On Wed, May 21, 2025 at 03:44:32PM +0200, David Hildenbrand wrote: > No, the code is confusing. > > All pages are PageOffline. Only the ones that have not been onlined are *in > addition* PageDirty. > > The relevant bit is documented in page-flags.h: > > "When a memory block gets onlined, all pages are initialized with a refcount > of 1 and PageOffline(). generic_online_page() will take care of clearing > PageOffline()."
Ah ok, I see it in __free_pages_core(). > > - If we want to release logically-offline pages belonging to an onlined > > memory-block, > > we ClearDirty them and be done > > PageOffline gets cleared in both cases: See the comment in > virtio_mem_clear_fake_offline() > > "/* generic_online_page() will clear PageOffline(). */" > > I'll note that I am planning on removing that PageDirty() handling > completely, and also letting handling PageOffline() clearing be always > performed by memory freeing core (the latter is easier to achieve). Cool, I think that would be much clearer. > When re-onlining, the core will set them all PageOffline, and virtio-mem > will intercept page onlining using the page_online_cb. > > virtio-mem will then online the actually plugged parts (-> > generic_online_page(), which clears PageOffline and exposes them to the > buddy) and set the unplugged/hole parts as PageOfflineSkipabble again. > > That logic resides in virtio_mem_online_page_cb(). Sorry, I had to re-cache this. Ok, I think that now I caught up with the code. I see that we mark it Offline in memmap_init_range(), and then __free_pages_core() will clear the flag before releasing them to the buddy. Ok, I think it is much clear now, thanks for helping me out with the details! -- Oscar Salvador SUSE Labs
