Add __GFP_MOVABLE for callers to flag allocations from high memory that may be migrated

It is often known at allocation time whether a page may be migrated or not.
This patch adds a flag called __GFP_MOVABLE and a new mask called
GFP_HIGH_MOVABLE.  Allocations using the __GFP_MOVABLE can be either migrated
using the page migration mechanism or reclaimed by syncing with backing
storage and discarding.

An API function very similar to alloc_zeroed_user_highpage() is added for
__GFP_MOVABLE allocations called alloc_zeroed_user_highpage_movable().  The
flags used by alloc_zeroed_user_highpage() are not changed because it would
change the semantics of an existing API.  After this patch is applied there
are no in-kernel users of alloc_zeroed_user_highpage() so it probably should
be marked deprecated if this patch is merged.

Note that this patch includes a minor cleanup to the use of __GFP_ZERO in
shmem.c to keep all flag modifications to inode->mapping in the
shmem_dir_alloc() helper function.  This clean-up suggestion is courtesy of
Hugh Dickens.

Additional credit goes to Christoph Lameter and Linus Torvalds for shaping the
concept.  Credit to Hugh Dickens for catching issues with shmem swap vector
and ramfs allocations.

[akpm@linux-foundation.org: build fix]
[hugh@veritas.com: __GFP_ZERO cleanup]
Signed-off-by: Mel Gorman <mel@csn.ul.ie>
Cc: Andy Whitcroft <apw@shadowen.org>
Cc: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 64 insertions, 3 deletions

diff --git a/include/linux/gfp.h b/include/linux/gfp.h
index 0d2ef0b082a6..e5882fe49f83 100644
--- a/include/linux/gfp.h
+++ b/include/linux/gfp.h
@@ -30,6 +30,9 @@ struct vm_area_struct;
  * cannot handle allocation failures.
  *
  * __GFP_NORETRY: The VM implementation must not retry indefinitely.
+ *
+ * __GFP_MOVABLE: Flag that this page will be movable by the page migration
+ * mechanism or reclaimed
  */
 #define __GFP_WAIT      ((__force gfp_t)0x10u)  /* Can wait and reschedule? */
 #define __GFP_HIGH      ((__force gfp_t)0x20u)  /* Should access emergency pools? */
@@ -45,6 +48,7 @@ struct vm_area_struct;
 #define __GFP_NOMEMALLOC ((__force gfp_t)0x10000u) /* Don't use emergency reserves */
 #define __GFP_HARDWALL   ((__force gfp_t)0x20000u) /* Enforce hardwall cpuset memory allocs */
 #define __GFP_THISNODE  ((__force gfp_t)0x40000u)/* No fallback, no policies */
+#define __GFP_MOVABLE   ((__force gfp_t)0x80000u) /* Page is movable */
 
 #define __GFP_BITS_SHIFT 20     /* Room for 20 __GFP_FOO bits */
 #define __GFP_BITS_MASK ((__force gfp_t)((1 << __GFP_BITS_SHIFT) - 1))
@@ -53,7 +57,8 @@ struct vm_area_struct;
 #define GFP_LEVEL_MASK (__GFP_WAIT|__GFP_HIGH|__GFP_IO|__GFP_FS| \
                         __GFP_COLD|__GFP_NOWARN|__GFP_REPEAT| \
                         __GFP_NOFAIL|__GFP_NORETRY|__GFP_COMP| \
-                        __GFP_NOMEMALLOC|__GFP_HARDWALL|__GFP_THISNODE)
+                        __GFP_NOMEMALLOC|__GFP_HARDWALL|__GFP_THISNODE| \
+                        __GFP_MOVABLE)
 
 /* This equals 0, but use constants in case they ever change */
 #define GFP_NOWAIT      (GFP_ATOMIC & ~__GFP_HIGH)
@@ -65,6 +70,15 @@ struct vm_area_struct;
 #define GFP_USER        (__GFP_WAIT | __GFP_IO | __GFP_FS | __GFP_HARDWALL)
 #define GFP_HIGHUSER    (__GFP_WAIT | __GFP_IO | __GFP_FS | __GFP_HARDWALL | \
                          __GFP_HIGHMEM)
+#define GFP_HIGHUSER_MOVABLE    (__GFP_WAIT | __GFP_IO | __GFP_FS | \
+                                 __GFP_HARDWALL | __GFP_HIGHMEM | \
+                                 __GFP_MOVABLE)
+#define GFP_NOFS_PAGECACHE      (__GFP_WAIT | __GFP_IO | __GFP_MOVABLE)
+#define GFP_USER_PAGECACHE      (__GFP_WAIT | __GFP_IO | __GFP_FS | \
+                                 __GFP_HARDWALL | __GFP_MOVABLE)
+#define GFP_HIGHUSER_PAGECACHE  (__GFP_WAIT | __GFP_IO | __GFP_FS | \
+                                 __GFP_HARDWALL | __GFP_HIGHMEM | \
+                                 __GFP_MOVABLE)
 
 #ifdef CONFIG_NUMA
 #define GFP_THISNODE    (__GFP_THISNODE | __GFP_NOWARN | __GFP_NORETRY)
diff --git a/include/linux/highmem.h b/include/linux/highmem.h
index 98e2cce996a4..12c5e4e3135a 100644
--- a/include/linux/highmem.h
+++ b/include/linux/highmem.h
@@ -73,10 +73,27 @@ static inline void clear_user_highpage(struct page *page, unsigned long vaddr)
 }
 
 #ifndef __HAVE_ARCH_ALLOC_ZEROED_USER_HIGHPAGE
+/**
+ * __alloc_zeroed_user_highpage - Allocate a zeroed HIGHMEM page for a VMA with caller-specified movable GFP flags
+ * @movableflags: The GFP flags related to the pages future ability to move like __GFP_MOVABLE
+ * @vma: The VMA the page is to be allocated for
+ * @vaddr: The virtual address the page will be inserted into
+ *
+ * This function will allocate a page for a VMA but the caller is expected
+ * to specify via movableflags whether the page will be movable in the
+ * future or not
+ *
+ * An architecture may override this function by defining
+ * __HAVE_ARCH_ALLOC_ZEROED_USER_HIGHPAGE and providing their own
+ * implementation.
+ */
 static inline struct page *
-alloc_zeroed_user_highpage(struct vm_area_struct *vma, unsigned long vaddr)
+__alloc_zeroed_user_highpage(gfp_t movableflags,
+                        struct vm_area_struct *vma,
+                        unsigned long vaddr)
 {
-        struct page *page = alloc_page_vma(GFP_HIGHUSER, vma, vaddr);
+        struct page *page = alloc_page_vma(GFP_HIGHUSER | movableflags,
+                        vma, vaddr);
 
         if (page)
                 clear_user_highpage(page, vaddr);
@@ -85,6 +102,36 @@ alloc_zeroed_user_highpage(struct vm_area_struct *vma, unsigned long vaddr)
 }
 #endif
 
+/**
+ * alloc_zeroed_user_highpage - Allocate a zeroed HIGHMEM page for a VMA
+ * @vma: The VMA the page is to be allocated for
+ * @vaddr: The virtual address the page will be inserted into
+ *
+ * This function will allocate a page for a VMA that the caller knows will
+ * not be able to move in the future using move_pages() or reclaim. If it
+ * is known that the page can move, use alloc_zeroed_user_highpage_movable
+ */
+static inline struct page *
+alloc_zeroed_user_highpage(struct vm_area_struct *vma, unsigned long vaddr)
+{
+        return __alloc_zeroed_user_highpage(0, vma, vaddr);
+}
+
+/**
+ * alloc_zeroed_user_highpage_movable - Allocate a zeroed HIGHMEM page for a VMA that the caller knows can move
+ * @vma: The VMA the page is to be allocated for
+ * @vaddr: The virtual address the page will be inserted into
+ *
+ * This function will allocate a page for a VMA that the caller knows will
+ * be able to migrate in the future using move_pages() or reclaimed
+ */
+static inline struct page *
+alloc_zeroed_user_highpage_movable(struct vm_area_struct *vma,
+                                        unsigned long vaddr)
+{
+        return __alloc_zeroed_user_highpage(__GFP_MOVABLE, vma, vaddr);
+}
+
 static inline void clear_highpage(struct page *page)
 {
         void *kaddr = kmap_atomic(page, KM_USER0);