4 ms·
>On SSDs, swapping out anonymous pages and reclaiming file pages are essentially equivalent in terms of performance/latency... >we simply transfer the disk I/O
by yyyk 5y ago
>On SSDs, swapping out anonymous pages and reclaiming file pages are essentially equivalent in terms of performance/latency...
>we simply transfer the disk I/O of swapping to dropping hot page caches and dropping code segments we need soon
That's a key argument, but it ignores that swap changes a read I/O to a write I/O - on HDD write is much slower (this is acknowledged in the article), and SSD have a write limit (this is not ack'd).
I know all SSD manufacturers these days say their limit is high, but I'm still a bit leery.
- schmorptron 5y agoAren't the write limits on ssd going to be lower again with mlc?
- yyyk 5y agoI think we're at tlc and qlc for common SSD drives now? And soon enough plc? Manufacturers always say the write limits are very high despite using less durable tech, and I am not sure I believe them.
- zajio1am 5y agoThere is also issue that SSD write is much slower than even HDD write once internal buffers are saturated, and has unpleasant consequences. When my system got thrashing (droping hot pages) due to memory pressure in a limited cgroup, i see continuous 400MB/s disk read traffic (as pages are read and then dropped), but the rest of system (outside the cgroup) is usable. But when i do some big file copying, the SSD sometimes causes multi-second system freeze due to locked SSD I/O. Also, the write limits are pretty tight. Recently, i replaced my SSD after just 6 years of light use, because it reported average sector overwrite rate to be ~3300 of 3000 nominal lifetime. And current TLD and QLD SSDs have these limits even smaller.