On 3/5/2012 4:56 PM, Johannes Weiner wrote: > On Fri, Mar 02, 2012 at 12:36:40PM -0500, Satoru Moriya wrote: >> Sometimes we'd like to avoid swapping out anonymous memory >> in particular, avoid swapping out pages of important process or >> process groups while there is a reasonable amount of pagecache >> on RAM so that we can satisfy our customers' requirements. >> >> OTOH, we can control how aggressive the kernel will swap memory pages >> with /proc/sys/vm/swappiness for global and >> /sys/fs/cgroup/memory/memory.swappiness for each memcg. >> >> But with current reclaim implementation, the kernel may swap out >> even if we set swappiness==0 and there is pagecache on RAM. >> >> This patch changes the behavior with swappiness==0. If we set >> swappiness==0, the kernel does not swap out completely >> (for global reclaim until the amount of free pages and filebacked >> pages in a zone has been reduced to something very very small >> (nr_free + nr_filebacked < high watermark)). >> >> Any comments are welcome. > > Last time I tried that (getting rid of sc->may_swap, using > !swappiness), it was rejected it as there were users who relied on > swapping very slowly with this setting. > > KOSAKI-san, do I remember correctly? Do you still think it's an > issue? > > Personally, I still think it's illogical that !swappiness allows > swapping and would love to see this patch go in. Thank you. I brought back to memory it. Unfortunately DB folks are still mainly using RHEL5 generation distros. At that time, swapiness=0 doesn't mean disabling swap. They want, "don't swap as far as kernel has any file cache page". but linux don't have such feature. then they used swappiness for emulate it. So, I think this patch clearly make userland harm. Because of, we don't have an alternative way. -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>