On Sun, Jun 21, 2015 at 03:39:46PM -0400, Richard Pieri wrote: > When a process tries to allocate more pages than the total of clean > and unallocated pages in the page cache, well, that's an overload. > Overloaded system is overloaded. Game over. Install more RAM or > don't overload the system. If neither option is viable then put your > page file or partition on a fast SSD. That won't solve the problem > but it will make it seem less severe.
Remember that a lot of our expectations around VM and swapping come from a time when a multiuser system might have 16 MB of RAM. Hard disks transferred 25MB/s. Suppose you had a 16MB system and allocated 16MB of disk for swap. A request to evict a 4MB process and pull in another one would take about 350ms -- not too bad. Now let's say you have a 16GB system with 16GB of swap on disk, and you want to evict a 4GB browser process and pull in another one. Disk speeds went up to 100MB/s, so it only takes 80 seconds or so! With a consumer SSD that gets lucky, you have a 500MB/s transfer rate and can do it in 16 seconds, practically no time at all. It's certainly less severe, but it isn't much fun. Conclusion: swap is a last-ditch mechanism to save your system from having to kill processes. The other two uses -- Linux trades out pages that are likely to never be called again, or uses the swap space as a sleep-time mechanism to store memory -- are still viable. It would probably be best for a desktop machine that *is* going to be put to sleep overnight to have a minimal amount of swap, and mount a larger, pre-prepared swapspace for the purpose of sleeping. Unmount it when awake. -dsr- _______________________________________________ Discuss mailing list [email protected] http://lists.blu.org/mailman/listinfo/discuss
