Re: [x86 PAT PATCH 2/2] mm, x86, PAT: rework linear pfn-mmap tracking

Konstantin Khlebnikov <khlebnikov@xxxxxxxxxx> · Tue, 03 Apr 2012 09:55:21 +0400

Konstantin Khlebnikov wrote:
Suresh Siddha wrote:
From: Konstantin Khlebnikov<khlebnikov@xxxxxxxxxx>

This patch replaces generic vma-flag VM_PFN_AT_MMAP with x86-only VM_PAT.

We can toss mapping address from remap_pfn_range() into track_pfn_vma_new(),
and collect all PAT-related logic together in arch/x86/.

This patch also restores orignal frustration-free is_cow_mapping() check in
remap_pfn_range(), as it was before commit v2.6.28-rc8-88-g3c8bb73
("x86: PAT: store vm_pgoff for all linear_over_vma_region mappings - v3")

is_linear_pfn_mapping() checks can be removed from mm/huge_memory.c,
because it already handled by VM_PFNMAP in VM_NO_THP bit-mask.

Signed-off-by: Konstantin Khlebnikov<khlebnikov@xxxxxxxxxx>
Signed-off-by: Suresh Siddha<suresh.b.siddha@xxxxxxxxx>
Cc: Venkatesh Pallipadi<venki@xxxxxxxxxx>
Cc: H. Peter Anvin<hpa@xxxxxxxxx>
Cc: Nick Piggin<npiggin@xxxxxxx>
Cc: Ingo Molnar<mingo@xxxxxxxxxx>
---
   arch/x86/mm/pat.c             |   16 +++++++++++-----
   include/asm-generic/pgtable.h |    4 ++--
   include/linux/mm.h            |   15 +--------------
   mm/huge_memory.c              |    7 +++----
   mm/memory.c                   |   15 ++++++++-------
   5 files changed, 25 insertions(+), 32 deletions(-)

diff --git a/arch/x86/mm/pat.c b/arch/x86/mm/pat.c
index 617f42b..cde7e19 100644
--- a/arch/x86/mm/pat.c
+++ b/arch/x86/mm/pat.c
@@ -665,7 +665,7 @@ int track_pfn_vma_copy(struct vm_area_struct *vma)
       unsigned long vma_size = vma->vm_end - vma->vm_start;
       pgprot_t pgprot;

-     if (is_linear_pfn_mapping(vma)) {
+     if (vma->vm_flags&   VM_PAT) {
               /*
                * reserve the whole chunk covered by vma. We need the
                * starting address and protection from pte.
@@ -690,13 +690,19 @@ int track_pfn_vma_copy(struct vm_area_struct *vma)
    * single reserve_pfn_range call.
    */
   int track_pfn_vma_new(struct vm_area_struct *vma, pgprot_t *prot,
-                     unsigned long pfn, unsigned long size)
+                   unsigned long addr, unsigned long pfn, unsigned long size)
   {
       unsigned long flags;

       /* reserve the whole chunk starting from pfn */
-     if (is_linear_pfn_mapping(vma))
-             return reserve_pfn_range(pfn, size, prot, 0);
+     if (addr == vma->vm_start&&   size == (vma->vm_end - vma->vm_start)) {
+             int ret;
+
+             ret = reserve_pfn_range(pfn, size, prot, 0);
+             if (!ret)
+                     vma->vm_flags |= VM_PAT;
+             return ret;
+     }

       if (!pat_enabled)
               return 0;
@@ -720,7 +726,7 @@ void untrack_pfn_vma(struct vm_area_struct *vma, unsigned long pfn,
       resource_size_t paddr;
       unsigned long prot;

-     if (!is_linear_pfn_mapping(vma))
+     if (!(vma->vm_flags&   VM_PAT))
               return;

       /* free the chunk starting from pfn or the whole chunk */
diff --git a/include/asm-generic/pgtable.h b/include/asm-generic/pgtable.h
index 125c54e..688a2a5 100644
--- a/include/asm-generic/pgtable.h
+++ b/include/asm-generic/pgtable.h
@@ -389,7 +389,7 @@ static inline void ptep_modify_prot_commit(struct mm_struct *mm,
    * for physical range indicated by pfn and size.
    */
   static inline int track_pfn_vma_new(struct vm_area_struct *vma, pgprot_t *prot,
-                                     unsigned long pfn, unsigned long size)
+             unsigned long pfn, unsigned long addr, unsigned long size)
   {
       return 0;
   }
@@ -420,7 +420,7 @@ static inline void untrack_pfn_vma(struct vm_area_struct *vma,
   }
   #else
   extern int track_pfn_vma_new(struct vm_area_struct *vma, pgprot_t *prot,
-                             unsigned long pfn, unsigned long size);
+             unsigned long pfn, unsigned long addr, unsigned long size);
   extern int track_pfn_vma_copy(struct vm_area_struct *vma);
   extern void untrack_pfn_vma(struct vm_area_struct *vma, unsigned long pfn,
                               unsigned long size);
diff --git a/include/linux/mm.h b/include/linux/mm.h
index d8738a4..b8e5fe5 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -117,7 +117,7 @@ extern unsigned int kobjsize(const void *objp);
   #define VM_CAN_NONLINEAR 0x08000000 /* Has ->fault&   does nonlinear pages */
   #define VM_MIXEDMAP 0x10000000      /* Can contain "struct page" and pure PFN pages */
   #define VM_SAO              0x20000000      /* Strong Access Ordering (powerpc) */
-#define VM_PFN_AT_MMAP       0x40000000      /* PFNMAP vma that is fully mapped at mmap time */
+#define VM_PAT               0x40000000      /* PAT reserves whole VMA at once (x86) */
   #define VM_MERGEABLE        0x80000000      /* KSM may merge identical pages */

   /* Bits set in the VMA until the stack is in its final location */
@@ -158,19 +158,6 @@ extern pgprot_t protection_map[16];
   #define FAULT_FLAG_RETRY_NOWAIT     0x10    /* Don't drop mmap_sem and wait when retrying */
   #define FAULT_FLAG_KILLABLE 0x20    /* The fault task is in SIGKILL killable region */

-/*
- * This interface is used by x86 PAT code to identify a pfn mapping that is
- * linear over entire vma. This is to optimize PAT code that deals with
- * marking the physical region with a particular prot. This is not for generic
- * mm use. Note also that this check will not work if the pfn mapping is
- * linear for a vma starting at physical address 0. In which case PAT code
- * falls back to slow path of reserving physical range page by page.
- */
-static inline int is_linear_pfn_mapping(struct vm_area_struct *vma)
-{
-     return !!(vma->vm_flags&   VM_PFN_AT_MMAP);
-}
-
   static inline int is_pfn_mapping(struct vm_area_struct *vma)
   {
       return !!(vma->vm_flags&   VM_PFNMAP);
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index f0e5306..cf827da 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1650,7 +1650,7 @@ int khugepaged_enter_vma_merge(struct vm_area_struct *vma)
        * If is_pfn_mapping() is true is_learn_pfn_mapping() must be
        * true too, verify it here.
        */
-     VM_BUG_ON(is_linear_pfn_mapping(vma) || vma->vm_flags&   VM_NO_THP);
+     VM_BUG_ON(vma->vm_flags&   VM_NO_THP);
       hstart = (vma->vm_start + ~HPAGE_PMD_MASK)&   HPAGE_PMD_MASK;
       hend = vma->vm_end&   HPAGE_PMD_MASK;
       if (hstart<   hend)
@@ -1908,7 +1908,7 @@ static void collapse_huge_page(struct mm_struct *mm,
        * If is_pfn_mapping() is true is_learn_pfn_mapping() must be
        * true too, verify it here.
        */
-     VM_BUG_ON(is_linear_pfn_mapping(vma) || vma->vm_flags&   VM_NO_THP);
+     VM_BUG_ON(vma->vm_flags&   VM_NO_THP);

       pgd = pgd_offset(mm, address);
       if (!pgd_present(*pgd))
@@ -2150,8 +2150,7 @@ static unsigned int khugepaged_scan_mm_slot(unsigned int pages,
                * If is_pfn_mapping() is true is_learn_pfn_mapping()
                * must be true too, verify it here.
                */
-             VM_BUG_ON(is_linear_pfn_mapping(vma) ||
-                       vma->vm_flags&   VM_NO_THP);
+             VM_BUG_ON(vma->vm_flags&   VM_NO_THP);

               hstart = (vma->vm_start + ~HPAGE_PMD_MASK)&   HPAGE_PMD_MASK;
               hend = vma->vm_end&   HPAGE_PMD_MASK;
diff --git a/mm/memory.c b/mm/memory.c
index 6105f47..e6e4dfd 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -2145,7 +2145,7 @@ int vm_insert_pfn(struct vm_area_struct *vma, unsigned long addr,

       if (addr<   vma->vm_start || addr>= vma->vm_end)
               return -EFAULT;
-     if (track_pfn_vma_new(vma,&pgprot, pfn, PAGE_SIZE))
+     if (track_pfn_vma_new(vma,&pgprot, pfn, addr, PAGE_SIZE))
               return -EINVAL;

Old code does not uses PAT for vm_insert_pfn, now it can use it for single-page vma.
And I see glitches on my notebook if kernel do this (see comment in v2 of my patch)

Probably we shouldn't touch this, plus seems like using pat-engine for single page isn't optimal:
it allocates special control structures for this.

Ignore this, I didn't see comment in 0/2 mail



       ret = insert_pfn(vma, addr, pfn, pgprot);
@@ -2285,23 +2285,24 @@ int remap_pfn_range(struct vm_area_struct *vma, unsigned long addr,
        * There's a horrible special case to handle copy-on-write
        * behaviour that some programs depend on. We mark the "original"
        * un-COW'ed pages by matching them up with "vma->vm_pgoff".
+      * See vm_normal_page() for details.
        */
-     if (addr == vma->vm_start&&   end == vma->vm_end) {
+
+     if (is_cow_mapping(vma->vm_flags)) {
+             if (addr != vma->vm_start || end != vma->vm_end)
+                     return -EINVAL;
               vma->vm_pgoff = pfn;
-             vma->vm_flags |= VM_PFN_AT_MMAP;
-     } else if (is_cow_mapping(vma->vm_flags))
-             return -EINVAL;
+     }

       vma->vm_flags |= VM_IO | VM_RESERVED | VM_PFNMAP;

-     err = track_pfn_vma_new(vma,&prot, pfn, PAGE_ALIGN(size));
+     err = track_pfn_vma_new(vma,&prot, pfn, addr, PAGE_ALIGN(size));
       if (err) {
               /*
                * To indicate that track_pfn related cleanup is not
                * needed from higher level routine calling unmap_vmas
                */
               vma->vm_flags&= ~(VM_IO | VM_RESERVED | VM_PFNMAP);
-             vma->vm_flags&= ~VM_PFN_AT_MMAP;
               return -EINVAL;
       }


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