[PATCH v3 1/8] libxenguest: short-circuit "all-dirty" handling

[Jan Beulich <jbeulich@xxxxxxxx>]

For one it is unnecessary to fill a perhaps large chunk of memory with
all ones. Add a new parameter to send_dirty_pages() for callers to
indicate so.

Then it is further unnecessary to allocate the dirty bitmap altogether
when all that's ever going to happen is a single all-dirty run.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
Reviewed-by: Juergen Gross <jgross@xxxxxxxx>
Acked-by: Ian Jackson <iwj@xxxxxxxxxxxxxx>
---
NOTE: Ian demands that this not be committed without also committing
"libxenguest: avoid allocating unused deferred-pages bitmap" (because
of the ugly -1L).

--- a/tools/libs/guest/xg_sr_save.c
+++ b/tools/libs/guest/xg_sr_save.c
@@ -364,7 +364,7 @@ static int suspend_domain(struct xc_sr_c
  * Bitmap is bounded by p2m_size.
  */
 static int send_dirty_pages(struct xc_sr_context *ctx,
-                            unsigned long entries)
+                            unsigned long entries, bool all_dirty)
 {
     xc_interface *xch = ctx->xch;
     xen_pfn_t p;
@@ -375,7 +375,7 @@ static int send_dirty_pages(struct xc_sr
 
     for ( p = 0, written = 0; p < ctx->save.p2m_size; ++p )
     {
-        if ( !test_bit(p, dirty_bitmap) )
+        if ( !all_dirty && !test_bit(p, dirty_bitmap) )
             continue;
 
         rc = add_to_batch(ctx, p);
@@ -407,12 +407,7 @@ static int send_dirty_pages(struct xc_sr
  */
 static int send_all_pages(struct xc_sr_context *ctx)
 {
-    DECLARE_HYPERCALL_BUFFER_SHADOW(unsigned long, dirty_bitmap,
-                                    &ctx->save.dirty_bitmap_hbuf);
-
-    bitmap_set(dirty_bitmap, ctx->save.p2m_size);
-
-    return send_dirty_pages(ctx, ctx->save.p2m_size);
+    return send_dirty_pages(ctx, ctx->save.p2m_size, true /* all_dirty */);
 }
 
 static int enable_logdirty(struct xc_sr_context *ctx)
@@ -502,9 +497,6 @@ static int send_memory_live(struct xc_sr
     int rc;
     int policy_decision;
 
-    DECLARE_HYPERCALL_BUFFER_SHADOW(unsigned long, dirty_bitmap,
-                                    &ctx->save.dirty_bitmap_hbuf);
-
     precopy_policy_t precopy_policy = ctx->save.callbacks->precopy_policy;
     void *data = ctx->save.callbacks->data;
 
@@ -522,8 +514,6 @@ static int send_memory_live(struct xc_sr
     if ( precopy_policy == NULL )
         precopy_policy = simple_precopy_policy;
 
-    bitmap_set(dirty_bitmap, ctx->save.p2m_size);
-
     for ( ; ; )
     {
         policy_decision = precopy_policy(*policy_stats, data);
@@ -535,7 +525,7 @@ static int send_memory_live(struct xc_sr
             if ( rc )
                 goto out;
 
-            rc = send_dirty_pages(ctx, stats.dirty_count);
+            rc = send_dirty_pages(ctx, stats.dirty_count, x == 1);
             if ( rc )
                 goto out;
         }
@@ -681,7 +671,8 @@ static int suspend_and_send_dirty(struct
         }
     }
 
-    rc = send_dirty_pages(ctx, stats.dirty_count + 
ctx->save.nr_deferred_pages);
+    rc = send_dirty_pages(ctx, stats.dirty_count + ctx->save.nr_deferred_pages,
+                          false /* all_dirty */);
     if ( rc )
         goto out;
 
@@ -801,8 +792,11 @@ static int setup(struct xc_sr_context *c
     if ( rc )
         goto err;
 
-    dirty_bitmap = xc_hypercall_buffer_alloc_pages(
-        xch, dirty_bitmap, NRPAGES(bitmap_size(ctx->save.p2m_size)));
+    dirty_bitmap = ctx->save.live || ctx->stream_type != XC_STREAM_PLAIN
+        ? xc_hypercall_buffer_alloc_pages(
+              xch, dirty_bitmap, NRPAGES(bitmap_size(ctx->save.p2m_size)))
+        : (void *)-1L;
+
     ctx->save.batch_pfns = malloc(MAX_BATCH_SIZE *
                                   sizeof(*ctx->save.batch_pfns));
     ctx->save.deferred_pages = bitmap_alloc(ctx->save.p2m_size);