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45305a067f
arc_evict_hdr() returns number of evicted bytes in scope of specific state. For ghost states it does not mean the amount of really freed memory, but the logical buffer size. It is correct for the eviction process, but not for waking up threads waiting for ARC size reduction, as added in "Revise ARC shrinker algorithm" commit, causing premature wakeups while ARC is still overflowed, allowing even bigger overflow, plus processing overhead when next allocation will also get blocked, probably also for too short time. To fix that make arc_evict_hdr() also return the amount of really freed memory, which for the ghost states is only the header, and use it to update arc_evict_count instead. Originally I was thinking to not return it at all, since arc_get_data_impl() does not account for the headers, but decided that some slow allocation progress is better than long waits, reaching on my tests up to 100ms. To reduce negative latency effects of long time periods when reclaim thread can free little real memory, start reclamation process earlier, before we actually reached the overflow threshold, when we have to throttle new allocations. We can also do it without taking global arc_evict_lock, reducing the contention. Reviewed-by: George Wilson <gwilson@delphix.com> Reviewed-by: Allan Jude <allan@klarasystems.com> Reviewed-by: Ryan Moeller <ryan@iXsystems.com> Signed-off-by: Alexander Motin <mav@FreeBSD.org> Closes #12279 |
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