Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> writes: > On Sat, Jul 30, 2011 at 8:27 AM, Linus Torvalds > <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote: >> >> Do we allocate the page map array sufficiently aligned that we >> actually don't ever have the case of straddling a cacheline? I didn't >> check. > > Oh, and another thing worth checking: did somebody actually check the > timings for: I would like to see a followon patch that moves the mem_cgroup pointer back into struct page. Copying some mem_cgroup people. > > - *just* the alignment change? > > IOW, maybe some of the netperf improvement isn't from the lockless > path, but exactly from 'struct page' always being in a single > cacheline? > > - check performance with cmpxchg16b *without* the alignment. > > Sometimes especially intel is so good at unaligned accesses that > you wouldn't see an issue. Now, locked ops are usually special (and As Eric pointed out CMPXCHG16B requires alignment, it #GPs otherwise. -Andi -- ak@xxxxxxxxxxxxxxx -- Speaking for myself only -- 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>