Messages in this thread | | | Date | Tue, 28 Jun 2022 11:22:48 +0800 | Subject | Re: [PATCH] arm64: mm: fix linear mapping mem access performace degradation | From | "guanghui.fgh" <> |
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Thanks.
在 2022/6/28 9:50, Kefeng Wang 写道: > > On 2022/6/28 0:49, Mike Rapoport wrote: >> On Mon, Jun 27, 2022 at 06:46:50PM +0800, guanghui.fgh wrote: >>> 在 2022/6/27 17:49, Mike Rapoport 写道: >>>> On Mon, Jun 27, 2022 at 05:24:10PM +0800, guanghui.fgh wrote: >>>>> 在 2022/6/27 14:34, Mike Rapoport 写道: >>>>> >>>>> On Sun, Jun 26, 2022 at 07:10:15PM +0800, Guanghui Feng wrote: >>>>> >>>>> The arm64 can build 2M/1G block/sectiion mapping. When >>>>> using DMA/DMA32 zone >>>>> (enable crashkernel, disable rodata full, disable >>>>> kfence), the mem_map will >>>>> use non block/section mapping(for crashkernel requires to >>>>> shrink the region >>>>> in page granularity). But it will degrade performance >>>>> when doing larging >>>>> continuous mem access in kernel(memcpy/memmove, etc). >>>>> >>>>> There are many changes and discussions: >>>>> commit 031495635b46 >>>>> commit 1a8e1cef7603 >>>>> commit 8424ecdde7df >>>>> commit 0a30c53573b0 >>>>> commit 2687275a5843 >>>>> >>>>> Please include oneline summary of the commit. (See section >>>>> "Describe your >>>>> changes" in Documentation/process/submitting-patches.rst) >>>>> >>>>> OK, I will add oneline summary in the git commit messages. >>>>> >>>>> This patch changes mem_map to use block/section mapping >>>>> with crashkernel. >>>>> Firstly, do block/section mapping(normally 2M or 1G) for >>>>> all avail mem at >>>>> mem_map, reserve crashkernel memory. And then walking >>>>> pagetable to split >>>>> block/section mapping to non block/section >>>>> mapping(normally 4K) [[[only]]] >>>>> for crashkernel mem. >>>>> >>>>> This already happens when ZONE_DMA/ZONE_DMA32 are disabled. >>>>> Please explain >>>>> why is it Ok to change the way the memory is mapped with >>>>> ZONE_DMA/ZONE_DMA32 enabled. >>>>> >>>>> In short: >>>>> >>>>> 1.building all avail mem with block/section mapping(normally >>>>> 1G/2M) without >>>>> inspecting crashkernel >>>>> 2. Reserve crashkernel mem as same as previous doing >>>>> 3. only change the crashkernle mem mapping to normal >>>>> mapping(normally 4k). >>>>> With this method, there are block/section mapping as more as possible. >>>> This does not answer the question why changing the way the memory is >>>> mapped >>>> when there is ZONE_DMA/DMA32 and crashkernel won't cause a regression. >>>> >>> 1.Quoted messages from arch/arm64/mm/init.c >>> >>> "Memory reservation for crash kernel either done early or deferred >>> depending on DMA memory zones configs (ZONE_DMA) -- >>> >>> In absence of ZONE_DMA configs arm64_dma_phys_limit initialized >>> here instead of max_zone_phys(). This lets early reservation of >>> crash kernel memory which has a dependency on arm64_dma_phys_limit. >>> Reserving memory early for crash kernel allows linear creation of block >>> mappings (greater than page-granularity) for all the memory bank rangs. >>> In this scheme a comparatively quicker boot is observed. >>> >>> If ZONE_DMA configs are defined, crash kernel memory reservation >>> is delayed until DMA zone memory range size initialization performed in >>> zone_sizes_init(). The defer is necessary to steer clear of DMA zone >>> memory range to avoid overlap allocation. So crash kernel memory >>> boundaries >>> are not known when mapping all bank memory ranges, which otherwise >>> means not >>> possible to exclude crash kernel range from creating block mappings so >>> page-granularity mappings are created for the entire memory range." >>> >>> Namely, the init order: memblock init--->linear mem mapping(4k >>> mapping for >>> crashkernel, requirinig page-granularity changing))--->zone dma >>> limit--->reserve crashkernel. >>> So when enable ZONE DMA and using crashkernel, the mem mapping using 4k >>> mapping. >>> >>> 2.As mentioned above, when linear mem use 4k mapping simply, there is >>> high >>> dtlb miss(degrade performance). >>> This patch use block/section mapping as far as possible with performance >>> improvement. >>> >>> 3.This patch reserve crashkernel as same as the history(ZONE DMA & >>> crashkernel reserving order), and only change the linear mem mapping to >>> block/section mapping. >> Thank you for the explanation. >> >> So if I understand correctly, you suggest to reserve the crash kernel >> memory late regardless of ZONE_DMA/32 configuration and then map that >> memory >> using page level mappings after the memory is reserved. >> >> This makes sense, but I think the patch has a few shortcomings than >> need to >> be addressed. >> >>> Signed-off-by: Guanghui Feng <guanghuifeng@linux.alibaba.com> >>> --- >>> arch/arm64/include/asm/mmu.h | 1 + >>> arch/arm64/mm/init.c | 8 +- >>> arch/arm64/mm/mmu.c | 274 >>> +++++++++++++++++++++++++++++++++++++++---- >>> 3 files changed, 253 insertions(+), 30 deletions(-) >>> >>> diff --git a/arch/arm64/include/asm/mmu.h b/arch/arm64/include/asm/mmu.h >>> index 48f8466..df113cc 100644 >>> --- a/arch/arm64/include/asm/mmu.h >>> +++ b/arch/arm64/include/asm/mmu.h >>> @@ -63,6 +63,7 @@ static inline bool arm64_kernel_unmapped_at_el0(void) >>> extern void arm64_memblock_init(void); >>> extern void paging_init(void); >>> extern void bootmem_init(void); >>> +extern void mapping_crashkernel(void); >> I think map_crashkernel() would be a better name. > > Or a more generic naming (and for other helpers), it's used in > crashkernel for now, > > but maybe more cases. > > >> >>> extern void __iomem *early_io_map(phys_addr_t phys, unsigned long >>> virt); >>> extern void init_mem_pgprot(void); >>> extern void create_pgd_mapping(struct mm_struct *mm, phys_addr_t phys, >>> diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c >>> index 339ee84..0e7540b 100644 >>> --- a/arch/arm64/mm/init.c >>> +++ b/arch/arm64/mm/init.c >>> @@ -388,10 +388,6 @@ void __init arm64_memblock_init(void) >>> } >>> early_init_fdt_scan_reserved_mem(); >>> - >>> - if (!IS_ENABLED(CONFIG_ZONE_DMA) && !IS_ENABLED(CONFIG_ZONE_DMA32)) >>> - reserve_crashkernel(); >>> - >>> high_memory = __va(memblock_end_of_DRAM() - 1) + 1; >>> } >>> @@ -438,8 +434,8 @@ void __init bootmem_init(void) >>> * request_standard_resources() depends on crashkernel's memory >>> being >>> * reserved, so do it here. >>> */ >>> - if (IS_ENABLED(CONFIG_ZONE_DMA) || IS_ENABLED(CONFIG_ZONE_DMA32)) >>> - reserve_crashkernel(); >>> + reserve_crashkernel(); >>> + mapping_crashkernel(); >> This can be called from reserve_crashkernel() directly. >>> memblock_dump_all(); >>> } >>> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c >>> index 626ec32..0672afd 100644 >>> --- a/arch/arm64/mm/mmu.c >>> +++ b/arch/arm64/mm/mmu.c >>> @@ -498,6 +498,256 @@ static int __init enable_crash_mem_map(char *arg) >>> } >>> early_param("crashkernel", enable_crash_mem_map); >>> +#ifdef CONFIG_KEXEC_CORE >>> +static phys_addr_t __init early_crashkernel_pgtable_alloc(int shift) >>> +{ >>> + phys_addr_t phys; >>> + void *ptr; >>> + >>> + phys = memblock_phys_alloc_range(PAGE_SIZE, PAGE_SIZE, 0, >>> + MEMBLOCK_ALLOC_NOLEAKTRACE); >>> + if (!phys) >>> + panic("Failed to allocate page table page\n"); >>> + >>> + ptr = (void *)__phys_to_virt(phys); >>> + memset(ptr, 0, PAGE_SIZE); > add dsb() to ensure page is visible to page table walk? I had consulted from alloc_init_cont_pte. There maybe no need dsb actually. >>> + return phys; >>> +} >>> + >>> +static void init_crashkernel_pte(pmd_t *pmdp, unsigned long addr, >>> + unsigned long end, >>> + phys_addr_t phys, pgprot_t prot) >>> +{ >>> + pte_t *ptep; >>> + ptep = pte_offset_kernel(pmdp, addr); >>> + do { >>> + set_pte(ptep, pfn_pte(__phys_to_pfn(phys), prot)); >>> + phys += PAGE_SIZE; >>> + } while (ptep++, addr += PAGE_SIZE, addr != end); >>> +} >>> + >>> +static void alloc_crashkernel_cont_pte(pmd_t *pmdp, unsigned long addr, >>> + unsigned long end, phys_addr_t phys, >>> + pgprot_t prot, >>> + phys_addr_t (*pgtable_alloc)(int), >>> + int flags) >>> +{ >>> + unsigned long next; >>> + pmd_t pmd = READ_ONCE(*pmdp); >>> + >>> + BUG_ON(pmd_sect(pmd)); >>> + if (pmd_none(pmd)) { >>> + pmdval_t pmdval = PMD_TYPE_TABLE | PMD_TABLE_UXN; >>> + phys_addr_t pte_phys; >>> + >>> + if (flags & NO_EXEC_MAPPINGS) >>> + pmdval |= PMD_TABLE_PXN; >>> + BUG_ON(!pgtable_alloc); >>> + pte_phys = pgtable_alloc(PAGE_SHIFT); >>> + __pmd_populate(pmdp, pte_phys, pmdval); >>> + pmd = READ_ONCE(*pmdp); >>> + } >>> + BUG_ON(pmd_bad(pmd)); >>> + >>> + do { >>> + pgprot_t __prot = prot; >>> + next = pte_cont_addr_end(addr, end); >>> + init_crashkernel_pte(pmdp, addr, next, phys, __prot); >>> + phys += next - addr; >>> + } while (addr = next, addr != end); >>> +} >>> + >>> +static void init_crashkernel_pmd(pud_t *pudp, unsigned long addr, >>> + unsigned long end, phys_addr_t phys, >>> + pgprot_t prot, >>> + phys_addr_t (*pgtable_alloc)(int), int flags) >>> +{ >>> + phys_addr_t map_offset; >>> + unsigned long next; >>> + pmd_t *pmdp; >>> + pmdval_t pmdval; >>> + >>> + pmdp = pmd_offset(pudp, addr); >>> + do { >>> + next = pmd_addr_end(addr, end); >>> + if (!pmd_none(*pmdp) && pmd_sect(*pmdp)) { >>> + phys_addr_t pte_phys = pgtable_alloc(PAGE_SHIFT); >>> + pmd_clear(pmdp); >>> + pmdval = PMD_TYPE_TABLE | PMD_TABLE_UXN; >>> + if (flags & NO_EXEC_MAPPINGS) >>> + pmdval |= PMD_TABLE_PXN; >>> + __pmd_populate(pmdp, pte_phys, pmdval); >>> + flush_tlb_kernel_range(addr, addr + PAGE_SIZE); >>> + >>> + map_offset = addr - (addr & PMD_MASK); >>> + if (map_offset) >>> + alloc_init_cont_pte(pmdp, addr & PMD_MASK, addr, >>> + phys - map_offset, prot, >>> + pgtable_alloc, flags); >>> + >>> + if (next < (addr & PMD_MASK) + PMD_SIZE) >>> + alloc_init_cont_pte(pmdp, next, (addr & PUD_MASK) + >>> + PUD_SIZE, next - addr + phys, >>> + prot, pgtable_alloc, flags); >>> + } >>> + alloc_crashkernel_cont_pte(pmdp, addr, next, phys, prot, >>> + pgtable_alloc, flags); >>> + phys += next - addr; >>> + } while (pmdp++, addr = next, addr != end); >>> +} >>> + >>> +static void alloc_crashkernel_cont_pmd(pud_t *pudp, unsigned long addr, >>> + unsigned long end, phys_addr_t phys, >>> + pgprot_t prot, >>> + phys_addr_t (*pgtable_alloc)(int), >>> + int flags) >>> +{ >>> + unsigned long next; >>> + pud_t pud = READ_ONCE(*pudp); >>> + >>> + /* >>> + * Check for initial section mappings in the pgd/pud. >>> + */ >>> + BUG_ON(pud_sect(pud)); >>> + if (pud_none(pud)) { >>> + pudval_t pudval = PUD_TYPE_TABLE | PUD_TABLE_UXN; >>> + phys_addr_t pmd_phys; >>> + >>> + if (flags & NO_EXEC_MAPPINGS) >>> + pudval |= PUD_TABLE_PXN; >>> + BUG_ON(!pgtable_alloc); >>> + pmd_phys = pgtable_alloc(PMD_SHIFT); >>> + __pud_populate(pudp, pmd_phys, pudval); >>> + pud = READ_ONCE(*pudp); >>> + } >>> + BUG_ON(pud_bad(pud)); >>> + >>> + do { >>> + pgprot_t __prot = prot; >>> + next = pmd_cont_addr_end(addr, end); >>> + init_crashkernel_pmd(pudp, addr, next, phys, __prot, >>> + pgtable_alloc, flags); >>> + phys += next - addr; >>> + } while (addr = next, addr != end); >>> +} >>> + >>> +static void alloc_crashkernel_pud(pgd_t *pgdp, unsigned long addr, >>> + unsigned long end, phys_addr_t phys, >>> + pgprot_t prot, >>> + phys_addr_t (*pgtable_alloc)(int), >>> + int flags) >>> +{ >>> + phys_addr_t map_offset; >>> + unsigned long next; >>> + pud_t *pudp; >>> + p4d_t *p4dp = p4d_offset(pgdp, addr); >>> + p4d_t p4d = READ_ONCE(*p4dp); >>> + pudval_t pudval; >>> + >>> + if (p4d_none(p4d)) { >>> + p4dval_t p4dval = P4D_TYPE_TABLE | P4D_TABLE_UXN; >>> + phys_addr_t pud_phys; >>> + >>> + if (flags & NO_EXEC_MAPPINGS) >>> + p4dval |= P4D_TABLE_PXN; >>> + BUG_ON(!pgtable_alloc); >>> + pud_phys = pgtable_alloc(PUD_SHIFT); >>> + __p4d_populate(p4dp, pud_phys, p4dval); >>> + p4d = READ_ONCE(*p4dp); >>> + } >>> + BUG_ON(p4d_bad(p4d)); >>> + >>> + /* >>> + * No need for locking during early boot. And it doesn't work as >>> + * expected with KASLR enabled. >>> + */ >>> + if (system_state != SYSTEM_BOOTING) >>> + mutex_lock(&fixmap_lock); > It seems that no need to use fixmap_lock. Yes, it's that. >>> + pudp = pud_offset(p4dp, addr); >>> + do { >>> + next = pud_addr_end(addr, end); >>> + if (!pud_none(*pudp) && pud_sect(*pudp)) { >>> + phys_addr_t pmd_phys = pgtable_alloc(PMD_SHIFT); >>> + pud_clear(pudp); >>> + >>> + pudval = PUD_TYPE_TABLE | PUD_TABLE_UXN; >>> + if (flags & NO_EXEC_MAPPINGS) >>> + pudval |= PUD_TABLE_PXN; >>> + __pud_populate(pudp, pmd_phys, pudval); >>> + flush_tlb_kernel_range(addr, addr + PAGE_SIZE); >>> + >>> + map_offset = addr - (addr & PUD_MASK); >>> + if (map_offset) >>> + alloc_init_cont_pmd(pudp, addr & PUD_MASK, addr, >>> + phys - map_offset, prot, >>> + pgtable_alloc, flags); >>> + >>> + if (next < (addr & PUD_MASK) + PUD_SIZE) >>> + alloc_init_cont_pmd(pudp, next, (addr & PUD_MASK) + >>> + PUD_SIZE, next - addr + phys, >>> + prot, pgtable_alloc, flags); >>> + } >>> + alloc_crashkernel_cont_pmd(pudp, addr, next, phys, prot, >>> + pgtable_alloc, flags); >>> + phys += next - addr; >>> + } while (pudp++, addr = next, addr != end); >>> + >>> + if (system_state != SYSTEM_BOOTING) >>> + mutex_unlock(&fixmap_lock); >>> +} >>> + >>> +static void __create_crashkernel_mapping(pgd_t *pgdir, phys_addr_t >>> phys, >>> + unsigned long virt, phys_addr_t size, >>> + pgprot_t prot, >>> + phys_addr_t (*pgtable_alloc)(int), >>> + int flags) >>> +{ >>> + unsigned long addr, end, next; >>> + pgd_t *pgdp = pgd_offset_pgd(pgdir, virt); >>> + >>> + /* >>> + * If the virtual and physical address don't have the same offset >>> + * within a page, we cannot map the region as the caller expects. >>> + */ >>> + if (WARN_ON((phys ^ virt) & ~PAGE_MASK)) >>> + return; >>> + >>> + phys &= PAGE_MASK; >>> + addr = virt & PAGE_MASK; >>> + end = PAGE_ALIGN(virt + size); >>> + >>> + do { >>> + next = pgd_addr_end(addr, end); >>> + alloc_crashkernel_pud(pgdp, addr, next, phys, prot, >>> + pgtable_alloc, flags); >>> + phys += next - addr; >>> + } while (pgdp++, addr = next, addr != end); >>> +} >> __create_crashkernel_mapping() and the helpers it uses resemble very much >> __create_pgd_mapping() and it's helpers. I think a cleaner way would >> be to >> clear section mappings and than call __create_pgd_mapping() for crash >> kernel memory with block/section mappings disabled. > Yes, there are too much duplicated codes, if the handling of crash > reserve memory > is acceptable, we could find a better way(as Mike said) to deal with the > repeat. > Actually, we try something like this before, but I am not sure it is > right way, > and we saw TLB conflict, I will test this patch. OK, I had test this patch and worked well.
>>> +static void __init map_crashkernel(pgd_t *pgdp, phys_addr_t start, >>> + phys_addr_t end, pgprot_t prot, int flags) >>> +{ >>> + __create_crashkernel_mapping(pgdp, start, __phys_to_virt(start), >>> + end - start, prot, >>> + early_crashkernel_pgtable_alloc, flags); >>> +} >> No need for this, you can call __create_crashkernel_mapping() directly >> from >> mapping_crashkernel(). >> >>> + >>> +void __init mapping_crashkernel(void) >>> +{ >>> + if (can_set_direct_map() || IS_ENABLED(CONFIG_KFENCE)) >>> + return; >>> + >>> + if (!crash_mem_map || !crashk_res.end) >>> + return; >>> + >>> + map_crashkernel(swapper_pg_dir, crashk_res.start, >>> + crashk_res.end + 1, PAGE_KERNEL, >>> + NO_BLOCK_MAPPINGS | NO_CONT_MAPPINGS); >>> +} >>> +#else >>> +void __init mapping_crashkernel(void) {} >>> +#endif >>> + >>> static void __init map_mem(pgd_t *pgdp) >>> { >>> static const u64 direct_map_end = _PAGE_END(VA_BITS_MIN); >>> @@ -527,17 +777,6 @@ static void __init map_mem(pgd_t *pgdp) >>> */ >>> memblock_mark_nomap(kernel_start, kernel_end - kernel_start); >>> -#ifdef CONFIG_KEXEC_CORE >>> - if (crash_mem_map) { >>> - if (IS_ENABLED(CONFIG_ZONE_DMA) || >>> - IS_ENABLED(CONFIG_ZONE_DMA32)) >>> - flags |= NO_BLOCK_MAPPINGS | NO_CONT_MAPPINGS; >>> - else if (crashk_res.end) >>> - memblock_mark_nomap(crashk_res.start, >>> - resource_size(&crashk_res)); >>> - } >>> -#endif >>> - >>> /* map all the memory banks */ >>> for_each_mem_range(i, &start, &end) { >>> if (start >= end) >>> @@ -570,19 +809,6 @@ static void __init map_mem(pgd_t *pgdp) >>> * in page granularity and put back unused memory to buddy system >>> * through /sys/kernel/kexec_crash_size interface. >>> */ >>> -#ifdef CONFIG_KEXEC_CORE >>> - if (crash_mem_map && >>> - !IS_ENABLED(CONFIG_ZONE_DMA) && >>> !IS_ENABLED(CONFIG_ZONE_DMA32)) { >>> - if (crashk_res.end) { >>> - __map_memblock(pgdp, crashk_res.start, >>> - crashk_res.end + 1, >>> - PAGE_KERNEL, >>> - NO_BLOCK_MAPPINGS | NO_CONT_MAPPINGS); >>> - memblock_clear_nomap(crashk_res.start, >>> - resource_size(&crashk_res)); >>> - } >>> - } >>> -#endif >>> } >>> void mark_rodata_ro(void) >>> -- >>> 1.8.3.1 >>
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