From: Cao Guanghui <[email protected]> The maximum number of concurrent background work items (promotions, demotions, writebacks) in the SMQ policy was hardcoded to 4096, with a FIXME comment noting it should be made configurable.
This value was originally tuned down from 10240 to balance memory overhead (~128 bytes per entry, ~512KB at 4096 entries) against I/O parallelism. However, different workloads and cache sizes may benefit from different limits: - Write-heavy workloads may need more writeback concurrency - Very large caches (10+ TB) may need more promotion slots - Memory-constrained systems may want a lower limit Make this configurable via the module parameter "smq_max_background_work" (defaulting to 4096 to preserve existing behaviour). Clamp the value to at least 1 to prevent setting 0, which would block all background work. The parameter only affects newly created cache devices; existing caches retain their value from creation time. Signed-off-by: Cao Guanghui <[email protected]> --- drivers/md/dm-cache-policy-smq.c | 12 +++++++++++- 1 file changed, 11 insertions(+), 1 deletion(-) diff --git a/drivers/md/dm-cache-policy-smq.c b/drivers/md/dm-cache-policy-smq.c index dd77a93fd68d..646f7c8936ad 100644 --- a/drivers/md/dm-cache-policy-smq.c +++ b/drivers/md/dm-cache-policy-smq.c @@ -21,6 +21,16 @@ /*----------------------------------------------------------------*/ +/* + * Maximum number of concurrent background work items (promotions, + * demotions, writebacks) that can be queued in the background tracker. + * Tuneable via the module parameter smq_max_background_work. + * Only affects newly created cache devices. + */ +static unsigned int smq_max_background_work = 4096; +module_param(smq_max_background_work, uint, 0644); +MODULE_PARM_DESC(smq_max_background_work, "Max concurrent background work items"); + /* * Safe division functions that return zero on divide by zero. */ @@ -1816,7 +1826,7 @@ __smq_create(dm_cblock_t cache_size, sector_t origin_size, sector_t cache_block_ mq->next_hotspot_period = jiffies; mq->next_cache_period = jiffies; - mq->bg_work = btracker_create(4096); /* FIXME: hard coded value */ + mq->bg_work = btracker_create(max(1u, smq_max_background_work)); if (!mq->bg_work) goto bad_btracker; -- 2.25.1
