On 10/06/25 at 06:45pm, David Hildenbrand 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.
Agree. And I saw Jiri has excluded the crashk_cma_ranges[] from the dumped content via elf_header_exclude_ranges(). Have you encountered a real problem about the dumping, or you are just worried about it? > > > > > 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. Talking about the pages in CMA except of crashk_cma_ranges[], zsmalloc/zswap is true as anon mem and can be discarded. I am wondering if there's any driver or kernel pages residing in CMA and being worth to dump out.
