[PATCH 0/4] Cleanup mm_populate() codepath

[PATCH 0/4] Cleanup mm_populate() codepath

[Kirill A. Shutemov]

While reading mlock()- and mm_populate()-related code, I've found several
things confusing. This patchset cleanup the codepath for future readers.

Kirill A. Shutemov (4):
  mm: rename FOLL_MLOCK to FOLL_POPULATE
  mm: rename __mlock_vma_pages_range() to populate_vma_page_range()
  mm: move gup() -> posix mlock() error conversion out of __mm_populate
  mm: move mm_populate()-related code to mm/gup.c

 Documentation/vm/unevictable-lru.txt |  26 +++----
 include/linux/mm.h                   |   2 +-
 mm/gup.c                             | 124 ++++++++++++++++++++++++++++++++-
 mm/huge_memory.c                     |   2 +-
 mm/internal.h                        |   2 +-
 mm/mlock.c                           | 131 +++--------------------------------
 mm/mmap.c                            |   4 +-
 7 files changed, 142 insertions(+), 149 deletions(-)

-- 
2.1.4

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[PATCH 1/4] mm: rename FOLL_MLOCK to FOLL_POPULATE

[Kirill A. Shutemov]

After commit a1fde08c74e9 FOLL_MLOCK has lost its original meaning: we
don't necessary mlock the page if the flags is set -- we also take
VM_LOCKED into consideration.

Since we use the same codepath for __mm_populate(), let's rename
FOLL_MLOCK to FOLL_POPULATE.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Michel Lespinasse <walken@google.com>
---
 include/linux/mm.h | 2 +-
 mm/gup.c           | 6 +++---
 mm/huge_memory.c   | 2 +-
 mm/mlock.c         | 2 +-
 4 files changed, 6 insertions(+), 6 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index a09837f3f4b7..2dbf6f0f6e5b 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -2110,7 +2110,7 @@ static inline struct page *follow_page(struct vm_area_struct *vma,
 #define FOLL_FORCE	0x10	/* get_user_pages read/write w/o permission */
 #define FOLL_NOWAIT	0x20	/* if a disk transfer is needed, start the IO
 				 * and return without waiting upon it */
-#define FOLL_MLOCK	0x40	/* mark page as mlocked */
+#define FOLL_POPULATE	0x40	/* fault in page */
 #define FOLL_SPLIT	0x80	/* don't return transhuge pages, split them */
 #define FOLL_HWPOISON	0x100	/* check page is hwpoisoned */
 #define FOLL_NUMA	0x200	/* force NUMA hinting page fault */
diff --git a/mm/gup.c b/mm/gup.c
index a6e24e246f86..1b114ba9aebf 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -92,7 +92,7 @@ retry:
 		 */
 		mark_page_accessed(page);
 	}
-	if ((flags & FOLL_MLOCK) && (vma->vm_flags & VM_LOCKED)) {
+	if ((flags & FOLL_POPULATE) && (vma->vm_flags & VM_LOCKED)) {
 		/*
 		 * The preliminary mapping check is mainly to avoid the
 		 * pointless overhead of lock_page on the ZERO_PAGE
@@ -265,8 +265,8 @@ static int faultin_page(struct task_struct *tsk, struct vm_area_struct *vma,
 	unsigned int fault_flags = 0;
 	int ret;
 
-	/* For mlock, just skip the stack guard page. */
-	if ((*flags & FOLL_MLOCK) &&
+	/* For mm_populate(), just skip the stack guard page. */
+	if ((*flags & FOLL_POPULATE) &&
 			(stack_guard_page_start(vma, address) ||
 			 stack_guard_page_end(vma, address + PAGE_SIZE)))
 		return -ENOENT;
diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index e08e37ad050e..bc8d351026a9 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -1231,7 +1231,7 @@ struct page *follow_trans_huge_pmd(struct vm_area_struct *vma,
 					  pmd, _pmd,  1))
 			update_mmu_cache_pmd(vma, addr, pmd);
 	}
-	if ((flags & FOLL_MLOCK) && (vma->vm_flags & VM_LOCKED)) {
+	if ((flags & FOLL_POPULATE) && (vma->vm_flags & VM_LOCKED)) {
 		if (page->mapping && trylock_page(page)) {
 			lru_add_drain();
 			if (page->mapping)
diff --git a/mm/mlock.c b/mm/mlock.c
index 73cf0987088c..7712d8ab6fe5 100644
--- a/mm/mlock.c
+++ b/mm/mlock.c
@@ -237,7 +237,7 @@ long __mlock_vma_pages_range(struct vm_area_struct *vma,
 	VM_BUG_ON_VMA(end   > vma->vm_end, vma);
 	VM_BUG_ON_MM(!rwsem_is_locked(&mm->mmap_sem), mm);
 
-	gup_flags = FOLL_TOUCH | FOLL_MLOCK;
+	gup_flags = FOLL_TOUCH | FOLL_POPULATE;
 	/*
 	 * We want to touch writable mappings with a write fault in order
 	 * to break COW, except for shared mappings because these don't COW
-- 
2.1.4

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Re: [PATCH 1/4] mm: rename FOLL_MLOCK to FOLL_POPULATE

[David Rientjes]

On Wed, 11 Feb 2015, Kirill A. Shutemov wrote:

> After commit a1fde08c74e9 FOLL_MLOCK has lost its original meaning: we
> don't necessary mlock the page if the flags is set -- we also take
> VM_LOCKED into consideration.
> 

s/necessary/necessarily/

> Since we use the same codepath for __mm_populate(), let's rename
> FOLL_MLOCK to FOLL_POPULATE.
> 
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>

Acked-by: David Rientjes <rientjes@google.com>

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[PATCH 2/4] mm: rename __mlock_vma_pages_range() to populate_vma_page_range()

[Kirill A. Shutemov]

__mlock_vma_pages_range() doesn't necessary mlock pages. It depends on
vma flags. The same codepath is used for MAP_POPULATE.

Let's rename __mlock_vma_pages_range() to populate_vma_page_range().

This patch also drops mlock_vma_pages_range() references from
documentation. It has gone in commit cea10a19b797.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Michel Lespinasse <walken@google.com>
---
 Documentation/vm/unevictable-lru.txt | 26 ++++++++------------------
 mm/internal.h                        |  2 +-
 mm/mlock.c                           | 12 ++++++------
 mm/mmap.c                            |  4 ++--
 4 files changed, 17 insertions(+), 27 deletions(-)

diff --git a/Documentation/vm/unevictable-lru.txt b/Documentation/vm/unevictable-lru.txt
index 744f82f86c58..86cb4624fc5a 100644
--- a/Documentation/vm/unevictable-lru.txt
+++ b/Documentation/vm/unevictable-lru.txt
@@ -317,7 +317,7 @@ If the VMA passes some filtering as described in "Filtering Special Vmas"
 below, mlock_fixup() will attempt to merge the VMA with its neighbors or split
 off a subset of the VMA if the range does not cover the entire VMA.  Once the
 VMA has been merged or split or neither, mlock_fixup() will call
-__mlock_vma_pages_range() to fault in the pages via get_user_pages() and to
+populate_vma_page_range() to fault in the pages via get_user_pages() and to
 mark the pages as mlocked via mlock_vma_page().
 
 Note that the VMA being mlocked might be mapped with PROT_NONE.  In this case,
@@ -327,7 +327,7 @@ fault path or in vmscan.
 
 Also note that a page returned by get_user_pages() could be truncated or
 migrated out from under us, while we're trying to mlock it.  To detect this,
-__mlock_vma_pages_range() checks page_mapping() after acquiring the page lock.
+populate_vma_page_range() checks page_mapping() after acquiring the page lock.
 If the page is still associated with its mapping, we'll go ahead and call
 mlock_vma_page().  If the mapping is gone, we just unlock the page and move on.
 In the worst case, this will result in a page mapped in a VM_LOCKED VMA
@@ -392,7 +392,7 @@ ignored for munlock.
 
 If the VMA is VM_LOCKED, mlock_fixup() again attempts to merge or split off the
 specified range.  The range is then munlocked via the function
-__mlock_vma_pages_range() - the same function used to mlock a VMA range -
+populate_vma_page_range() - the same function used to mlock a VMA range -
 passing a flag to indicate that munlock() is being performed.
 
 Because the VMA access protections could have been changed to PROT_NONE after
@@ -402,7 +402,7 @@ get_user_pages() was enhanced to accept a flag to ignore the permissions when
 fetching the pages - all of which should be resident as a result of previous
 mlocking.
 
-For munlock(), __mlock_vma_pages_range() unlocks individual pages by calling
+For munlock(), populate_vma_page_range() unlocks individual pages by calling
 munlock_vma_page().  munlock_vma_page() unconditionally clears the PG_mlocked
 flag using TestClearPageMlocked().  As with mlock_vma_page(),
 munlock_vma_page() use the Test*PageMlocked() function to handle the case where
@@ -463,21 +463,11 @@ populate the page table.
 
 To mlock a range of memory under the unevictable/mlock infrastructure, the
 mmap() handler and task address space expansion functions call
-mlock_vma_pages_range() specifying the vma and the address range to mlock.
-mlock_vma_pages_range() filters VMAs like mlock_fixup(), as described above in
-"Filtering Special VMAs".  It will clear the VM_LOCKED flag, which will have
-already been set by the caller, in filtered VMAs.  Thus these VMA's need not be
-visited for munlock when the region is unmapped.
-
-For "normal" VMAs, mlock_vma_pages_range() calls __mlock_vma_pages_range() to
-fault/allocate the pages and mlock them.  Again, like mlock_fixup(),
-mlock_vma_pages_range() downgrades the mmap semaphore to read mode before
-attempting to fault/allocate and mlock the pages and "upgrades" the semaphore
-back to write mode before returning.
-
-The callers of mlock_vma_pages_range() will have already added the memory range
+populate_vma_page_range() specifying the vma and the address range to mlock.
+
+The callers of populate_vma_page_range() will have already added the memory range
 to be mlocked to the task's "locked_vm".  To account for filtered VMAs,
-mlock_vma_pages_range() returns the number of pages NOT mlocked.  All of the
+populate_vma_page_range() returns the number of pages NOT mlocked.  All of the
 callers then subtract a non-negative return value from the task's locked_vm.  A
 negative return value represent an error - for example, from get_user_pages()
 attempting to fault in a VMA with PROT_NONE access.  In this case, we leave the
diff --git a/mm/internal.h b/mm/internal.h
index c4d6c9b43491..5445860bfc08 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -240,7 +240,7 @@ void __vma_link_list(struct mm_struct *mm, struct vm_area_struct *vma,
 		struct vm_area_struct *prev, struct rb_node *rb_parent);
 
 #ifdef CONFIG_MMU
-extern long __mlock_vma_pages_range(struct vm_area_struct *vma,
+extern long populate_vma_page_range(struct vm_area_struct *vma,
 		unsigned long start, unsigned long end, int *nonblocking);
 extern void munlock_vma_pages_range(struct vm_area_struct *vma,
 			unsigned long start, unsigned long end);
diff --git a/mm/mlock.c b/mm/mlock.c
index 7712d8ab6fe5..c3ea18323034 100644
--- a/mm/mlock.c
+++ b/mm/mlock.c
@@ -206,13 +206,13 @@ out:
 }
 
 /**
- * __mlock_vma_pages_range() -  mlock a range of pages in the vma.
+ * populate_vma_page_range() -  populate a range of pages in the vma.
  * @vma:   target vma
  * @start: start address
  * @end:   end address
  * @nonblocking:
  *
- * This takes care of making the pages present too.
+ * This takes care of mlocking the pages too if VM_LOCKED is set.
  *
  * return 0 on success, negative error code on error.
  *
@@ -224,7 +224,7 @@ out:
  * If @nonblocking is non-NULL, it must held for read only and may be
  * released.  If it's released, *@nonblocking will be set to 0.
  */
-long __mlock_vma_pages_range(struct vm_area_struct *vma,
+long populate_vma_page_range(struct vm_area_struct *vma,
 		unsigned long start, unsigned long end, int *nonblocking)
 {
 	struct mm_struct *mm = vma->vm_mm;
@@ -596,7 +596,7 @@ success:
 	/*
 	 * vm_flags is protected by the mmap_sem held in write mode.
 	 * It's okay if try_to_unmap_one unmaps a page just after we
-	 * set VM_LOCKED, __mlock_vma_pages_range will bring it back.
+	 * set VM_LOCKED, populate_vma_page_range will bring it back.
 	 */
 
 	if (lock)
@@ -702,11 +702,11 @@ int __mm_populate(unsigned long start, unsigned long len, int ignore_errors)
 		if (nstart < vma->vm_start)
 			nstart = vma->vm_start;
 		/*
-		 * Now fault in a range of pages. __mlock_vma_pages_range()
+		 * Now fault in a range of pages. populate_vma_page_range()
 		 * double checks the vma flags, so that it won't mlock pages
 		 * if the vma was already munlocked.
 		 */
-		ret = __mlock_vma_pages_range(vma, nstart, nend, &locked);
+		ret = populate_vma_page_range(vma, nstart, nend, &locked);
 		if (ret < 0) {
 			if (ignore_errors) {
 				ret = 0;
diff --git a/mm/mmap.c b/mm/mmap.c
index da9990acc08b..943c6ad18b1d 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -2318,7 +2318,7 @@ find_extend_vma(struct mm_struct *mm, unsigned long addr)
 	if (!prev || expand_stack(prev, addr))
 		return NULL;
 	if (prev->vm_flags & VM_LOCKED)
-		__mlock_vma_pages_range(prev, addr, prev->vm_end, NULL);
+		populate_vma_page_range(prev, addr, prev->vm_end, NULL);
 	return prev;
 }
 #else
@@ -2353,7 +2353,7 @@ find_extend_vma(struct mm_struct *mm, unsigned long addr)
 	if (expand_stack(vma, addr))
 		return NULL;
 	if (vma->vm_flags & VM_LOCKED)
-		__mlock_vma_pages_range(vma, addr, start, NULL);
+		populate_vma_page_range(vma, addr, start, NULL);
 	return vma;
 }
 #endif
-- 
2.1.4

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Re: [PATCH 2/4] mm: rename __mlock_vma_pages_range() to populate_vma_page_range()

[David Rientjes]

On Wed, 11 Feb 2015, Kirill A. Shutemov wrote:

> __mlock_vma_pages_range() doesn't necessary mlock pages. It depends on
> vma flags. The same codepath is used for MAP_POPULATE.
> 

s/necessary/necessarily/

> Let's rename __mlock_vma_pages_range() to populate_vma_page_range().
> 
> This patch also drops mlock_vma_pages_range() references from
> documentation. It has gone in commit cea10a19b797.
> 
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>

I think it makes sense to drop the references about "downgrading" 
mm->mmap_sem in the documentation since populate_vma_page_range() can be 
called with it held either for read or write depending on the context.

Acked-by: David Rientjes <rientjes@google.com>

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Re: [PATCH 2/4] mm: rename __mlock_vma_pages_range() to populate_vma_page_range()

[Kirill A. Shutemov]

On Wed, Feb 11, 2015 at 11:59:33AM -0800, David Rientjes wrote:
> On Wed, 11 Feb 2015, Kirill A. Shutemov wrote:
> 
> > __mlock_vma_pages_range() doesn't necessary mlock pages. It depends on
> > vma flags. The same codepath is used for MAP_POPULATE.
> > 
> 
> s/necessary/necessarily/
> 
> > Let's rename __mlock_vma_pages_range() to populate_vma_page_range().
> > 
> > This patch also drops mlock_vma_pages_range() references from
> > documentation. It has gone in commit cea10a19b797.
> > 
> > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> 
> I think it makes sense to drop the references about "downgrading" 
> mm->mmap_sem in the documentation since populate_vma_page_range() can be 
> called with it held either for read or write depending on the context.

I'm not sure what references you're talking about.

Is it about this part:

 * If @nonblocking is non-NULL, it must held for read only and may be
 * released.  If it's released, *@nonblocking will be set to 0.

?

The comment is still true as far as I can say. It comes from up_read() in
__lock_page_or_retry().

-- 
 Kirill A. Shutemov

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Re: [PATCH 2/4] mm: rename __mlock_vma_pages_range() to populate_vma_page_range()

[David Rientjes]

On Thu, 12 Feb 2015, Kirill A. Shutemov wrote:

> > I think it makes sense to drop the references about "downgrading" 
> > mm->mmap_sem in the documentation since populate_vma_page_range() can be 
> > called with it held either for read or write depending on the context.
> 
> I'm not sure what references you're talking about.
> 
> Is it about this part:
> 
>  * If @nonblocking is non-NULL, it must held for read only and may be
>  * released.  If it's released, *@nonblocking will be set to 0.
> 
> ?
> 

No, I was agreeing with your removal from the documentation:

@@ -463,21 +463,11 @@ populate the page table.
 
 To mlock a range of memory under the unevictable/mlock infrastructure, the
 mmap() handler and task address space expansion functions call
-mlock_vma_pages_range() specifying the vma and the address range to mlock.
-mlock_vma_pages_range() filters VMAs like mlock_fixup(), as described above in
-"Filtering Special VMAs".  It will clear the VM_LOCKED flag, which will have
-already been set by the caller, in filtered VMAs.  Thus these VMA's need not be
-visited for munlock when the region is unmapped.
-
-For "normal" VMAs, mlock_vma_pages_range() calls __mlock_vma_pages_range() to
-fault/allocate the pages and mlock them.  Again, like mlock_fixup(),
-mlock_vma_pages_range() downgrades the mmap semaphore to read mode before
-attempting to fault/allocate and mlock the pages and "upgrades" the semaphore
-back to write mode before returning.
-
-The callers of mlock_vma_pages_range() will have already added the memory range
+populate_vma_page_range() specifying the vma and the address range to mlock.
+
+The callers of populate_vma_page_range() will have already added the memory range
 to be mlocked to the task's "locked_vm".  To account for filtered VMAs,
-mlock_vma_pages_range() returns the number of pages NOT mlocked.  All of the
+populate_vma_page_range() returns the number of pages NOT mlocked.  All of the
 callers then subtract a non-negative return value from the task's locked_vm.  A
 negative return value represent an error - for example, from get_user_pages()
 attempting to fault in a VMA with PROT_NONE access.  In this case, we leave the

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[PATCH 3/4] mm: move gup() -> posix mlock() error conversion out of __mm_populate

[Kirill A. Shutemov]

This is praparation to moving mm_populate()-related code out of
mm/mlock.c.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
---
 mm/mlock.c | 11 +++++++----
 1 file changed, 7 insertions(+), 4 deletions(-)

diff --git a/mm/mlock.c b/mm/mlock.c
index c3ea18323034..0837fdb26047 100644
--- a/mm/mlock.c
+++ b/mm/mlock.c
@@ -712,7 +712,6 @@ int __mm_populate(unsigned long start, unsigned long len, int ignore_errors)
 				ret = 0;
 				continue;	/* continue at next VMA */
 			}
-			ret = __mlock_posix_error_return(ret);
 			break;
 		}
 		nend = nstart + ret * PAGE_SIZE;
@@ -750,9 +749,13 @@ SYSCALL_DEFINE2(mlock, unsigned long, start, size_t, len)
 		error = do_mlock(start, len, 1);
 
 	up_write(&current->mm->mmap_sem);
-	if (!error)
-		error = __mm_populate(start, len, 0);
-	return error;
+	if (error)
+		return error;
+
+	error = __mm_populate(start, len, 0);
+	if (error)
+		return  __mlock_posix_error_return(error);
+	return 0;
 }
 
 SYSCALL_DEFINE2(munlock, unsigned long, start, size_t, len)
-- 
2.1.4

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Re: [PATCH 3/4] mm: move gup() -> posix mlock() error conversion out of __mm_populate

[David Rientjes]

On Wed, 11 Feb 2015, Kirill A. Shutemov wrote:

> This is praparation to moving mm_populate()-related code out of
> mm/mlock.c.
> 

s/praparation/preparation/

> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> ---
>  mm/mlock.c | 11 +++++++----
>  1 file changed, 7 insertions(+), 4 deletions(-)
> 
> diff --git a/mm/mlock.c b/mm/mlock.c
> index c3ea18323034..0837fdb26047 100644
> --- a/mm/mlock.c
> +++ b/mm/mlock.c
> @@ -712,7 +712,6 @@ int __mm_populate(unsigned long start, unsigned long len, int ignore_errors)
>  				ret = 0;
>  				continue;	/* continue at next VMA */
>  			}
> -			ret = __mlock_posix_error_return(ret);
>  			break;
>  		}
>  		nend = nstart + ret * PAGE_SIZE;
> @@ -750,9 +749,13 @@ SYSCALL_DEFINE2(mlock, unsigned long, start, size_t, len)
>  		error = do_mlock(start, len, 1);
>  
>  	up_write(&current->mm->mmap_sem);
> -	if (!error)
> -		error = __mm_populate(start, len, 0);
> -	return error;
> +	if (error)
> +		return error;
> +
> +	error = __mm_populate(start, len, 0);
> +	if (error)
> +		return  __mlock_posix_error_return(error);

Extra space?

> +	return 0;
>  }
>  
>  SYSCALL_DEFINE2(munlock, unsigned long, start, size_t, len)

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[PATCH 4/4] mm: move mm_populate()-related code to mm/gup.c

[Kirill A. Shutemov]

It's odd that we have populate_vma_page_range() and __mm_populate() in
mm/mlock.c. It's implementation of generic memory population and
mlocking is one of possible side effect, if VM_LOCKED is set.

__get_user_pages() is core of the implementation. Let's move the code
mm/gup.c.

Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
---
 mm/gup.c   | 118 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 mm/mlock.c | 118 -------------------------------------------------------------
 2 files changed, 118 insertions(+), 118 deletions(-)

diff --git a/mm/gup.c b/mm/gup.c
index 1b114ba9aebf..ca7b607ab671 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -819,6 +819,124 @@ long get_user_pages(struct task_struct *tsk, struct mm_struct *mm,
 EXPORT_SYMBOL(get_user_pages);
 
 /**
+ * populate_vma_page_range() -  populate a range of pages in the vma.
+ * @vma:   target vma
+ * @start: start address
+ * @end:   end address
+ * @nonblocking:
+ *
+ * This takes care of mlocking the pages too if VM_LOCKED is set.
+ *
+ * return 0 on success, negative error code on error.
+ *
+ * vma->vm_mm->mmap_sem must be held.
+ *
+ * If @nonblocking is NULL, it may be held for read or write and will
+ * be unperturbed.
+ *
+ * If @nonblocking is non-NULL, it must held for read only and may be
+ * released.  If it's released, *@nonblocking will be set to 0.
+ */
+long populate_vma_page_range(struct vm_area_struct *vma,
+		unsigned long start, unsigned long end, int *nonblocking)
+{
+	struct mm_struct *mm = vma->vm_mm;
+	unsigned long nr_pages = (end - start) / PAGE_SIZE;
+	int gup_flags;
+
+	VM_BUG_ON(start & ~PAGE_MASK);
+	VM_BUG_ON(end   & ~PAGE_MASK);
+	VM_BUG_ON_VMA(start < vma->vm_start, vma);
+	VM_BUG_ON_VMA(end   > vma->vm_end, vma);
+	VM_BUG_ON_MM(!rwsem_is_locked(&mm->mmap_sem), mm);
+
+	gup_flags = FOLL_TOUCH | FOLL_POPULATE;
+	/*
+	 * We want to touch writable mappings with a write fault in order
+	 * to break COW, except for shared mappings because these don't COW
+	 * and we would not want to dirty them for nothing.
+	 */
+	if ((vma->vm_flags & (VM_WRITE | VM_SHARED)) == VM_WRITE)
+		gup_flags |= FOLL_WRITE;
+
+	/*
+	 * We want mlock to succeed for regions that have any permissions
+	 * other than PROT_NONE.
+	 */
+	if (vma->vm_flags & (VM_READ | VM_WRITE | VM_EXEC))
+		gup_flags |= FOLL_FORCE;
+
+	/*
+	 * We made sure addr is within a VMA, so the following will
+	 * not result in a stack expansion that recurses back here.
+	 */
+	return __get_user_pages(current, mm, start, nr_pages, gup_flags,
+				NULL, NULL, nonblocking);
+}
+
+/*
+ * __mm_populate - populate and/or mlock pages within a range of address space.
+ *
+ * This is used to implement mlock() and the MAP_POPULATE / MAP_LOCKED mmap
+ * flags. VMAs must be already marked with the desired vm_flags, and
+ * mmap_sem must not be held.
+ */
+int __mm_populate(unsigned long start, unsigned long len, int ignore_errors)
+{
+	struct mm_struct *mm = current->mm;
+	unsigned long end, nstart, nend;
+	struct vm_area_struct *vma = NULL;
+	int locked = 0;
+	long ret = 0;
+
+	VM_BUG_ON(start & ~PAGE_MASK);
+	VM_BUG_ON(len != PAGE_ALIGN(len));
+	end = start + len;
+
+	for (nstart = start; nstart < end; nstart = nend) {
+		/*
+		 * We want to fault in pages for [nstart; end) address range.
+		 * Find first corresponding VMA.
+		 */
+		if (!locked) {
+			locked = 1;
+			down_read(&mm->mmap_sem);
+			vma = find_vma(mm, nstart);
+		} else if (nstart >= vma->vm_end)
+			vma = vma->vm_next;
+		if (!vma || vma->vm_start >= end)
+			break;
+		/*
+		 * Set [nstart; nend) to intersection of desired address
+		 * range with the first VMA. Also, skip undesirable VMA types.
+		 */
+		nend = min(end, vma->vm_end);
+		if (vma->vm_flags & (VM_IO | VM_PFNMAP))
+			continue;
+		if (nstart < vma->vm_start)
+			nstart = vma->vm_start;
+		/*
+		 * Now fault in a range of pages. populate_vma_page_range()
+		 * double checks the vma flags, so that it won't mlock pages
+		 * if the vma was already munlocked.
+		 */
+		ret = populate_vma_page_range(vma, nstart, nend, &locked);
+		if (ret < 0) {
+			if (ignore_errors) {
+				ret = 0;
+				continue;	/* continue at next VMA */
+			}
+			break;
+		}
+		nend = nstart + ret * PAGE_SIZE;
+		ret = 0;
+	}
+	if (locked)
+		up_read(&mm->mmap_sem);
+	return ret;	/* 0 or negative error code */
+}
+
+/**
  * get_dump_page() - pin user page in memory while writing it to core dump
  * @addr: user address
  *
diff --git a/mm/mlock.c b/mm/mlock.c
index 0837fdb26047..a80ee4286865 100644
--- a/mm/mlock.c
+++ b/mm/mlock.c
@@ -205,62 +205,6 @@ out:
 	return nr_pages - 1;
 }
 
-/**
- * populate_vma_page_range() -  populate a range of pages in the vma.
- * @vma:   target vma
- * @start: start address
- * @end:   end address
- * @nonblocking:
- *
- * This takes care of mlocking the pages too if VM_LOCKED is set.
- *
- * return 0 on success, negative error code on error.
- *
- * vma->vm_mm->mmap_sem must be held.
- *
- * If @nonblocking is NULL, it may be held for read or write and will
- * be unperturbed.
- *
- * If @nonblocking is non-NULL, it must held for read only and may be
- * released.  If it's released, *@nonblocking will be set to 0.
- */
-long populate_vma_page_range(struct vm_area_struct *vma,
-		unsigned long start, unsigned long end, int *nonblocking)
-{
-	struct mm_struct *mm = vma->vm_mm;
-	unsigned long nr_pages = (end - start) / PAGE_SIZE;
-	int gup_flags;
-
-	VM_BUG_ON(start & ~PAGE_MASK);
-	VM_BUG_ON(end   & ~PAGE_MASK);
-	VM_BUG_ON_VMA(start < vma->vm_start, vma);
-	VM_BUG_ON_VMA(end   > vma->vm_end, vma);
-	VM_BUG_ON_MM(!rwsem_is_locked(&mm->mmap_sem), mm);
-
-	gup_flags = FOLL_TOUCH | FOLL_POPULATE;
-	/*
-	 * We want to touch writable mappings with a write fault in order
-	 * to break COW, except for shared mappings because these don't COW
-	 * and we would not want to dirty them for nothing.
-	 */
-	if ((vma->vm_flags & (VM_WRITE | VM_SHARED)) == VM_WRITE)
-		gup_flags |= FOLL_WRITE;
-
-	/*
-	 * We want mlock to succeed for regions that have any permissions
-	 * other than PROT_NONE.
-	 */
-	if (vma->vm_flags & (VM_READ | VM_WRITE | VM_EXEC))
-		gup_flags |= FOLL_FORCE;
-
-	/*
-	 * We made sure addr is within a VMA, so the following will
-	 * not result in a stack expansion that recurses back here.
-	 */
-	return __get_user_pages(current, mm, start, nr_pages, gup_flags,
-				NULL, NULL, nonblocking);
-}
-
 /*
  * convert get_user_pages() return value to posix mlock() error
  */
@@ -660,68 +604,6 @@ static int do_mlock(unsigned long start, size_t len, int on)
 	return error;
 }
 
-/*
- * __mm_populate - populate and/or mlock pages within a range of address space.
- *
- * This is used to implement mlock() and the MAP_POPULATE / MAP_LOCKED mmap
- * flags. VMAs must be already marked with the desired vm_flags, and
- * mmap_sem must not be held.
- */
-int __mm_populate(unsigned long start, unsigned long len, int ignore_errors)
-{
-	struct mm_struct *mm = current->mm;
-	unsigned long end, nstart, nend;
-	struct vm_area_struct *vma = NULL;
-	int locked = 0;
-	long ret = 0;
-
-	VM_BUG_ON(start & ~PAGE_MASK);
-	VM_BUG_ON(len != PAGE_ALIGN(len));
-	end = start + len;
-
-	for (nstart = start; nstart < end; nstart = nend) {
-		/*
-		 * We want to fault in pages for [nstart; end) address range.
-		 * Find first corresponding VMA.
-		 */
-		if (!locked) {
-			locked = 1;
-			down_read(&mm->mmap_sem);
-			vma = find_vma(mm, nstart);
-		} else if (nstart >= vma->vm_end)
-			vma = vma->vm_next;
-		if (!vma || vma->vm_start >= end)
-			break;
-		/*
-		 * Set [nstart; nend) to intersection of desired address
-		 * range with the first VMA. Also, skip undesirable VMA types.
-		 */
-		nend = min(end, vma->vm_end);
-		if (vma->vm_flags & (VM_IO | VM_PFNMAP))
-			continue;
-		if (nstart < vma->vm_start)
-			nstart = vma->vm_start;
-		/*
-		 * Now fault in a range of pages. populate_vma_page_range()
-		 * double checks the vma flags, so that it won't mlock pages
-		 * if the vma was already munlocked.
-		 */
-		ret = populate_vma_page_range(vma, nstart, nend, &locked);
-		if (ret < 0) {
-			if (ignore_errors) {
-				ret = 0;
-				continue;	/* continue at next VMA */
-			}
-			break;
-		}
-		nend = nstart + ret * PAGE_SIZE;
-		ret = 0;
-	}
-	if (locked)
-		up_read(&mm->mmap_sem);
-	return ret;	/* 0 or negative error code */
-}
-
 SYSCALL_DEFINE2(mlock, unsigned long, start, size_t, len)
 {
 	unsigned long locked;
-- 
2.1.4

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Re: [PATCH 4/4] mm: move mm_populate()-related code to mm/gup.c

[David Rientjes]

On Wed, 11 Feb 2015, Kirill A. Shutemov wrote:

> It's odd that we have populate_vma_page_range() and __mm_populate() in
> mm/mlock.c. It's implementation of generic memory population and
> mlocking is one of possible side effect, if VM_LOCKED is set.
> 
> __get_user_pages() is core of the implementation. Let's move the code
> mm/gup.c.
> 
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>

Acked-by: David Rientjes <rientjes@google.com>

Nice cleanup!

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Re: [PATCH 0/4] Cleanup mm_populate() codepath

[Linus Torvalds]

On Wed, Feb 11, 2015 at 9:12 AM, Kirill A. Shutemov
<kirill.shutemov@linux.intel.com> wrote:
> While reading mlock()- and mm_populate()-related code, I've found several
> things confusing. This patchset cleanup the codepath for future readers.

Looks sane to me. Ack.

                 Linus

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