On Thu, 19 Aug 2010, Chris Webb wrote: > I tried this on a handful of the problem hosts before re-adding their swap. > One of them now runs without dipping into swap. The other three I tried had > the same behaviour of sitting at zero swap usage for a while, before > suddenly spiralling up with %wait going through the roof. I had to swapoff > on them to bring them back into a sane state. So it looks like it helps a > bit, but doesn't cure the problem. > > I could definitely believe an explanation that we're swapping in preference > to allocating remote zone pages somehow, given the imbalance in free memory > between the nodes which we saw. However, I read the documentation for > vm.zone_reclaim_mode, which suggests to me that when it was set to zero, > pages from remote zones should be allocated automatically in preference to > swap given that zone_reclaim_mode & 4 == 0? If zone reclaim is off then pages from other nodes will be allocated if a node is filled up with page cache. zone reclaim typically only evicts clean page cache pages in order to keep the additional overhead down. Enabling swapping allows a more aggressive form of recovering memory in preference of going off line. The VM should work fine even without zone reclaim. -- 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>