[PATCH v20210713 12/31] tools: save: preallocate guest_data array

[Olaf Hering <olaf@xxxxxxxxx>]

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

Because this was allocated with calloc:
Adjust the loop to clear unused entries as needed.

Signed-off-by: Olaf Hering <olaf@xxxxxxxxx>
---
 tools/libs/guest/xg_sr_common.h |  1 +
 tools/libs/guest/xg_sr_save.c   | 20 +++++++++++---------
 2 files changed, 12 insertions(+), 9 deletions(-)

diff --git a/tools/libs/guest/xg_sr_common.h b/tools/libs/guest/xg_sr_common.h
index b054661897..b90b35e564 100644
--- a/tools/libs/guest/xg_sr_common.h
+++ b/tools/libs/guest/xg_sr_common.h
@@ -249,6 +249,7 @@ struct xc_sr_context
             int *errors;
             struct iovec *iov;
             uint64_t *rec_pfns;
+            void **guest_data;
             unsigned int nr_batch_pfns;
             unsigned long *deferred_pages;
             unsigned long nr_deferred_pages;
diff --git a/tools/libs/guest/xg_sr_save.c b/tools/libs/guest/xg_sr_save.c
index 7c417f4a2a..0ab8b7205c 100644
--- a/tools/libs/guest/xg_sr_save.c
+++ b/tools/libs/guest/xg_sr_save.c
@@ -89,7 +89,6 @@ static int write_batch(struct xc_sr_context *ctx)
 {
     xc_interface *xch = ctx->xch;
     void *guest_mapping = NULL;
-    void **guest_data = NULL;
     void **local_pages = NULL;
     int rc = -1;
     unsigned int i, p, nr_pages = 0, nr_pages_mapped = 0;
@@ -103,12 +102,10 @@ static int write_batch(struct xc_sr_context *ctx)
 
     assert(nr_pfns != 0);
 
-    /* Pointers to page data to send.  Mapped gfns or local allocations. */
-    guest_data = calloc(nr_pfns, sizeof(*guest_data));
     /* Pointers to locally allocated pages.  Need freeing. */
     local_pages = calloc(nr_pfns, sizeof(*local_pages));
 
-    if ( !guest_data || !local_pages )
+    if ( !local_pages )
     {
         ERROR("Unable to allocate arrays for a batch of %u pages",
               nr_pfns);
@@ -165,7 +162,10 @@ static int write_batch(struct xc_sr_context *ctx)
         for ( i = 0, p = 0; i < nr_pfns; ++i )
         {
             if ( !page_type_has_stream_data(ctx->save.types[i]) )
+            {
+                ctx->save.guest_data[i] = NULL;
                 continue;
+            }
 
             if ( ctx->save.errors[p] )
             {
@@ -183,6 +183,7 @@ static int write_batch(struct xc_sr_context *ctx)
 
             if ( rc )
             {
+                ctx->save.guest_data[i] = NULL;
                 if ( rc == -1 && errno == EAGAIN )
                 {
                     set_bit(ctx->save.batch_pfns[i], ctx->save.deferred_pages);
@@ -194,7 +195,7 @@ static int write_batch(struct xc_sr_context *ctx)
                     goto err;
             }
             else
-                guest_data[i] = page;
+                ctx->save.guest_data[i] = page;
 
             rc = -1;
             ++p;
@@ -232,9 +233,9 @@ static int write_batch(struct xc_sr_context *ctx)
     {
         for ( i = 0; i < nr_pfns; ++i )
         {
-            if ( guest_data[i] )
+            if ( ctx->save.guest_data[i] )
             {
-                ctx->save.iov[iovcnt].iov_base = guest_data[i];
+                ctx->save.iov[iovcnt].iov_base = ctx->save.guest_data[i];
                 ctx->save.iov[iovcnt].iov_len = PAGE_SIZE;
                 iovcnt++;
                 --nr_pages;
@@ -258,7 +259,6 @@ static int write_batch(struct xc_sr_context *ctx)
     for ( i = 0; local_pages && i < nr_pfns; ++i )
         free(local_pages[i]);
     free(local_pages);
-    free(guest_data);
 
     return rc;
 }
@@ -837,11 +837,12 @@ static int setup(struct xc_sr_context *ctx)
     ctx->save.errors = malloc(MAX_BATCH_SIZE * sizeof(*ctx->save.errors));
     ctx->save.iov = malloc((4 + MAX_BATCH_SIZE) * sizeof(*ctx->save.iov));
     ctx->save.rec_pfns = malloc(MAX_BATCH_SIZE * sizeof(*ctx->save.rec_pfns));
+    ctx->save.guest_data = malloc(MAX_BATCH_SIZE * 
sizeof(*ctx->save.guest_data));
     ctx->save.deferred_pages = bitmap_alloc(ctx->save.p2m_size);
 
     if ( !ctx->save.batch_pfns || !ctx->save.mfns || !ctx->save.types ||
          !ctx->save.errors || !ctx->save.iov || !ctx->save.rec_pfns ||
-         !dirty_bitmap || !ctx->save.deferred_pages )
+         !ctx->save.guest_data ||!dirty_bitmap || !ctx->save.deferred_pages )
     {
         ERROR("Unable to allocate memory for dirty bitmaps, batch pfns and"
               " deferred pages");
@@ -872,6 +873,7 @@ static void cleanup(struct xc_sr_context *ctx)
     xc_hypercall_buffer_free_pages(xch, dirty_bitmap,
                                    NRPAGES(bitmap_size(ctx->save.p2m_size)));
     free(ctx->save.deferred_pages);
+    free(ctx->save.guest_data);
     free(ctx->save.rec_pfns);
     free(ctx->save.iov);
     free(ctx->save.errors);