On Thu, Aug 19, 2010 at 5:06 PM, Mel Gorman <mel@xxxxxxxxx> wrote: > On Wed, Aug 18, 2010 at 11:57:26PM +0900, Minchan Kim wrote: >> On Wed, Aug 18, 2010 at 09:51:23AM +0100, Mel Gorman wrote: >> > > What's a window low and min wmark? Maybe I can miss your point. >> > > >> > >> > The window is due to the fact kswapd is not awake yet. The window is because >> > kswapd might not be awake as NR_FREE_PAGES is higher than it should be. The >> > system is really somewhere between the low and min watermark but we are not >> > taking the accurate measure until kswapd gets woken up. The first allocation >> > to notice we are below the low watermark (be it due to vmstat refreshing or >> > that NR_FREE_PAGES happens to report we are below the watermark regardless of >> > any drift) wakes kswapd and other callers then take an accurate count hence >> > "we could breach the watermark but I'm expecting it can only happen for at >> > worst one allocation". >> >> Right. I misunderstood your word. >> One more question. >> >> Could you explain live lock scenario? >> > > Lets say > > NR_FREE_PAGES = 256 > Actual free pages = 8 > > The PCP lists get refilled in patch taking all 8 pages. Now there are > zero free pages. Reclaim kicks in but to reclaim any pages it needs to > clean something but all the pages are on a network-backed filesystem. To > clean them, it must transmit on the network so it tries to allocate some > buffers. > > The livelock is that to free some memory, an allocation must succeed but > for an allocation to succeed, some memory must be freed. The system Yes. I understood this as livelock but at last VM will kill victim process then it can allocate free pages. So I think it's not a livelock. > might still remain alive if a process exits and does not need to > allocate memory while exiting but by and large, the system is in a > dangerous state. Do you mean dangerous state of the system is livelock? Maybe not. I can't understand livelock in this context. Anyway, I am okay with this patch except livelock pharse. :) Thanks, Mel. -- Kind regards, Minchan Kim -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxxx For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href