From: Matthew Wilcox <willy@xxxxxxxxxxxxx> Date: Wed, 10 May 2017 10:17:03 -0700 > On Wed, May 10, 2017 at 11:19:43AM -0400, David Miller wrote: >> From: Michal Hocko <mhocko@xxxxxxxxxx> >> Date: Wed, 10 May 2017 16:57:26 +0200 >> >> > Have you measured that? I do not think it would be super hard to >> > measure. I would be quite surprised if this added much if anything at >> > all as the whole struct page should be in the cache line already. We do >> > set reference count and other struct members. Almost nobody should be >> > looking at our page at this time and stealing the cache line. On the >> > other hand a large memcpy will basically wipe everything away from the >> > cpu cache. Or am I missing something? >> >> I guess it might be clearer if you understand what the block >> initializing stores do on sparc64. There are no memory accesses at >> all. >> >> The cpu just zeros out the cache line, that's it. >> >> No L3 cache line is allocated. So this "wipe everything" behavior >> will not happen in the L3. > > There's either something wrong with your explanation or my reading > skills :-) > > "There are no memory accesses" > "No L3 cache line is allocated" > > You can have one or the other ... either the CPU sends a cacheline-sized > write of zeroes to memory without allocating an L3 cache line (maybe > using the store buffer?), or the CPU allocates an L3 cache line and sets > its contents to zeroes, probably putting it in the last way of the set > so it's the first thing to be evicted if not touched. There is no conflict in what I said. Only an L2 cache line is allocated and cleared. L3 is left alone. -- 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>
