Hello Johannes, On Mon, Jul 25, 2011 at 10:38:41PM +0200, Johannes Weiner wrote: > With defrag mode enabled per default, huge page allocations pass > __GFP_WAIT and may drop compaction into sync-mode where they wait for > pages under writeback. > > I observe applications hang for several minutes(!) when they fault in > huge pages and compaction starts to wait on in-"flight" USB stick IO. > > This patch disables defrag mode for page fault allocations unless the > VMA is madvised explicitely. Khugepaged will continue to allocate > with __GFP_WAIT per default, but stalls are not a problem of > application responsiveness there. Allocating memory without __GFP_WAIT means THP it's like disabled except when there's plenty of memory free after boot, even trying with __GFP_WAIT and without compaction would be better than that. We don't want to modify all apps, just a few special ones should have the madvise like qemu-kvm for example (for embedded in case there's embedded virt). If you want to make compaction and migrate run without ever dropping into sync-mode (or aborting if we've to wait on too many pages) I think it'd be a whole lot better. If you could show the SYSRQ+T during the minute wait it'd be interesting too. There was also some compaction bug that would lead to minutes of stall in congestion_wait, those are fixed in current kernels. -- 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>