mm: rework do_pages_move() to work on page_sized chunks

Rework do_pages_move() to work by page-sized chunks of struct page_to_node
that are passed to do_move_page_to_node_array().  We now only have to
allocate a single page instead a possibly very large vmalloc area to store
all page_to_node entries.

As a result, new_page_node() will now have a very small lookup, hidding
much of the overall sys_move_pages() overhead.

Signed-off-by: Brice Goglin <Brice.Goglin@inria.fr>
Signed-off-by: Nathalie Furmento <Nathalie.Furmento@labri.fr>
Acked-by: Christoph Lameter <cl@linux-foundation.org>
Cc: Nick Piggin <nickpiggin@yahoo.com.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 44 insertions, 35 deletions

diff --git a/mm/migrate.c b/mm/migrate.c
index 21631ab8c08b..0a75716cb736 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -919,41 +919,43 @@ static int do_pages_move(struct mm_struct *mm, struct task_struct *task,
                          const int __user *nodes,
                          int __user *status, int flags)
 {
-        struct page_to_node *pm = NULL;
+        struct page_to_node *pm;
         nodemask_t task_nodes;
-        int err = 0;
-        int i;
+        unsigned long chunk_nr_pages;
+        unsigned long chunk_start;
+        int err;
 
         task_nodes = cpuset_mems_allowed(task);
 
-        /* Limit nr_pages so that the multiplication may not overflow */
-        if (nr_pages >= ULONG_MAX / sizeof(struct page_to_node) - 1) {
-                err = -E2BIG;
-                goto out;
-        }
-
-        pm = vmalloc((nr_pages + 1) * sizeof(struct page_to_node));
-        if (!pm) {
-                err = -ENOMEM;
+        err = -ENOMEM;
+        pm = (struct page_to_node *)__get_free_page(GFP_KERNEL);
+        if (!pm)
                 goto out;
-        }
-
         /*
-         * Get parameters from user space and initialize the pm
-         * array. Return various errors if the user did something wrong.
+         * Store a chunk of page_to_node array in a page,
+         * but keep the last one as a marker
          */
-        for (i = 0; i < nr_pages; i++) {
-                const void __user *p;
+        chunk_nr_pages = (PAGE_SIZE / sizeof(struct page_to_node)) - 1;
 
-                err = -EFAULT;
-                if (get_user(p, pages + i))
-                        goto out_pm;
+        for (chunk_start = 0;
+             chunk_start < nr_pages;
+             chunk_start += chunk_nr_pages) {
+                int j;
 
-                pm[i].addr = (unsigned long)p;
-                if (nodes) {
+                if (chunk_start + chunk_nr_pages > nr_pages)
+                        chunk_nr_pages = nr_pages - chunk_start;
+
+                /* fill the chunk pm with addrs and nodes from user-space */
+                for (j = 0; j < chunk_nr_pages; j++) {
+                        const void __user *p;
                         int node;
 
-                        if (get_user(node, nodes + i))
+                        err = -EFAULT;
+                        if (get_user(p, pages + j + chunk_start))
+                                goto out_pm;
+                        pm[j].addr = (unsigned long) p;
+
+                        if (get_user(node, nodes + j + chunk_start))
                                 goto out_pm;
 
                         err = -ENODEV;
@@ -964,22 +966,29 @@ static int do_pages_move(struct mm_struct *mm, struct task_struct *task,
                         if (!node_isset(node, task_nodes))
                                 goto out_pm;
 
-                        pm[i].node = node;
-                } else
-                        pm[i].node = 0; /* anything to not match MAX_NUMNODES */
-        }
-        /* End marker */
-        pm[nr_pages].node = MAX_NUMNODES;
+                        pm[j].node = node;
+                }
+
+                /* End marker for this chunk */
+                pm[chunk_nr_pages].node = MAX_NUMNODES;
+
+                /* Migrate this chunk */
+                err = do_move_page_to_node_array(mm, pm,
+                                                 flags & MPOL_MF_MOVE_ALL);
+                if (err < 0)
+                        goto out_pm;
 
-        err = do_move_page_to_node_array(mm, pm, flags & MPOL_MF_MOVE_ALL);
-        if (err >= 0)
                 /* Return status information */
-                for (i = 0; i < nr_pages; i++)
-                        if (put_user(pm[i].status, status + i))
+                for (j = 0; j < chunk_nr_pages; j++)
+                        if (put_user(pm[j].status, status + j + chunk_start)) {
                                 err = -EFAULT;
+                                goto out_pm;
+                        }
+        }
+        err = 0;
 
 out_pm:
-        vfree(pm);
+        free_page((unsigned long)pm);
 out:
         return err;
 }