On Thu, Apr 22, 2021 at 11:28:24PM +0800, Kefeng Wang wrote: > > On 2021/4/22 15:29, Mike Rapoport wrote: > > On Thu, Apr 22, 2021 at 03:00:20PM +0800, Kefeng Wang wrote: > > > On 2021/4/21 14:51, Mike Rapoport wrote: > > > > From: Mike Rapoport <rppt@xxxxxxxxxxxxx> > > > > > > > > Hi, > > > > > > > > These patches aim to remove CONFIG_HOLES_IN_ZONE and essentially hardwire > > > > pfn_valid_within() to 1. > > > > > > > > The idea is to mark NOMAP pages as reserved in the memory map and restore > > > > the intended semantics of pfn_valid() to designate availability of struct > > > > page for a pfn. > > > > > > > > With this the core mm will be able to cope with the fact that it cannot use > > > > NOMAP pages and the holes created by NOMAP ranges within MAX_ORDER blocks > > > > will be treated correctly even without the need for pfn_valid_within. > > > > > > > > The patches are only boot tested on qemu-system-aarch64 so I'd really > > > > appreciate memory stress tests on real hardware. > > > > > > > > If this actually works we'll be one step closer to drop custom pfn_valid() > > > > on arm64 altogether. > > > Hi Mike，I have a question, without HOLES_IN_ZONE, the pfn_valid_within() in > > > move_freepages_block()->move_freepages() > > > will be optimized, if there are holes in zone, the 'struce page'(memory map) > > > for pfn range of hole will be free by > > > free_memmap(), and then the page traverse in the zone(with holes) from > > > move_freepages() will meet the wrong page， > > > then it could panic at PageLRU(page) test, check link[1], > > First, HOLES_IN_ZONE name us hugely misleading, this configuration option > > has nothing to to with memory holes, but rather it is there to deal with > > holes or undefined struct pages in the memory map, when these holes can be > > inside a MAX_ORDER_NR_PAGES region. > > > > In general pfn walkers use pfn_valid() and pfn_valid_within() to avoid > > accessing *missing* struct pages, like those that are freed at > > free_memmap(). But on arm64 these tests also filter out the nomap entries > > because their struct pages are not initialized. > > > > The panic you refer to happened because there was an uninitialized struct > > page in the middle of MAX_ORDER_NR_PAGES region because it corresponded to > > nomap memory. > > > > With these changes I make sure that such pages will be properly initialized > > as PageReserved and the pfn walkers will be able to rely on the memory map. > > > > Note also, that free_memmap() aligns the parts being freed on MAX_ORDER > > boundaries, so there will be no missing parts in the memory map within a > > MAX_ORDER_NR_PAGES region. > > Ok, thanks, we met a same panic like the link on arm32(without > HOLES_IN_ZONE), > > the scheme for arm64 could be suit for arm32, right? In general yes. You just need to make sure that usage of pfn_valid() in arch/arm does not presume that it tests something beyond availability of struct page for a pfn. > I will try the patchset with some changes on arm32 and give some > feedback. > > Again, the stupid question, where will mark the region of memblock with > MEMBLOCK_NOMAP flag ? Not sure I understand the question. The memory regions with "nomap" property in the device tree will be marked MEMBLOCK_NOMAP. > > > "The idea is to mark NOMAP pages as reserved in the memory map", I see the > > > patch2 check memblock_is_nomap() in memory region > > > of memblock, but it seems that memblock_mark_nomap() is not called(maybe I > > > missed), then memmap_init_reserved_pages() won't > > > work, so should the HOLES_IN_ZONE still be needed for generic mm code? > > > > > > [1] https://lore.kernel.org/linux-arm-kernel/541193a6-2bce-f042-5bb2-88913d5f1047@xxxxxxx/ > > > -- Sincerely yours, Mike.
