3 ms·
It seems to me that if you hit the point where you really need swap, then you're already in trouble. Maybe that swap gives you a little buffer before things ge
by blunte 7y ago
It seems to me that if you hit the point where you really need swap, then you're already in trouble. Maybe that swap gives you a little buffer before things get really bad, but chances are that will just keep you unaware of your impending problem until they go critical (unless you have lots of good monitoring/alerting).
- azernik 7y agoYou would think so, but as Rachel points out the Linux kernel displays some pathological behavior with noswap that even a tiny amount of swap lets it get around. Something weird is going on in the memory management code.
- VectorLock 7y agoI'm not sure what shes observing other than "feels weird" but my observation is the exact opposite, but my observations usually have some measurements to them.
- aardvarklegend 7y agoIt requires a perfect storm of just shy of 100% used memory and a lot of mmaped io. In that case the mmaped can get shunted to a handful of pages (or even one page) and so you lose all ability to have any block io larger then one page size. And every page of memory involves a fully blocking io request. It’s most certainly real for certain workloads (databases are common).
- azernik 7y ago"Feels weird" when she logs on to investigate serious performance problems that she's getting paged for.