On 08.04.19 22:10, Alexander Duyck wrote: > On Mon, Apr 8, 2019 at 11:40 AM David Hildenbrand <david@xxxxxxxxxx> wrote: >> >>>>> >>>>> In addition we will need some way to identify which pages have been >>>>> hinted on and which have not. The way I believe easiest to do this >>>>> would be to overload the PageType value so that we could essentially >>>>> have two values for "Buddy" pages. We would have our standard "Buddy" >>>>> pages, and "Buddy" pages that also have the "Offline" value set in the >>>>> PageType field. Tracking the Online vs Offline pages this way would >>>>> actually allow us to do this with almost no overhead as the mapcount >>>>> value is already being reset to clear the "Buddy" flag so adding a >>>>> "Offline" flag to this clearing should come at no additional cost. >>>> >>>> Just nothing here that this will require modifications to kdump >>>> (makedumpfile to be precise and the vmcore information exposed from the >>>> kernel), as kdump only checks for the the actual mapcount value to >>>> detect buddy and offline pages (to exclude them from dumps), they are >>>> not treated as flags. >>>> >>>> For now, any mapcount values are really only separate values, meaning >>>> not the separate bits are of interest, like flags would be. Reusing >>>> other flags would make our life a lot easier. E.g. PG_young or so. But >>>> clearing of these is then the problematic part. >>>> >>>> Of course we could use in the kernel two values, Buddy and BuddyOffline. >>>> But then we have to check for two different values whenever we want to >>>> identify a buddy page in the kernel. >>> >>> Actually this may not be working the way you think it is working. >> >> Trust me, I know how it works. That's why I was giving you the notice. >> >> Read the first paragraph again and ignore the others. I am only >> concerned about makedumpfile that has to be changed. >> >> PAGE_OFFLINE_MAPCOUNT_VALUE >> PAGE_BUDDY_MAPCOUNT_VALUE >> >> Once you find out how these values are used, you should understand what >> has to be changed and where. > > Ugh. Is there an official repo I am supposed to refer to for makedumpfile? > > As far as the changes needed I don't think this would necessitate > additional exports. We could probably just get away with having > makedumpfile generate a new value by simply doing an "&" of the two > values to determine what an offline buddy would be. If need be I can > submit a patch for that. I find it kind of annoying that the kernel is > handling identifying these bits one way, and makedumpfile is doing it > another way. It should have been setup to handle this all the same > way. Here you go: https://sourceforge.net/p/makedumpfile/code/ci/master/tree/ for now we only had one type at a time, so it wasn't an issue. E.g. Buddy or Offline were never used in combination with other types. They had distinct mapcount values. -- Thanks, David / dhildenb
