On 08/16/2012 12:40 PM, Andrea Arcangeli wrote: > Hi Andrew, > > On Thu, Aug 16, 2012 at 12:20:23PM -0700, Andrew Morton wrote: >> That's a pretty big improvement for a rather fake test case. I wonder >> how much benefit we'd see with real workloads? > > The same discussion happened about the zero page in general and > there's no easy answer. I seem to recall that it was dropped at some > point and then we reintroduced the zero page later. > > Most of the time it won't be worth it, it's just a few pathological > compute loads that benefits IIRC. So I'm overall positive about it > (after it's stable). > > Because this is done the right way (i.e. to allocate an hugepage at > the first wp fault, and to fallback exclusively if compaction fails) > it will help much less than the 4k zero pages if the zero pages are > scattered over the address space and not contiguous (it only helps if > there are 512 of them in a row). OTOH if they're contiguous, the huge > zero pages will perform better than the 4k zero pages. > One thing that I asked for testing a "virtual zero page" where the same page (or N pages for N-way page coloring) is reused across a page table. It would have worse TLB performance but likely *much* better cache behavior. -hpa -- 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>