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Message-ID: <Yr2pT8SLznI6beqS@kernel.org>
Date: Thu, 30 Jun 2022 16:46:55 +0300
From: Mike Rapoport <rppt@...nel.org>
To: Guanghui Feng <guanghuifeng@...ux.alibaba.com>
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
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);
}
...
--
Sincerely yours,
Mike.
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