On Tue, Oct 27, 2020 at 09:46:35AM +0100, David Hildenbrand wrote: > On 27.10.20 09:38, Mike Rapoport wrote: > > On Mon, Oct 26, 2020 at 06:05:30PM +0000, Edgecombe, Rick P wrote: > > > > > Beyond whatever you are seeing, for the latter case of new things > > > getting introduced to an interface with hidden dependencies... Another > > > edge case could be a new caller to set_memory_np() could result in > > > large NP pages. None of the callers today should cause this AFAICT, but > > > it's not great to rely on the callers to know these details. > > A caller of set_memory_*() or set_direct_map_*() should expect a failure > > and be ready for that. So adding a WARN to safe_copy_page() is the first > > step in that direction :) > > > > I am probably missing something important, but why are we saving/restoring > the content of pages that were explicitly removed from the identity mapping > such that nobody will access them? Actually, we should not be saving/restoring free pages during hibernation as there are several calls to mark_free_pages() that should exclude the free pages from the snapshot. I've tried to find why the fix that maps/unmaps a page to save it was required at the first place, but I could not find bug reports. The closest I've got is an email from Rafael that asked to update "hibernate: handle DEBUG_PAGEALLOC" patch: https://lore.kernel.org/linux-pm/200802200133.44098.rjw@xxxxxxx/ Could it be that safe_copy_page() tries to workaround a non-existent problem? -- Sincerely yours, Mike.
