On Wed, Jun 24, 2020 at 10:51:08AM +0200, David Hildenbrand wrote: >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, I have added this above the "if" check. > >-- >Thanks, > >David / dhildenb -- Wei Yang Help you, Help me
