On Wed 22-02-17 18:51:31, Wei Yang wrote: > On Wed, Feb 22, 2017 at 09:49:47AM +0100, Michal Hocko wrote: > >On Thu 09-02-17 21:59:29, Wei Yang wrote: > >> On Tue, Feb 07, 2017 at 04:41:21PM +0100, Michal Hocko wrote: > >> >On Tue 07-02-17 23:32:47, Wei Yang wrote: > >> >> On Tue, Feb 07, 2017 at 10:45:57AM +0100, Michal Hocko wrote: > >> >[...] > >> >> >Is there any reason why for_each_mem_pfn_range cannot be changed to > >> >> >honor the given start/end pfns instead? I can imagine that a small zone > >> >> >would see a similar pointless iterations... > >> >> > > >> >> > >> >> Hmm... No special reason, just not thought about this implementation. And > >> >> actually I just do the similar thing as in zone_spanned_pages_in_node(), in > >> >> which also return 0 when there is no overlap. > >> >> > >> >> BTW, I don't get your point. You wish to put the check in > >> >> for_each_mem_pfn_range() definition? > >> > > >> >My point was that you are handling one special case (an empty zone) but > >> >the underlying problem is that __absent_pages_in_range might be wasting > >> >cycles iterating over memblocks that are way outside of the given pfn > >> >range. At least this is my understanding. If you fix that you do not > >> >need the special case, right? > >> >-- > >> >Michal Hocko > >> >SUSE Labs > >> > >> > Not really, sorry, this area is full of awkward and subtle code when new > >> > changes build on top of previous awkwardness/surprises. Any cleanup > >> > would be really appreciated. That is the reason I didn't like the > >> > initial check all that much. > >> > >> Looks my fetchmail failed to get your last reply. So I copied it here. > >> > >> Yes, the change here looks not that nice, while currently this is what I can't > >> come up with. > > > >THen I will suggest dropping this patch from the mmotm tree because it > >doesn't sound like a big improvement and I would encourage you or > >anybody else to take a deeper look and unclutter this area to be more > >readable and better maintainable. > > Hi, Michal > > I don't get your point, which part of the code makes you feel uncomfortable? It adds a check which would better be handled at a different level. I've tried to explain what are my concerns about quick&dirty solutions in this area. I would agree to add the check as a immediate workaround if this had some measurable benefits but the changelog doesn't mention any. So I do not really see this as an improvement in the end. If we want to address the suboptimal code, let's do it properly rather than spewing ifs all over the code. -- Michal Hocko SUSE Labs -- 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>
