Hi David, On Tue, Oct 7, 2025 at 5:45 AM David Hildenbrand <[email protected]> wrote: > > On 06.10.25 18:25, Breno Leitao wrote: > > On Mon, Oct 06, 2025 at 10:16:26AM +0200, David Hildenbrand wrote: > >> On 03.10.25 17:51, Breno Leitao wrote: > >>> Hello Jiri, > >>> > >>> On Thu, Jun 12, 2025 at 12:11:19PM +0200, Jiri Bohac wrote: > >>> > >>>> Currently this is only the case for memory ballooning and zswap. Such > >>>> movable > >>>> memory will be missing from the vmcore. User data is typically not > >>>> dumped by > >>>> makedumpfile. > >>> > >>> For zswap and zsmalloc pages, I'm wondering whether these pages will be > >>> missing > >>> from the vmcore, or if there's a possibility they might be present but > >>> corrupted—especially since they could reside in the CMA region, which may > >>> be > >>> overwritten by the kdump environment. > >> > >> That's not different to ordinary user pages residing on these areas, right? > > > > Will zsmalloc on CMA pages be marked as "userpages"? > > No, but they should have the zsmalloc page type set. > > > > > makedump file iterates over the pfns and check for a few flags before > > "copying" them to disk. > > > > In makedumpfile, userpages are basically discarded if they are anonymous > > pages: > > #define isAnon(mapping, flags, _mapcount) \ > > (((unsigned long)mapping & PAGE_MAPPING_ANON) != 0 && > > !isSlab(flags, > > _mapcount)) > > > > > > https://github.com/makedumpfile/makedumpfile/blob/master/makedumpfile.h#L164 > > > > called from: > > > > https://github.com/makedumpfile/makedumpfile/blob/master/makedumpfile.c#L6671 > > > > For zsmalloc pages in the CMA, The page struct (pfn)) is marked with old > > page struct (from the first kernel), but, the content has changed > > (replaced by kdump environment - 2nd kernel). > > > > So, whatever decision makedumpfile does based on the PFN, it will dump > > incorrect data, given that the page content does not match the data > > anymore. > > Right. > > > > > If my understanding is valid, we don't want to dump any page that points > > to the PFN, because they will probably have garbage. > > My theory is that barely anybody will go ahead and check compressed page > content, but I agree. We should filter them out. > > > > > That said, I see two options: > > > > 1) Ignore the CMA area completely in makedump. > > - I don't think there is any way to find that area today. The kernel > > might need to print the CMA region somewhere (/proc/iomem?) > > /proc/iomem in the newkernel should indicate the memory region as System > RAM (for the new kernel). That can just be filtered out in any case: > dumping memory of the new kernel does not make sense in any case. > > > > > 2) Given that most of the memory in CMA will be anonymous memory, and > > already discard by other rules, just add an additional entry for > > zsmalloc pages. > > > > Talking to Kirill offline, it seems we can piggy back on MovableOps > > page flag. > > We should likely check the page type instead if we go down that path.
If choosing a proper page type/flag is hard, maybe an ongoing new feature for makedumpfile can help with that. In short, if we can get a workable page flag for CMA to get filtered, then proceed as usual, If cannot, then we can use eppic/btf/kallsyms[1] in makedumpfile to programmably determine page type and filter it out. See the program for determining amdgpu's mm pages[2]. [1]: https://lore.kernel.org/kexec/[email protected]/T/#m901bf1413b844648c86e8a84d75b66d0531b9f92 [2]: https://lore.kernel.org/kexec/[email protected]/T/#m38362d258e3b0bdc14a64e54a6acd5b85810ca26 Cheers, Tao Liu > > -- > Cheers > > David / dhildenb >
