4 ms·
Could this be a reflection of the increasing gulf between RAM speed and HD speed? Even with NVMe drives, which one probably shouldn't be swapping to anyway, RAM
by rootbear 10y ago
Could this be a reflection of the increasing gulf between RAM speed and HD speed? Even with NVMe drives, which one probably shouldn't be swapping to anyway, RAM is orders of magnitude faster.
- Retric 10y agoWith SSD's disk is not that slow.
- SapphireSun 10y agoSSDs are only ~4x faster than magnetic last I checked. If RAM is 100ns per access, and hd access is down from say, 1ms to 0.25ms, that's still a huge huge gap. 4x isn't even an order of magnitude. EDIT: see comment below for more accurate numbers.
- snowwindwaves 10y agoFrom the article: >A typical reference to RAM is in the area of 100ns, accessing data on a SSD 150μs (so 1500 times of the RAM) and accessing data on a rotating disk 10ms (so 100.000 times the RAM.
- SapphireSun 10y agoThank you for the correction. I should have read more carefully. Still, we're talking 3 orders of magnitude for SSD vs RAM.
- xinyhn 10y agoreminded me of this... Latency Numbers Every Programmer Should Know https://gist.github.com/jboner/2841832 https://gist.github.com/jboner/2841832
- curlypaul924 10y agoI think, among other things, it has to do with the size of the swap space relative to the speed of the swap device. IME high disk i/o combined with large swap space means swap never fills up and the OOM killer doesn't kick in. On systems with less RAM and swap, OOM conditions were hit much sooner, even with slower disks. Default settings for dirty ratio and dirty background ratio exacerbate the issue: more data is held onto before it is written, and once the background ratio is hit, any application writing to disk will block.