[PATCH 1/7] mm: infrastructure for page fault page caching

From: Josef Bacik
Date: Thu Oct 18 2018 - 16:23:34 EST

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We want to be able to cache the result of a previous loop of a page
fault in the case that we use VM_FAULT_RETRY, so introduce
handle_mm_fault_cacheable that will take a struct vm_fault directly, add
a ->cached_page field to vm_fault, and add helpers to init/cleanup the
struct vm_fault.

I've converted x86, other arch's can follow suit if they so wish, it's
relatively straightforward.

Signed-off-by: Josef Bacik <josef@xxxxxxxxxxxxxx>
---
arch/x86/mm/fault.c | 6 +++-
include/linux/mm.h | 31 +++++++++++++++++++++
mm/memory.c | 79 ++++++++++++++++++++++++++++++++---------------------
3 files changed, 84 insertions(+), 32 deletions(-)

diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
index 47bebfe6efa7..ef6e538c4931 100644
--- a/arch/x86/mm/fault.c
+++ b/arch/x86/mm/fault.c
@@ -1211,6 +1211,7 @@ static noinline void
__do_page_fault(struct pt_regs *regs, unsigned long error_code,
unsigned long address)
{
+ struct vm_fault vmf = {};
struct vm_area_struct *vma;
struct task_struct *tsk;
struct mm_struct *mm;
@@ -1392,7 +1393,8 @@ __do_page_fault(struct pt_regs *regs, unsigned long error_code,
* fault, so we read the pkey beforehand.
*/
pkey = vma_pkey(vma);
- fault = handle_mm_fault(vma, address, flags);
+ vm_fault_init(&vmf, vma, address, flags);
+ fault = handle_mm_fault_cacheable(&vmf);
major |= fault & VM_FAULT_MAJOR;

/*
@@ -1408,6 +1410,7 @@ __do_page_fault(struct pt_regs *regs, unsigned long error_code,
if (!fatal_signal_pending(tsk))
goto retry;
}
+ vm_fault_cleanup(&vmf);

/* User mode? Just return to handle the fatal exception */
if (flags & FAULT_FLAG_USER)
@@ -1418,6 +1421,7 @@ __do_page_fault(struct pt_regs *regs, unsigned long error_code,
return;
}

+ vm_fault_cleanup(&vmf);
up_read(&mm->mmap_sem);
if (unlikely(fault & VM_FAULT_ERROR)) {
mm_fault_error(regs, error_code, address, &pkey, fault);
diff --git a/include/linux/mm.h b/include/linux/mm.h
index a61ebe8ad4ca..4a84ec976dfc 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -360,6 +360,12 @@ struct vm_fault {
* is set (which is also implied by
* VM_FAULT_ERROR).
*/
+ struct page *cached_page; /* ->fault handlers that return
+ * VM_FAULT_RETRY can store their
+ * previous page here to be reused the
+ * next time we loop through the fault
+ * handler for faster lookup.
+ */
/* These three entries are valid only while holding ptl lock */
pte_t *pte; /* Pointer to pte entry matching
* the 'address'. NULL if the page
@@ -378,6 +384,16 @@ struct vm_fault {
*/
};

+static inline void vm_fault_init(struct vm_fault *vmf,
+ struct vm_area_struct *vma,
+ unsigned long address,
+ unsigned int flags)
+{
+ vmf->vma = vma;
+ vmf->address = address;
+ vmf->flags = flags;
+}
+
/* page entry size for vm->huge_fault() */
enum page_entry_size {
PE_SIZE_PTE = 0,
@@ -943,6 +959,14 @@ static inline void put_page(struct page *page)
__put_page(page);
}

+static inline void vm_fault_cleanup(struct vm_fault *vmf)
+{
+ if (vmf->cached_page) {
+ put_page(vmf->cached_page);
+ vmf->cached_page = NULL;
+ }
+}
+
#if defined(CONFIG_SPARSEMEM) && !defined(CONFIG_SPARSEMEM_VMEMMAP)
#define SECTION_IN_PAGE_FLAGS
#endif
@@ -1405,6 +1429,7 @@ int invalidate_inode_page(struct page *page);
#ifdef CONFIG_MMU
extern vm_fault_t handle_mm_fault(struct vm_area_struct *vma,
unsigned long address, unsigned int flags);
+extern vm_fault_t handle_mm_fault_cacheable(struct vm_fault *vmf);
extern int fixup_user_fault(struct task_struct *tsk, struct mm_struct *mm,
unsigned long address, unsigned int fault_flags,
bool *unlocked);
@@ -1420,6 +1445,12 @@ static inline vm_fault_t handle_mm_fault(struct vm_area_struct *vma,
BUG();
return VM_FAULT_SIGBUS;
}
+static inline vm_fault_t handle_mm_fault_cacheable(struct vm_fault *vmf)
+{
+ /* should never happen if there's no MMU */
+ BUG();
+ return VM_FAULT_SIGBUS;
+}
static inline int fixup_user_fault(struct task_struct *tsk,
struct mm_struct *mm, unsigned long address,
unsigned int fault_flags, bool *unlocked)
diff --git a/mm/memory.c b/mm/memory.c
index c467102a5cbc..433075f722ea 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -4024,36 +4024,34 @@ static vm_fault_t handle_pte_fault(struct vm_fault *vmf)
* The mmap_sem may have been released depending on flags and our
* return value. See filemap_fault() and __lock_page_or_retry().
*/
-static vm_fault_t __handle_mm_fault(struct vm_area_struct *vma,
- unsigned long address, unsigned int flags)
+static vm_fault_t __handle_mm_fault(struct vm_fault *vmf)
{
- struct vm_fault vmf = {
- .vma = vma,
- .address = address & PAGE_MASK,
- .flags = flags,
- .pgoff = linear_page_index(vma, address),
- .gfp_mask = __get_fault_gfp_mask(vma),
- };
- unsigned int dirty = flags & FAULT_FLAG_WRITE;
+ struct vm_area_struct *vma = vmf->vma;
+ unsigned long address = vmf->address;
+ unsigned int dirty = vmf->flags & FAULT_FLAG_WRITE;
struct mm_struct *mm = vma->vm_mm;
pgd_t *pgd;
p4d_t *p4d;
vm_fault_t ret;

+ vmf->address = address & PAGE_MASK;
+ vmf->pgoff = linear_page_index(vma, address);
+ vmf->gfp_mask = __get_fault_gfp_mask(vma);
+
pgd = pgd_offset(mm, address);
p4d = p4d_alloc(mm, pgd, address);
if (!p4d)
return VM_FAULT_OOM;

- vmf.pud = pud_alloc(mm, p4d, address);
- if (!vmf.pud)
+ vmf->pud = pud_alloc(mm, p4d, address);
+ if (!vmf->pud)
return VM_FAULT_OOM;
- if (pud_none(*vmf.pud) && transparent_hugepage_enabled(vma)) {
- ret = create_huge_pud(&vmf);
+ if (pud_none(*vmf->pud) && transparent_hugepage_enabled(vma)) {
+ ret = create_huge_pud(vmf);
if (!(ret & VM_FAULT_FALLBACK))
return ret;
} else {
- pud_t orig_pud = *vmf.pud;
+ pud_t orig_pud = *vmf->pud;

barrier();
if (pud_trans_huge(orig_pud) || pud_devmap(orig_pud)) {
@@ -4061,50 +4059,50 @@ static vm_fault_t __handle_mm_fault(struct vm_area_struct *vma,
/* NUMA case for anonymous PUDs would go here */

if (dirty && !pud_write(orig_pud)) {
- ret = wp_huge_pud(&vmf, orig_pud);
+ ret = wp_huge_pud(vmf, orig_pud);
if (!(ret & VM_FAULT_FALLBACK))
return ret;
} else {
- huge_pud_set_accessed(&vmf, orig_pud);
+ huge_pud_set_accessed(vmf, orig_pud);
return 0;
}
}
}

- vmf.pmd = pmd_alloc(mm, vmf.pud, address);
- if (!vmf.pmd)
+ vmf->pmd = pmd_alloc(mm, vmf->pud, address);
+ if (!vmf->pmd)
return VM_FAULT_OOM;
- if (pmd_none(*vmf.pmd) && transparent_hugepage_enabled(vma)) {
- ret = create_huge_pmd(&vmf);
+ if (pmd_none(*vmf->pmd) && transparent_hugepage_enabled(vma)) {
+ ret = create_huge_pmd(vmf);
if (!(ret & VM_FAULT_FALLBACK))
return ret;
} else {
- pmd_t orig_pmd = *vmf.pmd;
+ pmd_t orig_pmd = *vmf->pmd;

barrier();
if (unlikely(is_swap_pmd(orig_pmd))) {
VM_BUG_ON(thp_migration_supported() &&
!is_pmd_migration_entry(orig_pmd));
if (is_pmd_migration_entry(orig_pmd))
- pmd_migration_entry_wait(mm, vmf.pmd);
+ pmd_migration_entry_wait(mm, vmf->pmd);
return 0;
}
if (pmd_trans_huge(orig_pmd) || pmd_devmap(orig_pmd)) {
if (pmd_protnone(orig_pmd) && vma_is_accessible(vma))
- return do_huge_pmd_numa_page(&vmf, orig_pmd);
+ return do_huge_pmd_numa_page(vmf, orig_pmd);

if (dirty && !pmd_write(orig_pmd)) {
- ret = wp_huge_pmd(&vmf, orig_pmd);
+ ret = wp_huge_pmd(vmf, orig_pmd);
if (!(ret & VM_FAULT_FALLBACK))
return ret;
} else {
- huge_pmd_set_accessed(&vmf, orig_pmd);
+ huge_pmd_set_accessed(vmf, orig_pmd);
return 0;
}
}
}

- return handle_pte_fault(&vmf);
+ return handle_pte_fault(vmf);
}

/*
@@ -4113,9 +4111,10 @@ static vm_fault_t __handle_mm_fault(struct vm_area_struct *vma,
* The mmap_sem may have been released depending on flags and our
* return value. See filemap_fault() and __lock_page_or_retry().
*/
-vm_fault_t handle_mm_fault(struct vm_area_struct *vma, unsigned long address,
- unsigned int flags)
+static vm_fault_t do_handle_mm_fault(struct vm_fault *vmf)
{
+ struct vm_area_struct *vma = vmf->vma;
+ unsigned int flags = vmf->flags;
vm_fault_t ret;

__set_current_state(TASK_RUNNING);
@@ -4139,9 +4138,9 @@ vm_fault_t handle_mm_fault(struct vm_area_struct *vma, unsigned long address,
mem_cgroup_enter_user_fault();

if (unlikely(is_vm_hugetlb_page(vma)))
- ret = hugetlb_fault(vma->vm_mm, vma, address, flags);
+ ret = hugetlb_fault(vma->vm_mm, vma, vmf->address, flags);
else
- ret = __handle_mm_fault(vma, address, flags);
+ ret = __handle_mm_fault(vmf);

if (flags & FAULT_FLAG_USER) {
mem_cgroup_exit_user_fault();
@@ -4157,8 +4156,26 @@ vm_fault_t handle_mm_fault(struct vm_area_struct *vma, unsigned long address,

return ret;
}
+
+vm_fault_t handle_mm_fault(struct vm_area_struct *vma, unsigned long address,
+ unsigned int flags)
+{
+ struct vm_fault vmf = {};
+ vm_fault_t ret;
+
+ vm_fault_init(&vmf, vma, address, flags);
+ ret = do_handle_mm_fault(&vmf);
+ vm_fault_cleanup(&vmf);
+ return ret;
+}
EXPORT_SYMBOL_GPL(handle_mm_fault);

+vm_fault_t handle_mm_fault_cacheable(struct vm_fault *vmf)
+{
+ return do_handle_mm_fault(vmf);
+}
+EXPORT_SYMBOL_GPL(handle_mm_fault_cacheable);
+
#ifndef __PAGETABLE_P4D_FOLDED
/*
* Allocate p4d page table.
--
2.14.3

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