On 24.06.20 05:56, Wei Yang wrote: > On Wed, Jun 24, 2020 at 11:52:36AM +0800, Baoquan He wrote: >> On 06/24/20 at 11:46am, Wei Yang wrote: >>> On Wed, Jun 24, 2020 at 09:47:37AM +0800, Baoquan He wrote: >>>> On 06/23/20 at 05:21pm, Dan Williams wrote: >>>>> On Tue, Jun 23, 2020 at 2:43 AM Wei Yang >>>>> <richard.weiyang@xxxxxxxxxxxxxxxxx> wrote: >>>>>> >>>>>> For early sections, we assumes its memmap will never be partially >>>>>> removed. But current behavior breaks this. >>>>> >>>>> Where do we assume that? >>>>> >>>>> The primary use case for this was mapping pmem that collides with >>>>> System-RAM in the same 128MB section. That collision will certainly be >>>>> depopulated on-demand depending on the state of the pmem device. So, >>>>> I'm not understanding the problem or the benefit of this change. >>>> >>>> I was also confused when review this patch, the patch log is a little >>>> short and simple. From the current code, with SPARSE_VMEMMAP enabled, we >>>> do build memmap for the whole memory section during boot, even though >>>> some of them may be partially populated. We just mark the subsection map >>>> for present pages. >>>> >>>> Later, if pmem device is mapped into the partially boot memory section, >>>> we just fill the relevant subsection map, do return directly, w/o building >>>> the memmap for it, in section_activate(). Because the memmap for the >>>> unpresent RAM part have been there. I guess this is what Wei is trying to >>>> do to keep the behaviour be consistent for pmem device adding, or >>>> pmem device removing and later adding again. >>>> >>>> Please correct me if I am wrong. >>> >>> You are right here. >>> >>>> >>>> To me, fixing it looks good. But a clear doc or code comment is >>>> necessary so that people can understand the code with less time. >>>> Leaving it as is doesn't cause harm. I personally tend to choose >>>> the former. >>>> >>> >>> The former is to add a clear doc? >> >> Sorry for the confusion. The former means the fix in your patch. Maybe a >> improved log and some code comment adding can make it more perfect. >> > > Sure, I would try to add more log and comments, in case you have some good > suggestion, just let me know :) > We have documented this is section_activate() and pfn_valid() sufficiently. Maybe add a pointer like /* * The memmap of early sections is always fully populated. See * section_activate() and pfn_valid() . */ -- Thanks, David / dhildenb
