In <201102131521.18065....@iguanasuicide.net>, Boyd Stephen Smith Jr. wrote: >Both types of memory are effectively free. Cache can be dropped >willy-nilly. Buffers can be reclaimed by waiting for their I/O to complete. > Both of these actions are done automatically by the kernel when >application memory pressure increases.
The choice to drop caches, wait on buffers, or swap out application memory is controlled by /proc/sys/vm/swappiness. A value of 100 means "always" swap out application memory. A value of 0 means "always" wait on buffers or drop caches. I use a value of 1, the default is 60. There was at one point a patch to let the kernel auto-tune this value based on current memory usage, but I don't know if it ever got mainlined, or if it gave measurable gains. Since the cost of the "wrong" decision is mostly the same (read a page from swap or read a page from disk) it would seem, IMVHO, that it is more important to swap/drop the LRU/LFU page independent of whether that is applications memory or cache/buffers. -- Boyd Stephen Smith Jr. ,= ,-_-. =. b...@iguanasuicide.net ((_/)o o(\_)) ICQ: 514984 YM/AIM: DaTwinkDaddy `-'(. .)`-' http://iguanasuicide.net/ \_/
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