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authorLinus Torvalds <torvalds@linux-foundation.org>2016-03-16 17:26:37 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2016-03-16 17:26:37 -0700
commit6968e6f8329d014920331dd2cf166ccd474b5299 (patch)
treea92c813c2f24b26c0eb6c294e1dc3d8d402211cc /Documentation
parentcae8da047b165aaf334fd87020c2ea7ee020c41c (diff)
parent98dbc9c6c61698792e3a66f32f3bf066201d42d7 (diff)
Merge tag 'dm-4.6-changes' of git://git.kernel.org/pub/scm/linux/kernel/git/device-mapper/linux-dm
Pull device mapper updates from Mike Snitzer: - Most attention this cycle went to optimizing blk-mq request-based DM (dm-mq) that is used exclussively by DM multipath: - A stable fix for dm-mq that eliminates excessive context switching offers the biggest performance improvement (for both IOPs and throughput). - But more work is needed, during the next cycle, to reduce spinlock contention in DM multipath on large NUMA systems. - A stable fix for a NULL pointer seen when DM stats is enabled on a DM multipath device that must requeue an IO due to path failure. - A stable fix for DM snapshot to disallow the COW and origin devices from being identical. This amounts to graceful failure in the face of userspace error because these devices shouldn't ever be identical. - Stable fixes for DM cache and DM thin provisioning to address crashes seen if/when their respective metadata device experiences failures that cause the transition to 'fail_io' mode. - The DM cache 'mq' policy is now an alias for the 'smq' policy. The 'smq' policy proved to be consistently better than 'mq'. As such 'mq', with all its complex user-facing tunables, has been eliminated. - Improve DM thin provisioning to consistently return -ENOSPC once the thin-pool's data volume is out of space. - Improve DM core to properly handle error propagation if bio_integrity_clone() fails in clone_bio(). - Other small cleanups and improvements to DM core. * tag 'dm-4.6-changes' of git://git.kernel.org/pub/scm/linux/kernel/git/device-mapper/linux-dm: (41 commits) dm: fix rq_end_stats() NULL pointer in dm_requeue_original_request() dm thin: consistently return -ENOSPC if pool has run out of data space dm cache: bump the target version dm cache: make sure every metadata function checks fail_io dm: add missing newline between DM_DEBUG_BLOCK_STACK_TRACING and DM_BUFIO dm cache policy smq: clarify that mq registration failure was for 'mq' dm: return error if bio_integrity_clone() fails in clone_bio() dm thin metadata: don't issue prefetches if a transaction abort has failed dm snapshot: disallow the COW and origin devices from being identical dm cache: make the 'mq' policy an alias for 'smq' dm: drop unnecessary assignment of md->queue dm: reorder 'struct mapped_device' members to fix alignment and holes dm: remove dummy definition of 'struct dm_table' dm: add 'dm_numa_node' module parameter dm thin metadata: remove needless newline from subtree_dec() DMERR message dm mpath: cleanup reinstate_path() et al based on code review dm mpath: remove __pgpath_busy forward declaration, rename to pgpath_busy dm mpath: switch from 'unsigned' to 'bool' for flags where appropriate dm round robin: use percpu 'repeat_count' and 'current_path' dm path selector: remove 'repeat_count' return from .select_path hook ...
Diffstat (limited to 'Documentation')
-rw-r--r--Documentation/device-mapper/cache-policies.txt39
1 files changed, 2 insertions, 37 deletions
diff --git a/Documentation/device-mapper/cache-policies.txt b/Documentation/device-mapper/cache-policies.txt
index d9246a32e673..e5062ad18717 100644
--- a/Documentation/device-mapper/cache-policies.txt
+++ b/Documentation/device-mapper/cache-policies.txt
@@ -28,51 +28,16 @@ Overview of supplied cache replacement policies
multiqueue (mq)
---------------
-This policy has been deprecated in favor of the smq policy (see below).
+This policy is now an alias for smq (see below).
-The multiqueue policy has three sets of 16 queues: one set for entries
-waiting for the cache and another two for those in the cache (a set for
-clean entries and a set for dirty entries).
+The following tunables are accepted, but have no effect:
-Cache entries in the queues are aged based on logical time. Entry into
-the cache is based on variable thresholds and queue selection is based
-on hit count on entry. The policy aims to take different cache miss
-costs into account and to adjust to varying load patterns automatically.
-
-Message and constructor argument pairs are:
'sequential_threshold <#nr_sequential_ios>'
'random_threshold <#nr_random_ios>'
'read_promote_adjustment <value>'
'write_promote_adjustment <value>'
'discard_promote_adjustment <value>'
-The sequential threshold indicates the number of contiguous I/Os
-required before a stream is treated as sequential. Once a stream is
-considered sequential it will bypass the cache. The random threshold
-is the number of intervening non-contiguous I/Os that must be seen
-before the stream is treated as random again.
-
-The sequential and random thresholds default to 512 and 4 respectively.
-
-Large, sequential I/Os are probably better left on the origin device
-since spindles tend to have good sequential I/O bandwidth. The
-io_tracker counts contiguous I/Os to try to spot when the I/O is in one
-of these sequential modes. But there are use-cases for wanting to
-promote sequential blocks to the cache (e.g. fast application startup).
-If sequential threshold is set to 0 the sequential I/O detection is
-disabled and sequential I/O will no longer implicitly bypass the cache.
-Setting the random threshold to 0 does _not_ disable the random I/O
-stream detection.
-
-Internally the mq policy determines a promotion threshold. If the hit
-count of a block not in the cache goes above this threshold it gets
-promoted to the cache. The read, write and discard promote adjustment
-tunables allow you to tweak the promotion threshold by adding a small
-value based on the io type. They default to 4, 8 and 1 respectively.
-If you're trying to quickly warm a new cache device you may wish to
-reduce these to encourage promotion. Remember to switch them back to
-their defaults after the cache fills though.
-
Stochastic multiqueue (smq)
---------------------------