On Fri, Jan 04, 2013 at 05:04:50AM +0000, Christoffer Dall wrote:

On Thu, Oct 18, 2012 at 12:15 PM, Steve Capper [off-list ref] wrote:

quoted

diff --git a/arch/arm/include/asm/pgtable-3level.h b/arch/arm/include/asm/pgtable-3level.h
index d086f61..31c071f 100644
--- a/arch/arm/include/asm/pgtable-3level.h
+++ b/arch/arm/include/asm/pgtable-3level.h

@@ -85,6 +85,9 @@
 #define L_PTE_DIRTY            (_AT(pteval_t, 1) << 55)        /* unused */
 #define L_PTE_SPECIAL          (_AT(pteval_t, 1) << 56)        /* unused */

+#define PMD_SECT_DIRTY         (_AT(pmdval_t, 1) << 55)
+#define PMD_SECT_SPLITTING     (_AT(pmdval_t, 1) << 57)
+
 /*
  * To be used in assembly code with the upper page attributes.
  */

@@ -166,6 +169,60 @@ static inline pmd_t *pmd_offset(pud_t *pud, unsigned long addr)
 #define pte_mkhuge(pte)                (__pte((pte_val(pte) & ~PMD_TYPE_MASK) | PMD_TYPE_SECT))


+#define pmd_present(pmd)       ((pmd_val(pmd) & PMD_TYPE_MASK) != PMD_TYPE_FAULT)
+#define pmd_young(pmd)         (pmd_val(pmd) & PMD_SECT_AF)
+
+#define __HAVE_ARCH_PMD_WRITE
+#define pmd_write(pmd)         (!(pmd_val(pmd) & PMD_SECT_RDONLY))
+
+#ifdef CONFIG_TRANSPARENT_HUGEPAGE
+#define pmd_trans_huge(pmd)    ((pmd_val(pmd) & PMD_TYPE_MASK) == PMD_TYPE_SECT)
+#define pmd_trans_splitting(pmd) (pmd_val(pmd) & PMD_SECT_SPLITTING)
+#endif
+
+#define PMD_BIT_FUNC(fn,op) \
+static inline pmd_t pmd_##fn(pmd_t pmd) { pmd_val(pmd) op; return pmd; }
+
+PMD_BIT_FUNC(wrprotect,        |= PMD_SECT_RDONLY);
+PMD_BIT_FUNC(mkold,    &= ~PMD_SECT_AF);
+PMD_BIT_FUNC(mksplitting, |= PMD_SECT_SPLITTING);
+PMD_BIT_FUNC(mkwrite,   &= ~PMD_SECT_RDONLY);
+PMD_BIT_FUNC(mkdirty,   |= PMD_SECT_DIRTY);
+PMD_BIT_FUNC(mkyoung,   |= PMD_SECT_AF);
+PMD_BIT_FUNC(mknotpresent, &= ~PMD_TYPE_MASK);

personally I would prefer not to automate the prefixing of pmd_: it
doesn't really save a lot of characters, it doesn't improve
readability and it breaks grep/cscope.

This follows the pte bit functions to a degree.

quoted

+
+#define pmd_mkhuge(pmd)                (__pmd((pmd_val(pmd) & ~PMD_TYPE_MASK) | PMD_TYPE_SECT))
+
+#define pmd_pfn(pmd)           ((pmd_val(pmd) & PHYS_MASK) >> PAGE_SHIFT)

the arm arm says UNK/SBZP, so we should be fine here right? (noone is
crazy enough to try and squeeze some extra information in the extra
bits here or something like that). For clarity, one could consider:

(((pmd_val(pmd) & PMD_MASK) & PHYS_MASK) >> PAGE_SHIFT)

Thanks, yes, it's better to PMD_MASK the value too.

quoted

+#define pfn_pmd(pfn,prot)      (__pmd(((phys_addr_t)(pfn) << PAGE_SHIFT) | pgprot_val(prot)))
+#define mk_pmd(page,prot)      pfn_pmd(page_to_pfn(page),prot)
+
+static inline pmd_t pmd_modify(pmd_t pmd, pgprot_t newprot)
+{
+       const pmdval_t mask = PMD_SECT_USER | PMD_SECT_XN | PMD_SECT_RDONLY;
+       pmd_val(pmd) = (pmd_val(pmd) & ~mask) | (pgprot_val(newprot) & mask);
+       return pmd;
+}
+
+static inline void set_pmd(pmd_t *pmdp, pmd_t pmd)
+{
+       *pmdp = pmd;
+}

why this level of indirection?

Over manipulation in git :-), this can be scrubbed.

quoted

+
+static inline void set_pmd_at(struct mm_struct *mm, unsigned long addr,
+                             pmd_t *pmdp, pmd_t pmd)
+{
+       BUG_ON(addr >= TASK_SIZE);
+       pmd = __pmd(pmd_val(pmd) | PMD_SECT_nG);

why this side affect?

This replicates the side effect found when placing ptes into page tables. We
need the NG bit for user pages.

quoted

+       set_pmd(pmdp, pmd);
+       flush_pmd_entry(pmdp);
+}
+
+static inline int has_transparent_hugepage(void)
+{
+       return 1;
+}
+
 #endif /* __ASSEMBLY__ */

 #endif /* _ASM_PGTABLE_3LEVEL_H */

diff --git a/arch/arm/include/asm/pgtable.h b/arch/arm/include/asm/pgtable.h
index c35bf46..767aa7c 100644
--- a/arch/arm/include/asm/pgtable.h
+++ b/arch/arm/include/asm/pgtable.h

@@ -24,6 +24,9 @@
 #include <asm/memory.h>
 #include <asm/pgtable-hwdef.h>

+
+#include <asm/tlbflush.h>
+
 #ifdef CONFIG_ARM_LPAE
 #include <asm/pgtable-3level.h>
 #else

@@ -163,7 +166,6 @@ extern pgd_t swapper_pg_dir[PTRS_PER_PGD];
 #define pgd_offset_k(addr)     pgd_offset(&init_mm, addr)

 #define pmd_none(pmd)          (!pmd_val(pmd))
-#define pmd_present(pmd)       (pmd_val(pmd))

 static inline pte_t *pmd_page_vaddr(pmd_t pmd)
 {

diff --git a/arch/arm/include/asm/tlb.h b/arch/arm/include/asm/tlb.h
index 685e9e87..0fc2d9d 100644
--- a/arch/arm/include/asm/tlb.h
+++ b/arch/arm/include/asm/tlb.h

@@ -229,6 +229,12 @@ static inline void __pmd_free_tlb(struct mmu_gather *tlb, pmd_t *pmdp,
 #endif
 }

+static inline void
+tlb_remove_pmd_tlb_entry(struct mmu_gather *tlb, pmd_t *pmdp, unsigned long addr)
+{
+       tlb_add_flush(tlb, addr);
+}
+
 #define pte_free_tlb(tlb, ptep, addr)  __pte_free_tlb(tlb, ptep, addr)
 #define pmd_free_tlb(tlb, pmdp, addr)  __pmd_free_tlb(tlb, pmdp, addr)
 #define pud_free_tlb(tlb, pudp, addr)  pud_free((tlb)->mm, pudp)

diff --git a/arch/arm/include/asm/tlbflush.h b/arch/arm/include/asm/tlbflush.h
index 6e924d3..907cede 100644
--- a/arch/arm/include/asm/tlbflush.h
+++ b/arch/arm/include/asm/tlbflush.h

@@ -505,6 +505,8 @@ static inline void update_mmu_cache(struct vm_area_struct *vma,
 }
 #endif

+#define update_mmu_cache_pmd(vma, address, pmd) do { } while (0)
+
 #endif

 #endif /* CONFIG_MMU */

diff --git a/arch/arm/mm/fsr-3level.c b/arch/arm/mm/fsr-3level.c
index 05a4e94..47f4c6f 100644
--- a/arch/arm/mm/fsr-3level.c
+++ b/arch/arm/mm/fsr-3level.c

@@ -9,7 +9,7 @@ static struct fsr_info fsr_info[] = {
        { do_page_fault,        SIGSEGV, SEGV_MAPERR,   "level 3 translation fault"     },
        { do_bad,               SIGBUS,  0,             "reserved access flag fault"    },
        { do_bad,               SIGSEGV, SEGV_ACCERR,   "level 1 access flag fault"     },
-       { do_bad,               SIGSEGV, SEGV_ACCERR,   "level 2 access flag fault"     },
+       { do_page_fault,        SIGSEGV, SEGV_ACCERR,   "level 2 access flag fault"     },
        { do_page_fault,        SIGSEGV, SEGV_ACCERR,   "level 3 access flag fault"     },
        { do_bad,               SIGBUS,  0,             "reserved permission fault"     },
        { do_bad,               SIGSEGV, SEGV_ACCERR,   "level 1 permission fault"      },
--

1.7.9.5

Besides the nits it looks fine to me. I've done quite extensive
testing with varied workloads on this code over the last couple of
months on the vexpress TC2 and on the ARNDALE board using KVM/ARM with
huge pages, and it gives a nice ~15% performance increase on average
and is completely stable.

That's great to hear \o/.
Also I've found a decent perf boost when running tools like xz backed by huge pages.
(One can use the LD_PRELOAD mechanism in libhugetlbfs to make mallocs point to
huge pages).

-Christoffer