On Wed, 2011-12-14 at 01:44 +0800, Mike Waychison wrote: > On a single core system with kernel preemption disabled, it is possible > for the memory system to be so taxed that kswapd cannot make any forward > progress. This can happen when most of system memory is tied up as > anonymous memory without swap enabled, causing kswapd to consistently > fail to achieve its watermark goals. In turn, sleeping_prematurely() > will consistently return true and kswapd_try_to_sleep() to never invoke > schedule(). This causes the kswapd thread to stay on the CPU in > perpetuity and keeps other threads from processing oom-kills to reclaim > memory. > > The cond_resched() instance in balance_pgdat() is never called as the > loop that iterates from DEF_PRIORITY down to 0 will always set > all_zones_ok to true, and not set it to false once we've passed > DEF_PRIORITY as zones that are marked ->all_unreclaimable are not > considered in the "all_zones_ok" evaluation. > > This change modifies kswapd_try_to_sleep to ensure that we enter > scheduler at least once per invocation if needed. This allows kswapd to > get off the CPU and allows other threads to die off from the OOM killer > (freeing memory that is otherwise unavailable in the process). your description suggests zones with all_unreclaimable set. but in this case sleeping_prematurely() will return false instead of true, kswapd will do sleep then. is there anything I missed? -- 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>