Messages in this thread | | | Subject | Re: [PATCH v2 0/4] arm64: drop pfn_valid_within() and simplify pfn_valid() | From | Kefeng Wang <> | Date | Thu, 22 Apr 2021 23:28:24 +0800 |
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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@linux.ibm.com> >>> >>> 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? 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 ?
> >> "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@arm.com/ >>
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