On Tue 24-07-18 11:47:02, Vlastimil Babka wrote: > On 07/23/2018 02:30 PM, Michal Hocko wrote: > > On Mon 23-07-18 13:45:18, Vlastimil Babka wrote: > >> On 07/20/2018 02:34 PM, David Hildenbrand wrote: > >>> Dumping tools (like makedumpfile) right now don't exclude reserved pages. > >>> So reserved pages might be access by dump tools although nobody except > >>> the owner should touch them. > >> > >> Are you sure about that? Or maybe I understand wrong. Maybe it changed > >> recently, but IIRC pages that are backing memmap (struct pages) are also > >> PG_reserved. And you definitely do want those in the dump. > > > > You are right. reserve_bootmem_region will make all early bootmem > > allocations (including those backing memmaps) PageReserved. I have asked > > several times but I haven't seen a satisfactory answer yet. Why do we > > even care for kdump about those. If they are reserved the nobody should > > really look at those specific struct pages and manipulate them. Kdump > > tools are using a kernel interface to read the content. If the specific > > content is backed by a non-existing memory then they should simply not > > return anything. > > When creating a crashdump, I definitely need the pages containing memmap > included in the dump, so I can inspect the struct pages. But this is a > bit recursive issue, so I'll try making it clearer: > > 1) there are kernel pages with data (e.g. slab) that I typically need in > the dump, and are not PageReserved > 2) there are struct pages for pages 1) in the memmap that physically > hold the pageflags for 1), and these are PageReserved > 3) there are struct pages for pages 2) somewhere else in the memmap, > physically hold the pageflags for 2). They are probably also > PageReserved themselves ? and self-referencing. > > Excluding PageReserved from dump means there won't be cases 2) and 3) in > the dump, which at least for case 2) is making such dump almost useless > in many cases. Yes, we cannot simply exclude all PageReserved pages. I was merely suggesting to rule out new special PageReserved pages that are denoting offline pages. The same could be applied to HWPoison pages -- Michal Hocko SUSE Labs
