On Tue, 18 Oct 2011, Andi Kleen wrote: > Hugh Dickins <hughd@xxxxxxxxxx> writes: > > > A process spent 30 minutes exiting, just munlocking the pages of a large > > anonymous area that had been alternately mprotected into page-sized vmas: > > for every single page there's an anon_vma walk through all the other > > little vmas to find the right one. > > We had the same problem recently after a mmap+touch workload: in this > case it was hugepaged walking all these anon_vmas and the list was over > 100k long. > > Had some data on this at plumbers: > http://halobates.de/plumbers-fork-locks_v2.pdf > > > A general fix to that would be a lot more complicated (use prio_tree on > > anon_vma?), but there's one very simple thing we can do to speed up the > > common case: if a page to be munlocked is mapped only once, then it is > > our vma that it is mapped into, and there's no need whatever to walk > > through all the others. > > I think we need a generic fix, this problem does not only happen > in munmap. Thanks for the pointer, Andi, I'll have to look into it when I've a moment; but I don't look forward to making this area more complicated. Hugh -- 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>