xen/libxc-sr-save-mfns.patch

From: Olaf Hering <olaf@aepfle.de>
Date: Fri, 23 Oct 2020 11:20:36 +0200
Subject: libxc sr save mfns

tools: save: preallocate mfns array

Remove repeated allocation from migration loop. There will never be
more than MAX_BATCH_SIZE pages to process in a batch, see add_to_batch.
Allocate the space once.

Signed-off-by: Olaf Hering <olaf@aepfle.de>
---
 tools/libs/guest/xg_sr_common.h |  1 +
 tools/libs/guest/xg_sr_save.c   | 25 +++++++++++++------------
 2 files changed, 14 insertions(+), 12 deletions(-)

--- a/tools/libs/guest/xg_sr_common.h
+++ b/tools/libs/guest/xg_sr_common.h
@@ -244,6 +244,7 @@ struct xc_sr_context
             struct precopy_stats stats;
 
             xen_pfn_t *batch_pfns;
+            xen_pfn_t *mfns;
             unsigned int nr_batch_pfns;
             unsigned long *deferred_pages;
             unsigned long nr_deferred_pages;
--- a/tools/libs/guest/xg_sr_save.c
+++ b/tools/libs/guest/xg_sr_save.c
@@ -88,7 +88,7 @@ static int write_checkpoint_record(struc
 static int write_batch(struct xc_sr_context *ctx)
 {
     xc_interface *xch = ctx->xch;
-    xen_pfn_t *mfns = NULL, *types = NULL;
+    xen_pfn_t *types = NULL;
     void *guest_mapping = NULL;
     void **guest_data = NULL;
     void **local_pages = NULL;
@@ -105,8 +105,6 @@ static int write_batch(struct xc_sr_cont
 
     assert(nr_pfns != 0);
 
-    /* Mfns of the batch pfns. */
-    mfns = malloc(nr_pfns * sizeof(*mfns));
     /* Types of the batch pfns. */
     types = malloc(nr_pfns * sizeof(*types));
     /* Errors from attempting to map the gfns. */
@@ -118,7 +116,7 @@ static int write_batch(struct xc_sr_cont
     /* iovec[] for writev(). */
     iov = malloc((nr_pfns + 4) * sizeof(*iov));
 
-    if ( !mfns || !types || !errors || !guest_data || !local_pages || !iov )
+    if ( !types || !errors || !guest_data || !local_pages || !iov )
     {
         ERROR("Unable to allocate arrays for a batch of %u pages",
               nr_pfns);
@@ -127,11 +125,11 @@ static int write_batch(struct xc_sr_cont
 
     for ( i = 0; i < nr_pfns; ++i )
     {
-        types[i] = mfns[i] = ctx->save.ops.pfn_to_gfn(ctx,
+        types[i] = ctx->save.mfns[i] = ctx->save.ops.pfn_to_gfn(ctx,
                                                       ctx->save.batch_pfns[i]);
 
         /* Likely a ballooned page. */
-        if ( mfns[i] == INVALID_MFN )
+        if ( ctx->save.mfns[i] == INVALID_MFN )
         {
             set_bit(ctx->save.batch_pfns[i], ctx->save.deferred_pages);
             ++ctx->save.nr_deferred_pages;
@@ -150,20 +148,21 @@ static int write_batch(struct xc_sr_cont
     {
         if ( !is_known_page_type(types[i]) )
         {
-            ERROR("Unknown type %#"PRIpfn" for pfn %#"PRIpfn, types[i], mfns[i]);
+            ERROR("Unknown type %#"PRIpfn" for pfn %#"PRIpfn,
+                  types[i], ctx->save.mfns[i]);
             goto err;
         }
 
         if ( !page_type_has_stream_data(types[i]) )
             continue;
 
-        mfns[nr_pages++] = mfns[i];
+        ctx->save.mfns[nr_pages++] = ctx->save.mfns[i];
     }
 
     if ( nr_pages > 0 )
     {
         guest_mapping = xenforeignmemory_map(
-            xch->fmem, ctx->domid, PROT_READ, nr_pages, mfns, errors);
+            xch->fmem, ctx->domid, PROT_READ, nr_pages, ctx->save.mfns, errors);
         if ( !guest_mapping )
         {
             PERROR("Failed to map guest pages");
@@ -179,7 +178,7 @@ static int write_batch(struct xc_sr_cont
             if ( errors[p] )
             {
                 ERROR("Mapping of pfn %#"PRIpfn" (mfn %#"PRIpfn") failed %d",
-                      ctx->save.batch_pfns[i], mfns[p], errors[p]);
+                      ctx->save.batch_pfns[i], ctx->save.mfns[p], errors[p]);
                 goto err;
             }
 
@@ -277,7 +276,6 @@ static int write_batch(struct xc_sr_cont
     free(guest_data);
     free(errors);
     free(types);
-    free(mfns);
 
     return rc;
 }
@@ -850,9 +848,11 @@ static int setup(struct xc_sr_context *c
         xch, dirty_bitmap, NRPAGES(bitmap_size(ctx->save.p2m_size)));
     ctx->save.batch_pfns = malloc(MAX_BATCH_SIZE *
                                   sizeof(*ctx->save.batch_pfns));
+    ctx->save.mfns = malloc(MAX_BATCH_SIZE * sizeof(*ctx->save.mfns));
     ctx->save.deferred_pages = bitmap_alloc(ctx->save.p2m_size);
 
-    if ( !ctx->save.batch_pfns || !dirty_bitmap || !ctx->save.deferred_pages )
+    if ( !ctx->save.batch_pfns || !ctx->save.mfns ||
+         !dirty_bitmap || !ctx->save.deferred_pages )
     {
         ERROR("Unable to allocate memory for dirty bitmaps, batch pfns and"
               " deferred pages");
@@ -883,6 +883,7 @@ static void cleanup(struct xc_sr_context
     xc_hypercall_buffer_free_pages(xch, dirty_bitmap,
                                    NRPAGES(bitmap_size(ctx->save.p2m_size)));
     free(ctx->save.deferred_pages);
+    free(ctx->save.mfns);
     free(ctx->save.batch_pfns);
 }