On Thu, Aug 19, 2010 at 07:33:57PM +0900, Minchan Kim wrote: > 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. And if the exit path for the OOM kill needs to allocate a page what should it do? > 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. :) > -- Mel Gorman Part-time Phd Student Linux Technology Center University of Limerick IBM Dublin Software Lab -- 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=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>