[PATCH 09/20] mm: Factor out functionality to finish page faults

[Jan Kara]

Introduce function finish_fault() as a helper function for finishing
page faults. It is rather thin wrapper around alloc_set_pte() but since
we'd want to call this from DAX code or filesystems, it is still useful
to avoid some boilerplate code.

Acked-by: Kirill A. Shutemov 
Reviewed-by: Ross Zwisler 
Signed-off-by: Jan Kara 
---
 include/linux/mm.h |  1 +
 mm/memory.c| 44 +++-
 2 files changed, 36 insertions(+), 9 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index 34d2891e9195..482455952f03 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -620,6 +620,7 @@ static inline pte_t maybe_mkwrite(pte_t pte, struct 
vm_area_struct *vma)
 
 int alloc_set_pte(struct vm_fault *vmf, struct mem_cgroup *memcg,
struct page *page);
+int finish_fault(struct vm_fault *vmf);
 #endif
 
 /*
diff --git a/mm/memory.c b/mm/memory.c
index 21a4a193a6c2..ba49e5bacf17 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3033,6 +3033,38 @@ int alloc_set_pte(struct vm_fault *vmf, struct 
mem_cgroup *memcg,
return 0;
 }
 
+
+/**
+ * finish_fault - finish page fault once we have prepared the page to fault
+ *
+ * @vmf: structure describing the fault
+ *
+ * This function handles all that is needed to finish a page fault once the
+ * page to fault in is prepared. It handles locking of PTEs, inserts PTE for
+ * given page, adds reverse page mapping, handles memcg charges and LRU
+ * addition. The function returns 0 on success, VM_FAULT_ code in case of
+ * error.
+ *
+ * The function expects the page to be locked and on success it consumes a
+ * reference of a page being mapped (for the PTE which maps it).
+ */
+int finish_fault(struct vm_fault *vmf)
+{
+   struct page *page;
+   int ret;
+
+   /* Did we COW the page? */
+   if ((vmf->flags & FAULT_FLAG_WRITE) &&
+   !(vmf->vma->vm_flags & VM_SHARED))
+   page = vmf->cow_page;
+   else
+   page = vmf->page;
+   ret = alloc_set_pte(vmf, vmf->memcg, page);
+   if (vmf->pte)
+   pte_unmap_unlock(vmf->pte, vmf->ptl);
+   return ret;
+}
+
 static unsigned long fault_around_bytes __read_mostly =
rounddown_pow_of_two(65536);
 
@@ -3178,9 +3210,7 @@ static int do_read_fault(struct vm_fault *vmf)
if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE | VM_FAULT_RETRY)))
return ret;
 
-   ret |= alloc_set_pte(vmf, NULL, vmf->page);
-   if (vmf->pte)
-   pte_unmap_unlock(vmf->pte, vmf->ptl);
+   ret |= finish_fault(vmf);
unlock_page(vmf->page);
if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE | VM_FAULT_RETRY)))
put_page(vmf->page);
@@ -3215,9 +3245,7 @@ static int do_cow_fault(struct vm_fault *vmf)
copy_user_highpage(vmf->cow_page, vmf->page, vmf->address, vma);
__SetPageUptodate(vmf->cow_page);
 
-   ret |= alloc_set_pte(vmf, vmf->memcg, vmf->cow_page);
-   if (vmf->pte)
-   pte_unmap_unlock(vmf->pte, vmf->ptl);
+   ret |= finish_fault(vmf);
if (!(ret & VM_FAULT_DAX_LOCKED)) {
unlock_page(vmf->page);
put_page(vmf->page);
@@ -3258,9 +3286,7 @@ static int do_shared_fault(struct vm_fault *vmf)
}
}
 
-   ret |= alloc_set_pte(vmf, NULL, vmf->page);
-   if (vmf->pte)
-   pte_unmap_unlock(vmf->pte, vmf->ptl);
+   ret |= finish_fault(vmf);
if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE |
VM_FAULT_RETRY))) {
unlock_page(vmf->page);
-- 
2.6.6

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Re: [PATCH 09/20] mm: Factor out functionality to finish page faults

[Jan Kara]

On Mon 17-10-16 11:40:42, Ross Zwisler wrote:
> On Tue, Sep 27, 2016 at 06:08:13PM +0200, Jan Kara wrote:
> > +   /* Did we COW the page? */
> > +   if (vmf->flags & FAULT_FLAG_WRITE && !(vmf->vma->vm_flags & VM_SHARED))
> 
> Oh, sorry, I did have one bit of feedback.  Maybe added parens around the flag
> check for readability:
> 
>   if ((vmf->flags & FAULT_FLAG_WRITE) && !(vmf->vma->vm_flags & 
> VM_SHARED))

Fixed.

> Aside from that one nit:
> 
> Reviewed-by: Ross Zwisler 

Thanks!

Honza 
-- 
Jan Kara 
SUSE Labs, CR
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Re: [PATCH 09/20] mm: Factor out functionality to finish page faults

[Ross Zwisler]

On Tue, Sep 27, 2016 at 06:08:13PM +0200, Jan Kara wrote:
> Introduce function finish_fault() as a helper function for finishing
> page faults. It is rather thin wrapper around alloc_set_pte() but since
> we'd want to call this from DAX code or filesystems, it is still useful
> to avoid some boilerplate code.
> 
> Signed-off-by: Jan Kara 
> ---

> diff --git a/mm/memory.c b/mm/memory.c
> index 17db88a38e8a..f54cfad7fe04 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -3029,6 +3029,36 @@ int alloc_set_pte(struct vm_fault *vmf, struct 
> mem_cgroup *memcg,
>   return 0;
>  }
>  
> +
> +/**
> + * finish_fault - finish page fault once we have prepared the page to fault
> + *
> + * @vmf: structure describing the fault
> + *
> + * This function handles all that is needed to finish a page fault once the
> + * page to fault in is prepared. It handles locking of PTEs, inserts PTE for
> + * given page, adds reverse page mapping, handles memcg charges and LRU
> + * addition. The function returns 0 on success, VM_FAULT_ code in case of
> + * error.
> + *
> + * The function expects the page to be locked.
> + */
> +int finish_fault(struct vm_fault *vmf)
> +{
> + struct page *page;
> + int ret;
> +
> + /* Did we COW the page? */
> + if (vmf->flags & FAULT_FLAG_WRITE && !(vmf->vma->vm_flags & VM_SHARED))

Oh, sorry, I did have one bit of feedback.  Maybe added parens around the flag
check for readability:

if ((vmf->flags & FAULT_FLAG_WRITE) && !(vmf->vma->vm_flags & 
VM_SHARED))

Aside from that one nit:

Reviewed-by: Ross Zwisler 

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Re: [PATCH 09/20] mm: Factor out functionality to finish page faults

[Ross Zwisler]

On Tue, Sep 27, 2016 at 06:08:13PM +0200, Jan Kara wrote:
> Introduce function finish_fault() as a helper function for finishing
> page faults. It is rather thin wrapper around alloc_set_pte() but since
> we'd want to call this from DAX code or filesystems, it is still useful
> to avoid some boilerplate code.
> 
> Signed-off-by: Jan Kara 

Reviewed-by: Ross Zwisler 
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[PATCH 09/20] mm: Factor out functionality to finish page faults

[Jan Kara]

Introduce function finish_fault() as a helper function for finishing
page faults. It is rather thin wrapper around alloc_set_pte() but since
we'd want to call this from DAX code or filesystems, it is still useful
to avoid some boilerplate code.

Signed-off-by: Jan Kara 
---
 include/linux/mm.h |  1 +
 mm/memory.c| 42 +-
 2 files changed, 34 insertions(+), 9 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index faa77b15e9a6..919ebdd27f1e 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -622,6 +622,7 @@ static inline pte_t maybe_mkwrite(pte_t pte, struct 
vm_area_struct *vma)
 
 int alloc_set_pte(struct vm_fault *vmf, struct mem_cgroup *memcg,
struct page *page);
+int finish_fault(struct vm_fault *vmf);
 #endif
 
 /*
diff --git a/mm/memory.c b/mm/memory.c
index 17db88a38e8a..f54cfad7fe04 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3029,6 +3029,36 @@ int alloc_set_pte(struct vm_fault *vmf, struct 
mem_cgroup *memcg,
return 0;
 }
 
+
+/**
+ * finish_fault - finish page fault once we have prepared the page to fault
+ *
+ * @vmf: structure describing the fault
+ *
+ * This function handles all that is needed to finish a page fault once the
+ * page to fault in is prepared. It handles locking of PTEs, inserts PTE for
+ * given page, adds reverse page mapping, handles memcg charges and LRU
+ * addition. The function returns 0 on success, VM_FAULT_ code in case of
+ * error.
+ *
+ * The function expects the page to be locked.
+ */
+int finish_fault(struct vm_fault *vmf)
+{
+   struct page *page;
+   int ret;
+
+   /* Did we COW the page? */
+   if (vmf->flags & FAULT_FLAG_WRITE && !(vmf->vma->vm_flags & VM_SHARED))
+   page = vmf->cow_page;
+   else
+   page = vmf->page;
+   ret = alloc_set_pte(vmf, vmf->memcg, page);
+   if (vmf->pte)
+   pte_unmap_unlock(vmf->pte, vmf->ptl);
+   return ret;
+}
+
 static unsigned long fault_around_bytes __read_mostly =
rounddown_pow_of_two(65536);
 
@@ -3174,9 +3204,7 @@ static int do_read_fault(struct vm_fault *vmf)
if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE | VM_FAULT_RETRY)))
return ret;
 
-   ret |= alloc_set_pte(vmf, NULL, vmf->page);
-   if (vmf->pte)
-   pte_unmap_unlock(vmf->pte, vmf->ptl);
+   ret |= finish_fault(vmf);
unlock_page(vmf->page);
if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE | VM_FAULT_RETRY)))
put_page(vmf->page);
@@ -3215,9 +3243,7 @@ static int do_cow_fault(struct vm_fault *vmf)
copy_user_highpage(new_page, vmf->page, vmf->address, vma);
__SetPageUptodate(new_page);
 
-   ret |= alloc_set_pte(vmf, memcg, new_page);
-   if (vmf->pte)
-   pte_unmap_unlock(vmf->pte, vmf->ptl);
+   ret |= finish_fault(vmf);
if (!(ret & VM_FAULT_DAX_LOCKED)) {
unlock_page(vmf->page);
put_page(vmf->page);
@@ -3258,9 +3284,7 @@ static int do_shared_fault(struct vm_fault *vmf)
}
}
 
-   ret |= alloc_set_pte(vmf, NULL, vmf->page);
-   if (vmf->pte)
-   pte_unmap_unlock(vmf->pte, vmf->ptl);
+   ret |= finish_fault(vmf);
if (unlikely(ret & (VM_FAULT_ERROR | VM_FAULT_NOPAGE |
VM_FAULT_RETRY))) {
unlock_page(vmf->page);
-- 
2.6.6

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