On Thu, 2013-10-10 at 18:19 -0400, Tejun Heo wrote: > On Thu, Oct 10, 2013 at 01:17:10PM -0600, Toshi Kani wrote: > > In earlier discussions, Tejun pointed out that huge mappings dismiss the > > benefit of local page tables. > > > > https://lkml.org/lkml/2013/8/23/245 > > This is going nowhere. If we're assuming use of large mappings, none > of this matters. The pagetable is gonna be small no matter what and > locating it near kernel image doesn't really impact anything whether > hotplug is gonna be per-node or per-device. Short of the ability to > relocate kernel image itself, parsing or not parsing SRAT early > doesn't lead to anything of consequence. What are we even arguing > about? That's what bothers me about this effort. Nobody seems to > have actually thought it through. Calm down, please. I simply referred the thread where we had discussed on this matter and agreed up on, so that we do not have to repeat the same discussion again. > To summarize, > > * To do local page table, full ACPI device hierarchy should be parsed. > > * Local page table is pointless if you assume huge mappings and the > plan is to assume huge mappings so that only SRAT is necessary > before allocating page tables. > > * But if you assume huge mappings, it doesn't make material difference > whether the page table is after the kernel image or near the top of > non-hotpluggable memory. It's tiny anyway. > > * So, what's the point of pulling SRAT parsing into early boot? If we > assume huge mappings, it doesn't make any material difference for > either per-node or per-device unplug - it's tiny. If we don't > assume huge mappings, we're talking about parsing full ACPI device > tree before building pagetable. Let's say that's something we can > accept. Is the benefit worthwhile? Doing all that just for debug > configs? Is that something people are actually arguing for? Sure, > if it works without too much effort, it's great, but do we really > wanna do all that and update page table allocation so that > everything is per-device just to support debug configs, for real? > > I'm not asking for super concrete plan but right now people working on > this don't seem to have much idea of what the goals are or why they > want certain things and the discussions naturally repeat themselves. > FWIW, I'm getting to a point where I think nacking the whole series is > the right thing to do here. The patchset out for reviewing does not pull SRAT parsing into early boot. 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>