On Mon, 2014-02-24 at 17:42 -0800, Linus Torvalds wrote: > On Mon, Feb 24, 2014 at 5:16 PM, Davidlohr Bueso <davidlohr@xxxxxx> wrote: > > > > If we add the two missing bits to the shifting and use PAGE_SHIFT (x86 > > at least) we get just as good results as with 10. So we would probably > > prefer hashing based on the page number and not some offset within the > > page. > > So just > > int idx = (addr >> PAGE_SHIFT) & 3; > > works fine? Yep. > > That makes me think it all just wants to be maximally spread out to > approximate some NRU when adding an entry. > > Also, as far as I can tell, "vmacache_update()" should then become > just a simple unconditional > > int idx = (addr >> PAGE_SHIFT) & 3; > current->vmacache[idx] = newvma; > Yes, my thoughts exactly! > because your original code did > > + if (curr->vmacache[idx] != newvma) > + curr->vmacache[idx] = newvma; > > and that doesn't seem to make sense, since if "newvma" was already in > the cache, then we would have found it when looking up, and we > wouldn't be here updating it after doing the rb-walk? I noticed this as well but kept my fingers shut and was planning on fixing it in v2. > And with the > per-mm cache removed, all that should remain is that simple version, > no? Yes. Although I am planning on keeping the current way of doing things for nommu configs as there's no dup_mmap. I'm not sure if that's the best idea though, it makes things less straightforward. > You don't even need the "check the vmcache sequence number and > clear if bogus", because the rule should be that you have always done > a "vmcache_find()" first, which should have done that.. Makes sense, noted. Thanks, Davidlohr -- 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>