 6171 - dsl_prop_unregister() slows down dataset eviction. 2016-01-12 10:53:12 -08:00
dsl_scan.h OpenZFS 7614, 9064 - zfs device evacuation/removal 2018-04-14 12:16:17 -07:00
dsl_synctask.h OpenZFS 9166 - zfs storage pool checkpoint 2018-06-26 10:07:42 -07:00
dsl_userhold.h Illumos #3740 2013-11-04 11:17:48 -08:00
edonr.h OpenZFS 4185 - add new cryptographic checksums to ZFS: SHA-512, Skein, Edon-R 2016-10-03 14:51:15 -07:00
efi_partition.h Fix spelling 2017-01-03 11:31:18 -06:00
frame.h Suppress incorrect objtool warnings 2017-12-07 10:28:50 -08:00
hkdf.h Encryption patch follow-up 2017-10-11 16:54:48 -04:00
metaslab.h Allow metaslab to be unloaded even when not freed from 2019-09-25 11:27:47 -07:00
metaslab_impl.h Add TRIM support 2019-03-29 09:13:20 -07:00
mmp.h MMP interval and fail_intervals in uberblock 2019-03-21 12:47:57 -07:00
mntent.h Make zfs mount according to relatime config in dataset 2016-04-05 18:55:59 -07:00
multilist.h Avoid extra taskq_dispatch() calls by DMU 2019-09-25 11:27:48 -07:00
note.h Update build system and packaging 2018-05-29 16:00:33 -07:00
nvpair.h Add new fnvlist_lookup_* functions 2018-10-03 15:30:55 -07:00
nvpair_impl.h OpenZFS 9580 - Add a hash-table on top of nvlist to speed-up operations 2018-07-30 11:30:03 -07:00
pathname.h Disable unused pathname::pn_path* (unneeded in Linux) 2019-09-25 11:27:49 -07:00
policy.h Add `zfs allow` and `zfs unallow` support 2016-06-07 09:16:52 -07:00
range_tree.h Rename range_tree_verify to range_tree_verify_not_present 2019-01-25 09:51:24 -08:00
refcount.h Add zfs_refcount_transfer_ownership_many() 2018-10-09 10:05:48 -07:00
rrwlock.h Linux 4.19-rc3+ compat: Remove refcount_t compat 2018-09-26 10:29:26 -07:00
sa.h Project Quota on ZFS 2018-02-13 14:54:54 -08:00
sa_impl.h Linux 4.19-rc3+ compat: Remove refcount_t compat 2018-09-26 10:29:26 -07:00
sdt.h Add line info and SET_ERROR() to ZFS debug log 2017-07-25 23:09:48 -07:00
sha2.h OpenZFS 4185 - add new cryptographic checksums to ZFS: SHA-512, Skein, Edon-R 2016-10-03 14:51:15 -07:00
skein.h OpenZFS 4185 - add new cryptographic checksums to ZFS: SHA-512, Skein, Edon-R 2016-10-03 14:51:15 -07:00
spa.h Fix /etc/hostid on root pool deadlock 2019-09-25 11:27:51 -07:00
spa_boot.h Support custom build directories and move includes 2010-09-08 12:38:56 -07:00
spa_checkpoint.h Serialize ZTHR operations to eliminate races 2019-01-13 10:09:46 -08:00
spa_checksum.h Implementation of AVX2 optimized Fletcher-4 2016-06-02 14:30:51 -07:00
spa_impl.h Fix /etc/hostid on root pool deadlock 2019-09-25 11:27:51 -07:00
space_map.h Introduce auxiliary metaslab histograms 2019-02-20 09:59:56 -08:00
space_reftree.h Illumos #4101, #4102, #4103, #4105, #4106 2014-07-22 09:39:16 -07:00
sysevent.h OpenZFS 6939 - add sysevents to zfs core for commands 2017-07-12 21:28:13 -07:00
trace.h Remove duplicate typedefs from trace.h 2015-01-06 16:53:24 -08:00
trace_acl.h Linux 4.16 compat: inode_set_iversion() 2018-02-08 21:25:19 -08:00
trace_arc.h Support re-prioritizing asynchronous prefetches 2017-12-21 09:13:06 -08:00
trace_common.h OpenZFS 6531 - Provide mechanism to artificially limit disk performance 2016-05-26 10:11:51 -07:00
trace_dbgmsg.h Add line info and SET_ERROR() to ZFS debug log 2017-07-25 23:09:48 -07:00
trace_dbuf.h Prefix all refcount functions with zfs_ 2018-10-01 10:42:05 -07:00
trace_dmu.h tx_waited -> tx_dirty_delayed in trace_dmu.h 2018-01-31 16:13:26 -08:00
trace_dnode.h Fix build-it compilation regression 2017-01-24 08:50:15 -08:00
trace_multilist.h Fix build-it compilation regression 2017-01-24 08:50:15 -08:00
trace_txg.h Fix build-it compilation regression 2017-01-24 08:50:15 -08:00
trace_vdev.h OpenZFS 7614, 9064 - zfs device evacuation/removal 2018-04-14 12:16:17 -07:00
trace_zil.h OpenZFS 8585 - improve batching done in zil_commit() 2017-12-05 09:39:16 -08:00
trace_zio.h Use cstyle -cpP in `make cstyle` check 2016-12-12 10:46:26 -08:00
trace_zrlock.h Fix race in trace point in zrl_add_impl 2018-03-12 11:27:02 -07:00
txg.h Add TRIM support 2019-03-29 09:13:20 -07:00
txg_impl.h OpenZFS 9464 - txg_kick() fails to see that we are quiescing 2018-06-04 14:56:06 -07:00
u8_textprep.h Support custom build directories and move includes 2010-09-08 12:38:56 -07:00
u8_textprep_data.h Support custom build directories and move includes 2010-09-08 12:38:56 -07:00
uberblock.h Multi-modifier protection (MMP) 2017-07-13 13:54:00 -04:00
uberblock_impl.h MMP interval and fail_intervals in uberblock 2019-03-21 12:47:57 -07:00
uio_impl.h deadlock between mm_sem and tx assign in zfs_write() and page fault 2018-10-16 11:11:24 -07:00
unique.h Illumos #3742 2013-11-04 10:55:25 -08:00
uuid.h Support custom build directories and move includes 2010-09-08 12:38:56 -07:00
vdev.h Add TRIM support 2019-03-29 09:13:20 -07:00
vdev_disk.h Add support for autoexpand property 2018-07-23 15:40:15 -07:00
vdev_file.h Use a dedicated taskq for vdev_file 2016-12-21 10:47:15 -08:00
vdev_impl.h Add TRIM support 2019-03-29 09:13:20 -07:00
vdev_indirect_births.h OpenZFS 7614, 9064 - zfs device evacuation/removal 2018-04-14 12:16:17 -07:00
vdev_indirect_mapping.h OpenZFS 7614, 9064 - zfs device evacuation/removal 2018-04-14 12:16:17 -07:00
vdev_initialize.h Add TRIM support 2019-03-29 09:13:20 -07:00
vdev_raidz.h Use cstyle -cpP in `make cstyle` check 2016-12-12 10:46:26 -08:00
vdev_raidz_impl.h Revert raidz_map and _col structure types 2018-01-09 14:46:52 -08:00
vdev_removal.h panic in removal_remap test on 4K devices 2019-09-25 11:27:47 -07:00
vdev_trim.h Add TRIM support 2019-03-29 09:13:20 -07:00
xvattr.h Linux 4.18 compat: inode timespec -> timespec64 2018-06-19 21:51:18 -07:00
zap.h fat zap should prefetch when iterating 2019-09-25 11:27:47 -07:00
zap_impl.h OpenZFS 7793 - ztest fails assertion in dmu_tx_willuse_space 2017-03-07 09:51:59 -08:00
zap_leaf.h Fix ENOSPC in "Handle zap_add() failures in ..." 2018-04-18 14:19:50 -07:00
zcp.h Add tunables for channel programs 2018-06-15 15:10:42 -07:00
zcp_global.h OpenZFS 7431 - ZFS Channel Programs 2018-02-08 15:28:18 -08:00
zcp_iter.h OpenZFS 7431 - ZFS Channel Programs 2018-02-08 15:28:18 -08:00
zcp_prop.h OpenZFS 7431 - ZFS Channel Programs 2018-02-08 15:28:18 -08:00
zfeature.h Revert "zhack: Add 'feature disable' command" 2016-05-17 11:52:07 -07:00
zfs_acl.h Project Quota on ZFS 2018-02-13 14:54:54 -08:00
zfs_context.h Fix lockdep recursive locking false positive in dbuf_destroy 2019-09-25 11:27:49 -07:00
zfs_ctldir.h Rename zfs_sb_t -> zfsvfs_t 2017-03-10 09:51:33 -08:00
zfs_debug.h Add TRIM support 2019-03-29 09:13:20 -07:00
zfs_delay.h Update build system and packaging 2018-05-29 16:00:33 -07:00
zfs_dir.h port async unlinked drain from illumos-nexenta 2019-02-12 10:41:15 -08:00
zfs_fuid.h Update build system and packaging 2018-05-29 16:00:33 -07:00
zfs_ioctl.h Fix send/recv lost spill block 2019-05-07 15:18:44 -07:00
zfs_onexit.h Support custom build directories and move includes 2010-09-08 12:38:56 -07:00
zfs_project.h Project Quota on ZFS 2018-02-13 14:54:54 -08:00
zfs_ratelimit.h Change checksum & IO delay ratelimit values 2018-03-04 17:34:51 -08:00
zfs_rlock.h OpenZFS 9689 - zfs range lock code should not be zpl-specific 2018-10-11 10:19:33 -07:00
zfs_sa.h Project Quota on ZFS 2018-02-13 14:54:54 -08:00
zfs_stat.h Support custom build directories and move includes 2010-09-08 12:38:56 -07:00
zfs_sysfs.h Fix in-kernel sysfs entries 2018-09-06 21:44:52 -07:00
zfs_vfsops.h Fix `zfs set atime|relatime=off|on` behavior on inherited datasets 2019-05-07 10:06:30 -07:00
zfs_vnops.h RHEL 7.5 compat: FMODE_KABI_ITERATE 2018-05-02 15:01:24 -07:00
zfs_znode.h Fix deadlock in 'zfs rollback' 2019-09-25 11:27:50 -07:00
zil.h make zil max block size tunable 2020-01-22 13:48:56 -08:00
zil_impl.h make zil max block size tunable 2020-01-22 13:48:56 -08:00
zio.h Add TRIM support 2019-03-29 09:13:20 -07:00
zio_checksum.h Remove dependency on linear ABD 2017-03-29 12:24:51 -07:00
zio_compress.h lz4_decompress_abd declared but not defined 2019-09-25 11:27:47 -07:00
zio_crypt.h Add support for decryption faults in zinject 2018-05-02 15:36:20 -07:00
zio_impl.h Add TRIM support 2019-03-29 09:13:20 -07:00
zio_priority.h Add TRIM support 2019-03-29 09:13:20 -07:00
zpl.h Linux 4.18 compat: inode timespec -> timespec64 2018-06-19 21:51:18 -07:00
zrlock.h OpenZFS 6328 - Fix cstyle errors in zfs codebase 2017-01-12 09:42:11 -08:00
zthr.h Serialize ZTHR operations to eliminate races 2019-01-13 10:09:46 -08:00
zvol.h Add port of FreeBSD 'volmode' property 2017-07-12 13:05:37 -07:00