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authorJoe Thornber <ejt@redhat.com>2013-12-09 12:53:05 +0000
committerMike Snitzer <snitzer@redhat.com>2014-01-07 10:14:33 -0500
commit78e03d69733c48312ae81fe4ac0790dbea412b9d (patch)
tree47ffaceb2c4c977ab639810d6812a356f364def4 /Documentation/device-mapper
parentb815805154cc62debbc423a6c27ae39290b300ae (diff)
downloadlinux-78e03d69733c48312ae81fe4ac0790dbea412b9d.tar.bz2
dm cache policy mq: introduce three promotion threshold tunables
Internally the mq policy maintains a promotion threshold variable. If the hit count of a block not in the cache goes above this threshold it gets promoted to the cache. This patch introduces three new tunables that allow you to tweak the promotion threshold by adding a small value. These adjustments depend on the io type: read_promote_adjustment: READ io, default 4 write_promote_adjustment: WRITE io, default 8 discard_promote_adjustment: READ/WRITE io to a discarded block, default 1 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. Signed-off-by: Joe Thornber <ejt@redhat.com> Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Diffstat (limited to 'Documentation/device-mapper')
-rw-r--r--Documentation/device-mapper/cache-policies.txt16
1 files changed, 14 insertions, 2 deletions
diff --git a/Documentation/device-mapper/cache-policies.txt b/Documentation/device-mapper/cache-policies.txt
index df52a849957f..66c2774c0c64 100644
--- a/Documentation/device-mapper/cache-policies.txt
+++ b/Documentation/device-mapper/cache-policies.txt
@@ -40,8 +40,11 @@ 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>' and
- 'random_threshold <#nr_random_ios>'.
+ '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. The random threshold
@@ -55,6 +58,15 @@ since spindles tend to have good bandwidth. The io_tracker counts
contiguous I/Os to try to spot when the io is in one of these sequential
modes.
+Internally the mq policy maintains a promotion threshold variable. 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.
+
cleaner
-------