On 13 Jul 2021, at 6:24, David Hildenbrand wrote: > On 13.07.21 12:22, Mike Rapoport wrote: >> On Tue, Jul 13, 2021 at 11:51:46AM +0200, David Hildenbrand wrote: >>> On 13.07.21 10:00, Mike Rapoport wrote: >>>> From: Mike Rapoport <rppt@xxxxxxxxxxxxx> >>>> >>>> After recent changes in freeing of the unused parts of the memory map and >>>> rework of pfn_valid() in arm and arm64 there are no architectures that can >>>> have holes in the memory map within a pageblock and so nothing can enable >>>> CONFIG_HOLES_IN_ZONE which guards non trivial implementation of >>>> pfn_valid_within(). >>>> >>>> With that, pfn_valid_within() is always hardwired to 1 and can be >>>> completely removed. >>>> >>>> Remove calls to pfn_valid_within() and CONFIG_HOLES_IN_ZONE. >>>> >>>> Signed-off-by: Mike Rapoport <rppt@xxxxxxxxxxxxx> >>> >>> There is currently the discussion to increase MAX_ORDER, for example, to >>> cover 1GiB instead of 4MiB on x86-64. This would mean that we could >>> suddenly, again, have holes insides MAX_ORDER - 1 pages. >>> >>> So I assume if we ever go down that path, we'll need something like this >>> again. >> >> It depends whether pageblock_order will be also increased. PFN walkers rely >> on continuity of pageblocks rather than MAX_ORDER chunks, so if >> pageblock_order won't change, there won't be need to check for pfn_valid() >> inside a pageblock. > > I'm pushing for letting pageblocks stay untouched, so good to know! > > (we still have this crazy special case of pageblocks > MAX_ORDER - 1 right now, which I think we should just eliminate) I am working on this right now. After I increase MAX_ORDER above SECTION_SIZE_BITS, holes can appear in a zone even on x86_64 and pfn_valid_within(), which is currently set to 1, is needed to be pfn_valid(). That seems to be sufficient to make increasing MAX_ORDER work. For my use case, I might revive pfn_valid_within() if MAX_ORDER is configured to be above SECTION_SIZE_BITS. Let me know if there is any better alternative. Thanks. — Best Regards, Yan, Zi
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