summaryrefslogtreecommitdiff
path: root/arch/arm
diff options
context:
space:
mode:
authorNicholas Piggin <npiggin@gmail.com>2021-04-29 22:58:10 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2021-04-30 11:20:39 -0700
commit972472c7466b50efed4539694007951a3fc7b95c (patch)
tree228c92551d20e16aaac49583388c1d7359d7fa3c /arch/arm
parentf608788cd2d6cae27d1a3d2253544ca76b353764 (diff)
ARM: mm: add missing pud_page define to 2-level page tables
Patch series "huge vmalloc mappings", v13. The kernel virtual mapping layer grew support for mapping memory with > PAGE_SIZE ptes with commit 0ddab1d2ed66 ("lib/ioremap.c: add huge I/O map capability interfaces"), and implemented support for using those huge page mappings with ioremap. According to the submission, the use-case is mapping very large non-volatile memory devices, which could be GB or TB: https://lore.kernel.org/lkml/1425404664-19675-1-git-send-email-toshi.kani@hp.com/ The benefit is said to be in the overhead of maintaining the mapping, perhaps both in memory overhead and setup / teardown time. Memory overhead for the mapping with a 4kB page and 8 byte page table is 2GB per TB of mapping, down to 4MB / TB with 2MB pages. The same huge page vmap infrastructure can be quite easily adapted and used for mapping vmalloc memory pages without more complexity for arch or core vmap code. However unlike ioremap, vmalloc page table overhead is not a real problem, so the advantage to justify this is performance. Several of the most structures in the kernel (e.g., vfs and network hash tables) are allocated with vmalloc on NUMA machines, in order to distribute access bandwidth over the machine. Mapping these with larger pages can improve TLB usage significantly, for example this reduces TLB misses by nearly 30x on a `git diff` workload on a 2-node POWER9 (59,800 -> 2,100) and reduces CPU cycles by 0.54%, due to vfs hashes being allocated with 2MB pages. [ Other numbers? - The difference is even larger in a guest due to more costly TLB misses. - Eric Dumazet was keen on the network hash performance possibilities. - Other archs? Ding was doing x86 testing. ] The kernel module allocator also uses vmalloc to map module images even on non-NUMA, which can result in high iTLB pressure on highly modular distro type of kernels. This series does not implement huge mappings for modules yet, but it's a step along the way. Rick Edgecombe was looking at that IIRC. The per-cpu allocator similarly might be able to take advantage of this. Also on the todo list. The disadvantages of this I can see are: * Memory fragmentation can waste some physical memory because it will attempt to allocate larger pages to fit the required size, rounding up (once the requested size is >= 2MB). - I don't see it being a big problem in practice unless some user crops up that allocates thousands of 2.5MB ranges. We can tewak heuristics a bit there if needed to reduce peak waste. * Less granular mappings can make the NUMA distribution less balanced. - Similar to the above. - Could also allocate all major system hashes with one allocation up-front and spread them all across the one block, which should help overall NUMA distribution and reduce fragmentation waste. * Callers might expect something about the underlying allocated pages. - Tried to keep the apperance of base PAGE_SIZE pages throughout the APIs and exposed data structures. - Added a VM_NO_HUGE_VMAP flag to hammer troublesome cases with. - Finally, added a nohugevmalloc boot option to turn it off (independent of nohugeiomap). This patch (of 14): ARM uses its own PMD folding scheme which is missing pud_page which should just pass through to pmd_page. Move this from the 3-level page table to common header. Link: https://lkml.kernel.org/r/20210317062402.533919-2-npiggin@gmail.com Signed-off-by: Nicholas Piggin <npiggin@gmail.com> Cc: Russell King <linux@armlinux.org.uk> Cc: Ding Tianhong <dingtianhong@huawei.com> Cc: Uladzislau Rezki (Sony) <urezki@gmail.com> Cc: Borislav Petkov <bp@alien8.de> Cc: Catalin Marinas <catalin.marinas@arm.com> Cc: Christoph Hellwig <hch@lst.de> Cc: "H. Peter Anvin" <hpa@zytor.com> Cc: Ingo Molnar <mingo@redhat.com> Cc: Miaohe Lin <linmiaohe@huawei.com> Cc: Michael Ellerman <mpe@ellerman.id.au> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Will Deacon <will@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'arch/arm')
-rw-r--r--arch/arm/include/asm/pgtable-3level.h2
-rw-r--r--arch/arm/include/asm/pgtable.h3
2 files changed, 3 insertions, 2 deletions
diff --git a/arch/arm/include/asm/pgtable-3level.h b/arch/arm/include/asm/pgtable-3level.h
index 2b85d175e999..d4edab51a77c 100644
--- a/arch/arm/include/asm/pgtable-3level.h
+++ b/arch/arm/include/asm/pgtable-3level.h
@@ -186,8 +186,6 @@ static inline pte_t pte_mkspecial(pte_t pte)
#define pmd_write(pmd) (pmd_isclear((pmd), L_PMD_SECT_RDONLY))
#define pmd_dirty(pmd) (pmd_isset((pmd), L_PMD_SECT_DIRTY))
-#define pud_page(pud) pmd_page(__pmd(pud_val(pud)))
-#define pud_write(pud) pmd_write(__pmd(pud_val(pud)))
#define pmd_hugewillfault(pmd) (!pmd_young(pmd) || !pmd_write(pmd))
#define pmd_thp_or_huge(pmd) (pmd_huge(pmd) || pmd_trans_huge(pmd))
diff --git a/arch/arm/include/asm/pgtable.h b/arch/arm/include/asm/pgtable.h
index c02f24400369..d63a5bb6bd0c 100644
--- a/arch/arm/include/asm/pgtable.h
+++ b/arch/arm/include/asm/pgtable.h
@@ -166,6 +166,9 @@ extern struct page *empty_zero_page;
extern pgd_t swapper_pg_dir[PTRS_PER_PGD];
+#define pud_page(pud) pmd_page(__pmd(pud_val(pud)))
+#define pud_write(pud) pmd_write(__pmd(pud_val(pud)))
+
#define pmd_none(pmd) (!pmd_val(pmd))
static inline pte_t *pmd_page_vaddr(pmd_t pmd)