On Mon, Oct 01, 2012 at 08:15:19PM +0300, Kirill A. Shutemov wrote: > I think performance is not the first thing we should look at. We need to > choose which implementation is easier to support. Having to introduce a special pmd bitflag requiring architectural support is actually making it less self contained. The zero page support is made optional of course, but the physical zero page would have worked without the arch noticing. > Applications which benefit from zero page are quite rare. We need to > provide a huge zero page to avoid huge memory consumption with THP. > That's it. Performance optimization for that rare case is overkill. I still don't like the idea of some rare app potentially running significantly slower (and we may not be notified because it's not a breakage, if they're simulations it's hard to tell it's slower because of different input or because of zero page being introduced). If we knew for sure that zero pages accesses were always rare I wouldn't care of course. But rare app != rare access. The physical zero page patchset is certainly bigger, but it was mostly localized in huge_memory.c so I don't see it at very intrusive even if bigger. Anyway if others sees the virtual zero page as easier to maintain, I'm fine either ways. -- 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/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>