[PATCH v20210713 10/31] tools: save: preallocate iov 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.

Signed-off-by: Olaf Hering <olaf@xxxxxxxxx>
---
 tools/libs/guest/xg_sr_common.h |  1 +
 tools/libs/guest/xg_sr_save.c   | 34 ++++++++++++++++-----------------
 2 files changed, 18 insertions(+), 17 deletions(-)

diff --git a/tools/libs/guest/xg_sr_common.h b/tools/libs/guest/xg_sr_common.h
index d2b838ed33..e2a068bb7e 100644
--- a/tools/libs/guest/xg_sr_common.h
+++ b/tools/libs/guest/xg_sr_common.h
@@ -247,6 +247,7 @@ struct xc_sr_context
             xen_pfn_t *mfns;
             xen_pfn_t *types;
             int *errors;
+            struct iovec *iov;
             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 5b416fda60..92eba456e6 100644
--- a/tools/libs/guest/xg_sr_save.c
+++ b/tools/libs/guest/xg_sr_save.c
@@ -96,7 +96,7 @@ static int write_batch(struct xc_sr_context *ctx)
     unsigned int nr_pfns = ctx->save.nr_batch_pfns;
     void *page, *orig_page;
     uint64_t *rec_pfns = NULL;
-    struct iovec *iov = NULL; int iovcnt = 0;
+    int iovcnt = 0;
     struct xc_sr_rec_page_data_header hdr = { 0 };
     struct xc_sr_record rec = {
         .type = REC_TYPE_PAGE_DATA,
@@ -108,10 +108,8 @@ static int write_batch(struct xc_sr_context *ctx)
     guest_data = calloc(nr_pfns, sizeof(*guest_data));
     /* Pointers to locally allocated pages.  Need freeing. */
     local_pages = calloc(nr_pfns, sizeof(*local_pages));
-    /* iovec[] for writev(). */
-    iov = malloc((nr_pfns + 4) * sizeof(*iov));
 
-    if ( !guest_data || !local_pages || !iov )
+    if ( !guest_data || !local_pages )
     {
         ERROR("Unable to allocate arrays for a batch of %u pages",
               nr_pfns);
@@ -221,17 +219,17 @@ static int write_batch(struct xc_sr_context *ctx)
     for ( i = 0; i < nr_pfns; ++i )
         rec_pfns[i] = ((uint64_t)(ctx->save.types[i]) << 32) | 
ctx->save.batch_pfns[i];
 
-    iov[0].iov_base = &rec.type;
-    iov[0].iov_len = sizeof(rec.type);
+    ctx->save.iov[0].iov_base = &rec.type;
+    ctx->save.iov[0].iov_len = sizeof(rec.type);
 
-    iov[1].iov_base = &rec.length;
-    iov[1].iov_len = sizeof(rec.length);
+    ctx->save.iov[1].iov_base = &rec.length;
+    ctx->save.iov[1].iov_len = sizeof(rec.length);
 
-    iov[2].iov_base = &hdr;
-    iov[2].iov_len = sizeof(hdr);
+    ctx->save.iov[2].iov_base = &hdr;
+    ctx->save.iov[2].iov_len = sizeof(hdr);
 
-    iov[3].iov_base = rec_pfns;
-    iov[3].iov_len = nr_pfns * sizeof(*rec_pfns);
+    ctx->save.iov[3].iov_base = rec_pfns;
+    ctx->save.iov[3].iov_len = nr_pfns * sizeof(*rec_pfns);
 
     iovcnt = 4;
     ctx->save.pages_sent += nr_pages;
@@ -243,15 +241,15 @@ static int write_batch(struct xc_sr_context *ctx)
         {
             if ( guest_data[i] )
             {
-                iov[iovcnt].iov_base = guest_data[i];
-                iov[iovcnt].iov_len = PAGE_SIZE;
+                ctx->save.iov[iovcnt].iov_base = guest_data[i];
+                ctx->save.iov[iovcnt].iov_len = PAGE_SIZE;
                 iovcnt++;
                 --nr_pages;
             }
         }
     }
 
-    if ( writev_exact(ctx->fd, iov, iovcnt) )
+    if ( writev_exact(ctx->fd, ctx->save.iov, iovcnt) )
     {
         PERROR("Failed to write page data to stream");
         goto err;
@@ -267,7 +265,6 @@ static int write_batch(struct xc_sr_context *ctx)
         xenforeignmemory_unmap(xch->fmem, guest_mapping, nr_pages_mapped);
     for ( i = 0; local_pages && i < nr_pfns; ++i )
         free(local_pages[i]);
-    free(iov);
     free(local_pages);
     free(guest_data);
 
@@ -846,10 +843,12 @@ static int setup(struct xc_sr_context *ctx)
     ctx->save.mfns = malloc(MAX_BATCH_SIZE * sizeof(*ctx->save.mfns));
     ctx->save.types = malloc(MAX_BATCH_SIZE * sizeof(*ctx->save.types));
     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.deferred_pages = bitmap_alloc(ctx->save.p2m_size);
 
     if ( !ctx->save.batch_pfns || !ctx->save.mfns || !ctx->save.types ||
-         !ctx->save.errors || !dirty_bitmap || !ctx->save.deferred_pages )
+         !ctx->save.errors || !ctx->save.iov || !dirty_bitmap ||
+         !ctx->save.deferred_pages )
     {
         ERROR("Unable to allocate memory for dirty bitmaps, batch pfns and"
               " deferred pages");
@@ -880,6 +879,7 @@ 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.iov);
     free(ctx->save.errors);
     free(ctx->save.types);
     free(ctx->save.mfns);