From: Jason Gunthorpe <jgg@nvidia•com>
To: David Hildenbrand <david@redhat•com>
Cc: linux-kernel@vger•kernel.org,
Andrew Morton <akpm@linux-foundation•org>,
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Subject: Re: [PATCH RFC 00/35] mm: remove nth_page()
Date: Fri, 22 Aug 2025 11:30:43 -0300 [thread overview]
Message-ID: <20250822143043.GG1311579@nvidia.com> (raw)
In-Reply-To: <20250821200701.1329277-1-david@redhat.com>
On Thu, Aug 21, 2025 at 10:06:26PM +0200, David Hildenbrand wrote:
> As discussed recently with Linus, nth_page() is just nasty and we would
> like to remove it.
>
> To recap, the reason we currently need nth_page() within a folio is because
> on some kernel configs (SPARSEMEM without SPARSEMEM_VMEMMAP), the
> memmap is allocated per memory section.
>
> While buddy allocations cannot cross memory section boundaries, hugetlb
> and dax folios can.
>
> So crossing a memory section means that "page++" could do the wrong thing.
> Instead, nth_page() on these problematic configs always goes from
> page->pfn, to the go from (++pfn)->page, which is rather nasty.
>
> Likely, many people have no idea when nth_page() is required and when
> it might be dropped.
>
> We refer to such problematic PFN ranges and "non-contiguous pages".
> If we only deal with "contiguous pages", there is not need for nth_page().
>
> Besides that "obvious" folio case, we might end up using nth_page()
> within CMA allocations (again, could span memory sections), and in
> one corner case (kfence) when processing memblock allocations (again,
> could span memory sections).
I browsed the patches and it looks great to me, thanks for doing this
Jason
prev parent reply other threads:[~2025-08-22 14:30 UTC|newest]
Thread overview: 96+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-08-21 20:06 [PATCH RFC 00/35] mm: remove nth_page() David Hildenbrand
2025-08-21 20:06 ` [PATCH RFC 01/35] mm: stop making SPARSEMEM_VMEMMAP user-selectable David Hildenbrand
2025-08-21 20:20 ` Zi Yan
2025-08-22 15:09 ` Mike Rapoport
2025-08-22 17:02 ` SeongJae Park
2025-08-21 20:06 ` [PATCH RFC 02/35] arm64: Kconfig: drop superfluous "select SPARSEMEM_VMEMMAP" David Hildenbrand
2025-08-22 15:10 ` Mike Rapoport
2025-08-21 20:06 ` [PATCH RFC 03/35] s390/Kconfig: " David Hildenbrand
2025-08-22 15:11 ` Mike Rapoport
2025-08-21 20:06 ` [PATCH RFC 04/35] x86/Kconfig: " David Hildenbrand
2025-08-22 15:11 ` Mike Rapoport
2025-08-21 20:06 ` [PATCH RFC 05/35] wireguard: selftests: remove CONFIG_SPARSEMEM_VMEMMAP=y from qemu kernel config David Hildenbrand
2025-08-22 15:13 ` Mike Rapoport
2025-09-08 16:47 ` Jason A. Donenfeld
2025-08-21 20:06 ` [PATCH RFC 06/35] mm/page_alloc: reject unreasonable folio/compound page sizes in alloc_contig_range_noprof() David Hildenbrand
2025-08-21 20:23 ` Zi Yan
2025-08-22 17:07 ` SeongJae Park
2025-10-09 4:21 ` Balbir Singh
2025-10-09 6:12 ` David Hildenbrand
2025-10-09 10:25 ` Balbir Singh
2025-10-09 10:30 ` David Hildenbrand
2025-08-21 20:06 ` [PATCH RFC 07/35] mm/memremap: reject unreasonable folio/compound page sizes in memremap_pages() David Hildenbrand
2025-08-22 17:09 ` SeongJae Park
2025-08-21 20:06 ` [PATCH RFC 08/35] mm/hugetlb: check for unreasonable folio sizes when registering hstate David Hildenbrand
2025-08-21 20:06 ` [PATCH RFC 09/35] mm/mm_init: make memmap_init_compound() look more like prep_compound_page() David Hildenbrand
2025-08-22 15:27 ` Mike Rapoport
2025-08-22 18:09 ` David Hildenbrand
2025-08-21 20:06 ` [PATCH RFC 10/35] mm/hugetlb: cleanup hugetlb_folio_init_tail_vmemmap() David Hildenbrand
2025-08-22 4:09 ` Mika Penttilä
2025-08-22 6:24 ` David Hildenbrand
2025-08-23 8:59 ` Mike Rapoport
2025-08-25 12:48 ` David Hildenbrand
2025-08-25 14:32 ` Mike Rapoport
2025-08-25 14:38 ` David Hildenbrand
2025-08-25 14:59 ` Mike Rapoport
2025-08-25 15:42 ` David Hildenbrand
2025-08-25 16:17 ` Mike Rapoport
2025-08-25 16:23 ` David Hildenbrand
2025-08-25 16:58 ` update kernel-doc for MEMBLOCK_RSRV_NOINIT (was: Re: [PATCH RFC 10/35] mm/hugetlb: cleanup hugetlb_folio_init_tail_vmemmap()) Mike Rapoport
2025-08-25 18:32 ` update kernel-doc for MEMBLOCK_RSRV_NOINIT David Hildenbrand
2025-10-09 1:07 ` update kernel-doc for MEMBLOCK_RSRV_NOINIT (was: Re: [PATCH RFC 10/35] mm/hugetlb: cleanup hugetlb_folio_init_tail_vmemmap()) patchwork-bot+linux-riscv
2025-08-21 20:06 ` [PATCH RFC 11/35] mm: sanity-check maximum folio size in folio_set_order() David Hildenbrand
2025-08-21 20:36 ` Zi Yan
2025-08-21 20:06 ` [PATCH RFC 12/35] mm: limit folio/compound page sizes in problematic kernel configs David Hildenbrand
2025-08-21 20:46 ` Zi Yan
2025-08-21 20:49 ` David Hildenbrand
2025-08-21 20:50 ` Zi Yan
2025-08-24 13:24 ` Mike Rapoport
2025-08-21 20:06 ` [PATCH RFC 13/35] mm: simplify folio_page() and folio_page_idx() David Hildenbrand
2025-08-21 20:55 ` Zi Yan
2025-08-21 21:00 ` David Hildenbrand
2025-08-21 20:06 ` [PATCH RFC 14/35] mm/mm/percpu-km: drop nth_page() usage within single allocation David Hildenbrand
2025-08-21 20:06 ` [PATCH RFC 15/35] fs: hugetlbfs: remove nth_page() usage within folio in adjust_range_hwpoison() David Hildenbrand
2025-08-21 20:06 ` [PATCH RFC 16/35] mm/pagewalk: drop nth_page() usage within folio in folio_walk_start() David Hildenbrand
2025-08-21 20:06 ` [PATCH RFC 17/35] mm/gup: drop nth_page() usage within folio when recording subpages David Hildenbrand
2025-08-21 20:06 ` [PATCH RFC 18/35] io_uring/zcrx: remove "struct io_copy_cache" and one nth_page() usage David Hildenbrand
2025-08-22 11:32 ` Pavel Begunkov
2025-08-22 13:59 ` David Hildenbrand
2025-08-27 9:43 ` Pavel Begunkov
2025-08-21 20:06 ` [PATCH RFC 19/35] io_uring/zcrx: remove nth_page() usage within folio David Hildenbrand
2025-08-21 20:06 ` [PATCH RFC 20/35] mips: mm: convert __flush_dcache_pages() to __flush_dcache_folio_pages() David Hildenbrand
2025-08-21 20:06 ` [PATCH RFC 21/35] mm/cma: refuse handing out non-contiguous page ranges David Hildenbrand
2025-08-26 10:45 ` Alexandru Elisei
2025-08-26 11:04 ` David Hildenbrand
2025-08-26 13:03 ` Alexandru Elisei
2025-08-26 13:08 ` David Hildenbrand
2025-08-26 13:11 ` Alexandru Elisei
2025-08-21 20:06 ` [PATCH RFC 22/35] dma-remap: drop nth_page() in dma_common_contiguous_remap() David Hildenbrand
2025-08-22 8:15 ` Marek Szyprowski
2025-08-21 20:06 ` [PATCH RFC 23/35] scatterlist: disallow non-contigous page ranges in a single SG entry David Hildenbrand
2025-08-22 8:15 ` Marek Szyprowski
2025-08-21 20:06 ` [PATCH RFC 24/35] ata: libata-eh: drop nth_page() usage within " David Hildenbrand
2025-08-22 1:59 ` Damien Le Moal
2025-08-22 6:18 ` David Hildenbrand
2025-08-21 20:06 ` [PATCH RFC 25/35] drm/i915/gem: " David Hildenbrand
2025-08-21 20:06 ` [PATCH RFC 26/35] mspro_block: " David Hildenbrand
2025-08-21 20:06 ` [PATCH RFC 27/35] memstick: " David Hildenbrand
2025-08-21 20:06 ` [PATCH RFC 28/35] mmc: " David Hildenbrand
2025-08-21 20:06 ` [PATCH RFC 29/35] scsi: core: " David Hildenbrand
2025-08-22 18:01 ` Bart Van Assche
2025-08-22 18:10 ` David Hildenbrand
2025-08-21 20:06 ` [PATCH RFC 30/35] vfio/pci: " David Hildenbrand
2025-08-21 20:06 ` [PATCH RFC 31/35] crypto: remove " David Hildenbrand
2025-08-21 20:24 ` Linus Torvalds
2025-08-21 20:29 ` David Hildenbrand
2025-08-21 20:36 ` Linus Torvalds
2025-08-21 20:37 ` David Hildenbrand
2025-08-21 20:40 ` Linus Torvalds
2025-08-21 20:06 ` [PATCH RFC 32/35] mm/gup: drop nth_page() usage in unpin_user_page_range_dirty_lock() David Hildenbrand
2025-08-21 20:06 ` [PATCH RFC 33/35] kfence: drop nth_page() usage David Hildenbrand
2025-08-21 20:32 ` David Hildenbrand
2025-08-21 21:45 ` David Hildenbrand
2025-08-21 20:07 ` [PATCH RFC 34/35] block: update comment of "struct bio_vec" regarding nth_page() David Hildenbrand
2025-08-21 20:07 ` [PATCH RFC 35/35] mm: remove nth_page() David Hildenbrand
2025-08-21 21:37 ` [syzbot ci] " syzbot ci
2025-08-22 14:30 ` Jason Gunthorpe [this message]
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