Change Details

When estimating working set size, measure only allocation batches, not free batches. Allocation and free patterns can be very different. For example, ZFS on vm_lowmem event can free to UMA few gigabytes of memory in one call, but it does not mean it will request the same amount back that fast too, in fact it won't. Update working set size on every reclamation call, shrinking caches fast(er) under pressure. Lack of this caused repeating vm_lowmem events squeezing more and more memory out of real consumers only to make it stuck in UMA caches. I saw ZFS drop ARC size in half before previous algorithm after periodic WSS update decided to reclaim UMA caches. Introduce voluntary reclamation of UMA caches not used for a long time. For each zdom track longterm minimal cache size watermark, freeing ~30% of unused items every 30 minutes. Freed memory can get better use by other consumers. For example, ZFS won't grow its ARC unless it see free memory, since it does not know it is not really used. And even if memory is not really needed, periodic free during inactivity periods should reduce its fragmentation.

When estimating working set size, measure only allocation batches, not free batches. Allocation and free patterns can be very different. For example, ZFS on vm_lowmem event can free to UMA few gigabytes of memory in one call, but it does not mean it will request the same amount back that fast too, in fact it won't. Update working set size on every reclamation call, shrinking caches fast(er) under pressure. Lack of this caused repeating vm_lowmem events squeezing more and more memory out of real consumers only to make it stuck in UMA caches. I saw ZFS drop ARC size in half before previous algorithm after periodic WSS update decided to reclaim UMA caches. Introduce voluntary reclamation of UMA caches not used for a long time. For each zdom track longterm minimal cache size watermark, freeing some unused items every UMA_TIMEOUT after first 15 minutes without cache misses. Freed memory can get better use by other consumers. For example, ZFS won't grow its ARC unless it see free memory, since it does not know it is not really used. And even if memory is not really needed, periodic free during inactivity periods should reduce its fragmentation.

When estimating working set size, measure only allocation batches, not free batches. Allocation and free patterns can be very different. For example, ZFS on vm_lowmem event can free to UMA few gigabytes of memory in one call, but it does not mean it will request the same amount back that fast too, in fact it won't. Update working set size on every reclamation call, shrinking caches fast(er) under pressure. Lack of this caused repeating vm_lowmem events squeezing more and more memory out of real consumers only to make it stuck in UMA caches. I saw ZFS drop ARC size in half before previous algorithm after periodic WSS update decided to reclaim UMA caches. Introduce voluntary reclamation of UMA caches not used for a long time. For each zdom track longterm minimal cache size watermark, freeing ~30% ofsome unused items every 30UMA_TIMEOUT after first 15 minutesutes without cache misses. Freed memory can get better use by other consumers. For example, ZFS won't grow its ARC unless it see free memory, since it does not know it is not really used. And even if memory is not really needed, periodic free during inactivity periods should reduce its fragmentation.