[PATCH] arm64: mm: fix linear mapping mem access performace degradation
Guanghui Feng
guanghuifeng at linux.alibaba.com
Sun Jun 26 04:10:15 PDT 2022
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
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.
I have tested it with pft(Page Fault Test) and fio, obtained great
performace improvement.
For fio test:
1.prepare ramdisk
modprobe -r brd
modprobe brd rd_nr=1 rd_size=67108864
dmsetup remove_all
wipefs -a --force /dev/ram0
mkfs -t ext4 -E lazy_itable_init=0,lazy_journal_init=0 -q -F /dev/ram0
mkdir -p /fs/ram0
mount -t ext4 /dev/ram0 /fs/ram0
2.prepare fio paremeter in x.fio file:
[global]
bs=4k
ioengine=psync
iodepth=128
size=32G
direct=1
invalidate=1
group_reporting
thread=1
rw=read
directory=/fs/ram0
numjobs=1
[task_0]
cpus_allowed=16
stonewall=1
3.run testcase:
perf stat -e dTLB-load-misses fio x.fio
4.contrast
------------------------
without patch with patch
fio READ aggrb=1493.2MB/s aggrb=1775.3MB/s
dTLB-load-misses 1,818,320,693 438,729,774
time elapsed(s) 70.500326434 62.877316408
user(s) 15.926332000 15.684721000
sys(s) 54.211939000 47.046165000
5.conclusion
Using this patch will reduce dTLB misses and improve performace greatly.
Signed-off-by: Guanghui Feng <guanghuifeng at 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);
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();
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);
+ 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);
+ 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);
+}
+
+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);
+}
+
+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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