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Message-ID: <f8ee2f3f-d0ed-3291-ec04-f7f754ab1931@linux.alibaba.com>
Date: Fri, 1 Jul 2022 12:36:00 +0800
From: "guanghui.fgh" <guanghuifeng@...ux.alibaba.com>
To: Mike Rapoport <rppt@...nel.org>
Cc: baolin.wang@...ux.alibaba.com, catalin.marinas@....com,
will@...nel.org, akpm@...ux-foundation.org, david@...hat.com,
jianyong.wu@....com, james.morse@....com, quic_qiancai@...cinc.com,
christophe.leroy@...roup.eu, jonathan@...ek.ca,
mark.rutland@....com, thunder.leizhen@...wei.com,
anshuman.khandual@....com, linux-arm-kernel@...ts.infradead.org,
linux-kernel@...r.kernel.org, geert+renesas@...der.be,
ardb@...nel.org, linux-mm@...ck.org, yaohongbo@...ux.alibaba.com,
alikernel-developer@...ux.alibaba.com
Subject: Re: [PATCH v3] arm64: mm: fix linear mapping mem access performance
degradation
Thanks.
在 2022/6/30 21:46, Mike Rapoport 写道:
> Hi,
>
> On Thu, Jun 30, 2022 at 06:50:22PM +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 ("arm64: Do not defer reserve_crashkernel() for
>> platforms with no DMA memory zones")
>> commit 0a30c53573b0 ("arm64: mm: Move reserve_crashkernel() into
>> mem_init()")
>> commit 2687275a5843 ("arm64: Force NO_BLOCK_MAPPINGS if crashkernel
>> reservation is required")
>>
>> 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. So the linear mem mapping use block/section mapping
>> as more as possible. We will reduce the cpu dTLB miss conspicuously, and
>> accelerate mem access about 10-20% performance improvement.
>
> ...
>
>> Signed-off-by: Guanghui Feng <guanghuifeng@...ux.alibaba.com>
>> ---
>> arch/arm64/include/asm/mmu.h | 1 +
>> arch/arm64/mm/init.c | 8 +-
>> arch/arm64/mm/mmu.c | 231 ++++++++++++++++++++++++++++++-------------
>> 3 files changed, 168 insertions(+), 72 deletions(-)
>
> ...
>
>> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
>> index 626ec32..4b779cf 100644
>> --- a/arch/arm64/mm/mmu.c
>> +++ b/arch/arm64/mm/mmu.c
>> @@ -42,6 +42,7 @@
>> #define NO_BLOCK_MAPPINGS BIT(0)
>> #define NO_CONT_MAPPINGS BIT(1)
>> #define NO_EXEC_MAPPINGS BIT(2) /* assumes FEAT_HPDS is not used */
>> +#define NO_SEC_REMAPPINGS BIT(3) /* rebuild with non block/sec mapping*/
>>
>> u64 idmap_t0sz = TCR_T0SZ(VA_BITS_MIN);
>> u64 idmap_ptrs_per_pgd = PTRS_PER_PGD;
>> @@ -156,11 +157,12 @@ static bool pgattr_change_is_safe(u64 old, u64 new)
>> }
>>
>> static void init_pte(pmd_t *pmdp, unsigned long addr, unsigned long end,
>> - phys_addr_t phys, pgprot_t prot)
>> + phys_addr_t phys, pgprot_t prot, int flags)
>> {
>> pte_t *ptep;
>>
>> - ptep = pte_set_fixmap_offset(pmdp, addr);
>> + ptep = (flags & NO_SEC_REMAPPINGS) ? pte_offset_kernel(pmdp, addr) :
>> + pte_set_fixmap_offset(pmdp, addr);
>> do {
>> pte_t old_pte = READ_ONCE(*ptep);
>>
>> @@ -176,7 +178,8 @@ static void init_pte(pmd_t *pmdp, unsigned long addr, unsigned long end,
>> phys += PAGE_SIZE;
>> } while (ptep++, addr += PAGE_SIZE, addr != end);
>>
>> - pte_clear_fixmap();
>> + if (!(flags & NO_SEC_REMAPPINGS))
>> + pte_clear_fixmap();
>> }
>>
>> static void alloc_init_cont_pte(pmd_t *pmdp, unsigned long addr,
>> @@ -208,16 +211,59 @@ static void alloc_init_cont_pte(pmd_t *pmdp, unsigned long addr,
>> next = pte_cont_addr_end(addr, end);
>>
>> /* use a contiguous mapping if the range is suitably aligned */
>> - if ((((addr | next | phys) & ~CONT_PTE_MASK) == 0) &&
>> + if (!(flags & NO_SEC_REMAPPINGS) &&
>> + (((addr | next | phys) & ~CONT_PTE_MASK) == 0) &&
>> (flags & NO_CONT_MAPPINGS) == 0)
>> __prot = __pgprot(pgprot_val(prot) | PTE_CONT);
>>
>> - init_pte(pmdp, addr, next, phys, __prot);
>> + init_pte(pmdp, addr, next, phys, __prot, flags);
>>
>> phys += next - addr;
>> } while (addr = next, addr != end);
>> }
>>
>> +static void init_pmd_remap(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;
>> + pmd_t *pmdp;
>> + phys_addr_t map_offset;
>> + 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 & (~NO_SEC_REMAPPINGS));
>> +
>> + 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 & (~NO_SEC_REMAPPINGS));
>> + }
>> + alloc_init_cont_pte(pmdp, addr, next, phys, prot,
>> + pgtable_alloc, flags);
>> + phys += next - addr;
>> + } while (pmdp++, addr = next, addr != end);
>> +}
>
> There is still to much duplicated code here and in init_pud_remap().
>
> Did you consider something like this:
>
> void __init map_crashkernel(void)
> {
> int flags = NO_EXEC_MAPPINGS | NO_BLOCK_MAPPINGS | NO_CONT_MAPPINGS;
> u64 size;
>
> /*
> * check if crash kernel supported, reserved etc
> */
>
>
> size = crashk_res.end + 1 - crashk_res.start;
>
> __remove_pgd_mapping(swapper_pg_dir, __phys_to_virt(start), size);
> __create_pgd_mapping(swapper_pg_dir, crashk_res.start,
> __phys_to_virt(crashk_res.start), size,
> PAGE_KERNEL, early_pgtable_alloc, flags);
> }
>
I'm trying do this.
But I think it's the Inverse Process of mem mapping and also generates
duplicated code(Boundary judgment, pagetable modify).
When removing the pgd mapping, it may split pud/pmd section which also
needs [[[rebuild and clear]]] some pagetable.
> ...
>
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