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Subject[PATCH 6/7] Direct Migration V5: upgrade MPOL_MF_MOVE and sys_migrate_pages()
Modify policy layer to support direct page migration

- Add migrate_pages_to() allowing the migration of a list of pages to a
a specified node or to vma with a specific allocation policy in sets
of MIGRATE_CHUNK_SIZE pages

- Modify do_migrate_pages() to do a staged move of pages from the
source nodes to the target nodes.

V3->V4: Fixed up to be based on the swap migration code in 2.6.15-rc1-mm2.

V1->V2:
- Migrate processes in chunks of MIGRATE_CHUNK_SIZE

Signed-off-by: Paul Jackson <pj@sgi.com>
Signed-off-by: Christoph Lameter <clameter@sgi.com>

Index: linux-2.6.15-rc2-mm1/mm/mempolicy.c
===================================================================
--- linux-2.6.15-rc2-mm1.orig/mm/mempolicy.c 2005-11-28 12:30:08.000000000 -0800
+++ linux-2.6.15-rc2-mm1/mm/mempolicy.c 2005-11-28 12:36:57.000000000 -0800
@@ -95,6 +95,9 @@
#define MPOL_MF_INVERT (MPOL_MF_INTERNAL << 1) /* Invert check for nodemask */
#define MPOL_MF_STATS (MPOL_MF_INTERNAL << 2) /* Gather statistics */

+/* The number of pages to migrate per call to migrate_pages() */
+#define MIGRATE_CHUNK_SIZE 256
+
static kmem_cache_t *policy_cache;
static kmem_cache_t *sn_cache;

@@ -573,24 +576,96 @@ static void migrate_page_add(struct vm_a
}
}

-static int swap_pages(struct list_head *pagelist)
+/*
+ * Migrate the list 'pagelist' of pages to a certain destination.
+ *
+ * Specify destination with either non-NULL vma or dest_node >= 0
+ * Return the number of pages not migrated or error code
+ */
+static int migrate_pages_to(struct list_head *pagelist,
+ struct vm_area_struct *vma, int dest)
{
+ LIST_HEAD(newlist);
LIST_HEAD(moved);
LIST_HEAD(failed);
- int n;
+ int err = 0;
+ int nr_pages;
+ struct page *page;
+ struct list_head *p;

- n = migrate_pages(pagelist, NULL, &moved, &failed);
- putback_lru_pages(&failed);
- putback_lru_pages(&moved);
+redo:
+ nr_pages = 0;
+ list_for_each(p, pagelist) {
+ if (vma)
+ page = alloc_page_vma(GFP_HIGHUSER, vma,
+ vma->vm_start);
+ else
+ page = alloc_pages_node(dest, GFP_HIGHUSER, 0);

- return n;
+ if (!page) {
+ err = -ENOMEM;
+ goto out;
+ }
+ list_add(&page->lru, &newlist);
+ nr_pages++;
+ if (nr_pages > MIGRATE_CHUNK_SIZE);
+ break;
+ }
+ err = migrate_pages(pagelist, &newlist, &moved, &failed);
+
+ putback_lru_pages(&moved); /* Call release pages instead ?? */
+
+ if (err >= 0 && list_empty(&newlist) && !list_empty(pagelist))
+ goto redo;
+out:
+ /* Return leftover allocated pages */
+ while (!list_empty(&newlist)) {
+ page = list_entry(newlist.next, struct page, lru);
+ list_del(&page->lru);
+ __free_page(page);
+ }
+ list_splice(&failed, pagelist);
+ if (err < 0)
+ return err;
+
+ /* Calculate number of leftover pages */
+ nr_pages = 0;
+ list_for_each(p, pagelist)
+ nr_pages++;
+ return nr_pages;
+}
+
+/*
+ * Migrate pages from one node to a target node.
+ * Returns error or the number of pages not migrated.
+ */
+int migrate_to_node(struct mm_struct *mm, int source, int dest, int flags)
+{
+ nodemask_t nmask;
+ LIST_HEAD(pagelist);
+ int err = 0;
+
+ nodes_clear(nmask);
+ node_set(source, nmask);
+
+ check_range(mm, mm->mmap->vm_start, TASK_SIZE, &nmask,
+ flags | MPOL_MF_DISCONTIG_OK,
+ &pagelist);
+
+ if (!list_empty(&pagelist)) {
+
+ err = migrate_pages_to(&pagelist, NULL, dest);
+
+ if (!list_empty(&pagelist))
+ putback_lru_pages(&pagelist);
+
+ }
+ return err;
}

/*
- * For now migrate_pages simply swaps out the pages from nodes that are in
- * the source set but not in the target set. In the future, we would
- * want a function that moves pages between the two nodesets in such
- * a way as to preserve the physical layout as much as possible.
+ * Move pages between the two nodesets so as to preserve the physical
+ * layout as much as possible.
*
* Returns the number of page that could not be moved.
*/
@@ -598,22 +673,76 @@ int do_migrate_pages(struct mm_struct *m
const nodemask_t *from_nodes, const nodemask_t *to_nodes, int flags)
{
LIST_HEAD(pagelist);
- int count = 0;
- nodemask_t nodes;
+ int busy = 0;
+ int err = 0;
+ nodemask_t tmp;

- nodes_andnot(nodes, *from_nodes, *to_nodes);
+ down_read(&mm->mmap_sem);

- down_read(&mm->mmap_sem);
- check_range(mm, mm->mmap->vm_start, TASK_SIZE, &nodes,
- flags | MPOL_MF_DISCONTIG_OK, &pagelist);
+/* Find a 'source' bit set in 'tmp' whose corresponding 'dest'
+ * bit in 'to' is not also set in 'tmp'. Clear the found 'source'
+ * bit in 'tmp', and return that <source, dest> pair for migration.
+ * The pair of nodemasks 'to' and 'from' define the map.
+ *
+ * If no pair of bits is found that way, fallback to picking some
+ * pair of 'source' and 'dest' bits that are not the same. If the
+ * 'source' and 'dest' bits are the same, this represents a node
+ * that will be migrating to itself, so no pages need move.
+ *
+ * If no bits are left in 'tmp', or if all remaining bits left
+ * in 'tmp' correspond to the same bit in 'to', return false
+ * (nothing left to migrate).
+ *
+ * This lets us pick a pair of nodes to migrate between, such that
+ * if possible the dest node is not already occupied by some other
+ * source node, minimizing the risk of overloading the memory on a
+ * node that would happen if we migrated incoming memory to a node
+ * before migrating outgoing memory source that same node.
+ *
+ * A single scan of tmp is sufficient. As we go, we remember the
+ * most recent <s, d> pair that moved (s != d). If we find a pair
+ * that not only moved, but what's better, moved to an empty slot
+ * (d is not set in tmp), then we break out then, with that pair.
+ * Otherwise when we finish scannng from_tmp, we at least have the
+ * most recent <s, d> pair that moved. If we get all the way through
+ * the scan of tmp without finding any node that moved, much less
+ * moved to an empty node, then there is nothing left worth migrating.
+ */

- if (!list_empty(&pagelist)) {
- count = swap_pages(&pagelist);
- putback_lru_pages(&pagelist);
+ tmp = *from_nodes;
+ while (!nodes_empty(tmp)) {
+ int s,d;
+ int source = -1;
+ int dest = 0;
+
+ for_each_node_mask(s, tmp) {
+
+ d = node_remap(s, *from_nodes, *to_nodes);
+ if (s == d)
+ continue;
+
+ source = s; /* Node moved. Memorize */
+ dest = d;
+
+ /* dest not in remaining from nodes? */
+ if (!node_isset(dest, tmp))
+ break;
+ }
+ if (source == -1)
+ break;
+
+ node_clear(source, tmp);
+ err = migrate_to_node(mm, source, dest, flags);
+ if (err > 0)
+ busy += err;
+ if (err < 0)
+ break;
}

up_read(&mm->mmap_sem);
- return count;
+ if (err < 0)
+ return err;
+ return busy;
}

long do_mbind(unsigned long start, unsigned long len,
@@ -673,8 +802,9 @@ long do_mbind(unsigned long start, unsig
int nr_failed = 0;

err = mbind_range(vma, start, end, new);
+
if (!list_empty(&pagelist))
- nr_failed = swap_pages(&pagelist);
+ nr_failed = migrate_pages_to(&pagelist, vma, -1);

if (!err && nr_failed && (flags & MPOL_MF_STRICT))
err = -EIO;
-
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