On 6/21/2015 2:23 PM, Tom Metro wrote:
That doesn't entirely make sense. If setting swappiness to zero means swap is never used, and setting it to a high value means it is aggressively used, then in the latter case it means the kernel is moving stuff from RAM to swap. If it is moved to swap, it ought to free up physical RAM.
swappiness does not prevent the kernel from swapping. It controls how aggressive the kernel is in writing out least-used pages to disk or other non-volatile storage.
When set to 0 the kernel will not write pages to disk until all physical RAM is allocated. Then it will start writing out pages normally. The higher the setting, the more aggressive the kernel will be in writing out least-used pages.
Clean pages (allocated pages that have been written to disk) remain in the page cache in case they are needed. swappiness = 100 does not mean that every page gets read from disk every time it is accessed. Pages are dropped from the page cache when their processes release the allocations or processes try to allocate more RAM. The kernel drops least-used clean pages from the page cache to meet the allocation request. swappiness has no effect on the page cache.
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.
-- Rich P. _______________________________________________ Discuss mailing list Discuss@blu.org http://lists.blu.org/mailman/listinfo/discuss
