[Xen-devel] [PATCH v3 3/9] mm: Scrub pages in alloc_heap_pages() if needed

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

When allocating pages in alloc_heap_pages() first look for clean pages. If none
is found then retry, take pages marked as unscrubbed and scrub them.

Note that we shouldn't find unscrubbed pages in alloc_heap_pages() yet. However,
this will become possible when we stop scrubbing from free_heap_pages() and
instead do it from idle loop.

Signed-off-by: Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>
---
 xen/common/page_alloc.c |   96 ++++++++++++++++++++++++++++++++++------------
 1 files changed, 71 insertions(+), 25 deletions(-)

diff --git a/xen/common/page_alloc.c b/xen/common/page_alloc.c
index 9dcf6ee..055654d 100644
--- a/xen/common/page_alloc.c
+++ b/xen/common/page_alloc.c
@@ -700,34 +700,17 @@ static struct page_info *alloc_heap_pages(
     unsigned int order, unsigned int memflags,
     struct domain *d)
 {
-    unsigned int i, j, zone = 0, nodemask_retry = 0;
-    nodeid_t first_node, node = MEMF_get_node(memflags), req_node = node;
+    unsigned int i, j, zone, nodemask_retry;
+    nodeid_t first_node, node, req_node;
     unsigned long request = 1UL << order;
     struct page_info *pg;
-    nodemask_t nodemask = (d != NULL ) ? d->node_affinity : node_online_map;
-    bool_t need_tlbflush = 0;
+    nodemask_t nodemask;
+    bool need_scrub, need_tlbflush = false, use_unscrubbed = false;
     uint32_t tlbflush_timestamp = 0;
 
     /* Make sure there are enough bits in memflags for nodeID. */
     BUILD_BUG_ON((_MEMF_bits - _MEMF_node) < (8 * sizeof(nodeid_t)));
 
-    if ( node == NUMA_NO_NODE )
-    {
-        if ( d != NULL )
-        {
-            node = next_node(d->last_alloc_node, nodemask);
-            if ( node >= MAX_NUMNODES )
-                node = first_node(nodemask);
-        }
-        if ( node >= MAX_NUMNODES )
-            node = cpu_to_node(smp_processor_id());
-    }
-    first_node = node;
-
-    ASSERT(node < MAX_NUMNODES);
-    ASSERT(zone_lo <= zone_hi);
-    ASSERT(zone_hi < NR_ZONES);
-
     if ( unlikely(order > MAX_ORDER) )
         return NULL;
 
@@ -741,7 +724,10 @@ static struct page_info *alloc_heap_pages(
           total_avail_pages + tmem_freeable_pages()) &&
           ((memflags & MEMF_no_refcount) ||
            !d || d->outstanding_pages < request) )
-        goto not_found;
+    {
+        spin_unlock(&heap_lock);
+        return NULL;
+    }
 
     /*
      * TMEM: When available memory is scarce due to tmem absorbing it, allow
@@ -754,6 +740,28 @@ static struct page_info *alloc_heap_pages(
          tmem_freeable_pages() )
         goto try_tmem;
 
+ again:
+
+    nodemask_retry = 0;
+    nodemask = (d != NULL ) ? d->node_affinity : node_online_map;
+    node = req_node = MEMF_get_node(memflags);
+    if ( node == NUMA_NO_NODE )
+    {
+        if ( d != NULL )
+        {
+            node = next_node(d->last_alloc_node, nodemask);
+            if ( node >= MAX_NUMNODES )
+                node = first_node(nodemask);
+        }
+        if ( node >= MAX_NUMNODES )
+            node = cpu_to_node(smp_processor_id());
+    }
+    first_node = node;
+
+    ASSERT(node < MAX_NUMNODES);
+    ASSERT(zone_lo <= zone_hi);
+    ASSERT(zone_hi < NR_ZONES);
+
     /*
      * Start with requested node, but exhaust all node memory in requested 
      * zone before failing, only calc new node value if we fail to find memory 
@@ -769,8 +777,16 @@ static struct page_info *alloc_heap_pages(
 
             /* Find smallest order which can satisfy the request. */
             for ( j = order; j <= MAX_ORDER; j++ )
+            {
                 if ( (pg = page_list_remove_head(&heap(node, zone, j))) )
-                    goto found;
+                {
+                    if ( (order == 0) || use_unscrubbed ||
+                         !pg->u.free.dirty_head )
+                        goto found;
+
+                    page_list_add_tail(pg, &heap(node, zone, j));
+                }
+            }
         } while ( zone-- > zone_lo ); /* careful: unsigned zone may wrap */
 
         if ( (memflags & MEMF_exact_node) && req_node != NUMA_NO_NODE )
@@ -809,16 +825,32 @@ static struct page_info *alloc_heap_pages(
     }
 
  not_found:
+    /*
+     * If we couldn't find clean page let's search again and this time
+     * take unscrubbed pages if available.
+     */
+    if ( !use_unscrubbed )
+    {
+        use_unscrubbed = true;
+        goto again;
+    }
+
     /* No suitable memory blocks. Fail the request. */
     spin_unlock(&heap_lock);
     return NULL;
 
  found: 
+    need_scrub = pg->u.free.dirty_head;
+
     /* We may have to halve the chunk a number of times. */
     while ( j != order )
     {
-        PFN_ORDER(pg) = --j;
-        page_list_add(pg, &heap(node, zone, j));
+        /*
+         * Some of the sub-chunks may be clean but we will mark them
+         * as dirty (if need_scrub is set) to avoid traversing the
+         * array here.
+         */
+        page_list_add_scrub(pg, node, zone, --j, need_scrub);
         pg += 1 << j;
     }
 
@@ -832,6 +864,20 @@ static struct page_info *alloc_heap_pages(
     if ( d != NULL )
         d->last_alloc_node = node;
 
+    if ( need_scrub )
+    {
+        for ( i = 0; i < (1 << order); i++ )
+        {
+            if ( test_bit(_PGC_need_scrub, &pg[i].count_info) )
+            {
+                scrub_one_page(&pg[i]);
+                pg[i].count_info &= ~PGC_need_scrub;
+                node_need_scrub[node]--;
+            }
+        }
+        pg->u.free.dirty_head = false;
+    }
+
     for ( i = 0; i < (1 << order); i++ )
     {
         /* Reference count must continuously be zero for free pages. */
-- 
1.7.1


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