[Xen-devel] [PATCH v3 1/9] mm: Separate free page chunk merging into its own routine

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

This is needed for subsequent changes to memory scrubbing.

Signed-off-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
---

Changes in v3:
* Simplify merge_and_free_buddy() (and drop can_merge())

 xen/common/page_alloc.c |   74 ++++++++++++++++++++++++++---------------------
 1 files changed, 41 insertions(+), 33 deletions(-)

diff --git a/xen/common/page_alloc.c b/xen/common/page_alloc.c
index 9e41fb4..6fe55ee 100644
--- a/xen/common/page_alloc.c
+++ b/xen/common/page_alloc.c
@@ -919,11 +919,50 @@ static int reserve_offlined_page(struct page_info *head)
     return count;
 }
 
+/* Returns new buddy head. */
+static struct page_info *
+merge_and_free_buddy(struct page_info *pg, unsigned int node,
+                     unsigned int zone, unsigned int order)
+{
+    ASSERT(spin_is_locked(&heap_lock));
+
+    /* Merge chunks as far as possible. */
+    while ( order < MAX_ORDER )
+    {
+        unsigned long mask = 1UL << order;
+        struct page_info *buddy;
+
+        if ( (page_to_mfn(pg) & mask) )
+            buddy = pg - mask; /* Merge with predecessor block. */
+        else
+            buddy = pg + mask; /* Merge with successor block. */
+
+        if ( !mfn_valid(_mfn(page_to_mfn(buddy))) ||
+             !page_state_is(buddy, free) ||
+             (PFN_ORDER(buddy) != order) ||
+             (phys_to_nid(page_to_maddr(buddy)) != node) )
+            break;
+
+        page_list_del(buddy, &heap(node, zone, order));
+
+        /* Adjust current buddy head if we merged backwards. */
+        if ( buddy < pg )
+            pg = buddy;
+
+        order++;
+    }
+
+    PFN_ORDER(pg) = order;
+    page_list_add_tail(pg, &heap(node, zone, order));
+
+    return pg;
+}
+
 /* Free 2^@order set of pages. */
 static void free_heap_pages(
     struct page_info *pg, unsigned int order)
 {
-    unsigned long mask, mfn = page_to_mfn(pg);
+    unsigned long mfn = page_to_mfn(pg);
     unsigned int i, node = phys_to_nid(page_to_maddr(pg)), tainted = 0;
     unsigned int zone = page_to_zone(pg);
 
@@ -970,38 +1009,7 @@ static void free_heap_pages(
         midsize_alloc_zone_pages = max(
             midsize_alloc_zone_pages, total_avail_pages / MIDSIZE_ALLOC_FRAC);
 
-    /* Merge chunks as far as possible. */
-    while ( order < MAX_ORDER )
-    {
-        mask = 1UL << order;
-
-        if ( (page_to_mfn(pg) & mask) )
-        {
-            /* Merge with predecessor block? */
-            if ( !mfn_valid(_mfn(page_to_mfn(pg-mask))) ||
-                 !page_state_is(pg-mask, free) ||
-                 (PFN_ORDER(pg-mask) != order) ||
-                 (phys_to_nid(page_to_maddr(pg-mask)) != node) )
-                break;
-            pg -= mask;
-            page_list_del(pg, &heap(node, zone, order));
-        }
-        else
-        {
-            /* Merge with successor block? */
-            if ( !mfn_valid(_mfn(page_to_mfn(pg+mask))) ||
-                 !page_state_is(pg+mask, free) ||
-                 (PFN_ORDER(pg+mask) != order) ||
-                 (phys_to_nid(page_to_maddr(pg+mask)) != node) )
-                break;
-            page_list_del(pg + mask, &heap(node, zone, order));
-        }
-
-        order++;
-    }
-
-    PFN_ORDER(pg) = order;
-    page_list_add_tail(pg, &heap(node, zone, order));
+    pg = merge_and_free_buddy(pg, node, zone, order);
 
     if ( tainted )
         reserve_offlined_page(pg);
-- 
1.7.1


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