Hello, On Fri, 2013-08-23 at 09:04 -0400, Tejun Heo wrote: > On Thu, Aug 22, 2013 at 04:17:41PM -0600, Toshi Kani wrote: > > I am relatively new to Linux, so I am not a good person to elaborate > > this. From my experience on other OS, huge pages helped for the kernel, > > but did not necessarily help user applications. It depended on > > applications, which were not niche cases. But Linux may be different, > > so I asked since you seemed confident. I'd appreciate if you can point > > us some data that endorses your statement. > > We are talking about the kernel linear mapping which is created during > early boot, so if it's available and useable there's no reason not to > use it. Exceptions would be earlier processors which didn't do 1G > mappings or e820 maps with a lot of holes. For CPUs used in NUMA > configurations, the former has been history for a bit now. Can't be > sure about the latter but it'd be surprising for that to affect large > amount of memory in the systems that are of interest here. Ooh, that > reminds me that we probably wanna go back to 1G + MTRR mapping under > 4G. We're currently creating a lot of mapping holes. Thanks for the explanation. > > My worry is that the code is unlikely tested with the special logic when > > someone makes code changes to the page tables. Such code can easily be > > broken in future. > > Well, I wouldn't consider flipping the direction of allocation to be > particularly difficult to get right especially when compared to > bringing in ACPI tables into the mix. > > > To answer your other question/email, I believe Tang's next step is to > > support local page tables. This is why we think pursing SRAT earlier is > > the right direction. > > Given 1G mappings, is that even a worthwhile effort? I'm getting even > more more skeptical. With 1G mappings, I agree that it won't make much difference. I still think acpi table info should be available earlier, but I do not think I can convince you on this. This can be religious debate. Tang, what do you think? Are you OK to try Tejun's suggestion as well? Thanks, -Toshi -- 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>