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Diffstat (limited to 'Documentation/device-mapper/cache-policies.txt')
| -rw-r--r-- | Documentation/device-mapper/cache-policies.txt | 16 |
1 files changed, 14 insertions, 2 deletions
diff --git a/Documentation/device-mapper/cache-policies.txt b/Documentation/device-mapper/cache-policies.txt index df52a849957..66c2774c0c6 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 ------- |