[PATCH v9 3/4] libs/guest: allocate various migration arrays just once

[Frediano Ziglio <freddy77@xxxxxxxxx>]

From: Edwin Török <edwin.torok@xxxxxxxxxx>

Allocate these array just once at the start of migration,
using the maximum batch size, and free them at the end.

Signed-off-by: Edwin Török <edwin.torok@xxxxxxxxxx>
Signed-off-by: Frediano Ziglio <frediano.ziglio@xxxxxxxxxx>
---
Changes since v2:
- change prefix in subject.

Changes since v3:
- fix comment style

Changes since v4:
- change order of fields in structure.

Changes since v6:
- split preparation commit.

Changes since v8:
- remove useless memset;
- initialize variables while declaring them.
---
 tools/libs/guest/xg_sr_common.h |  6 +++++
 tools/libs/guest/xg_sr_save.c   | 45 ++++++++++++---------------------
 2 files changed, 22 insertions(+), 29 deletions(-)

diff --git a/tools/libs/guest/xg_sr_common.h b/tools/libs/guest/xg_sr_common.h
index 7574c9f5b6..c07c6db59e 100644
--- a/tools/libs/guest/xg_sr_common.h
+++ b/tools/libs/guest/xg_sr_common.h
@@ -246,6 +246,12 @@ struct xc_sr_context
             struct xc_sr_context_save_buffers
             {
                 xen_pfn_t batch_pfns[MAX_BATCH_SIZE];
+                xen_pfn_t mfns[MAX_BATCH_SIZE];
+                xen_pfn_t types[MAX_BATCH_SIZE];
+                void *local_pages[MAX_BATCH_SIZE];
+                struct iovec iov[MAX_BATCH_SIZE + 2]; /* Headers + data. */
+                uint64_t rec_pfns[MAX_BATCH_SIZE];
+                int errors[MAX_BATCH_SIZE];
             } *buffers;
         } save;
 
diff --git a/tools/libs/guest/xg_sr_save.c b/tools/libs/guest/xg_sr_save.c
index 22348db445..6a77e33a47 100644
--- a/tools/libs/guest/xg_sr_save.c
+++ b/tools/libs/guest/xg_sr_save.c
@@ -86,15 +86,12 @@ static int write_checkpoint_record(struct xc_sr_context 
*ctx)
 static int write_batch(struct xc_sr_context *ctx)
 {
     xc_interface *xch = ctx->xch;
-    xen_pfn_t *mfns = NULL, *types = NULL;
     void *guest_mapping = NULL;
-    void **local_pages = NULL;
-    int *errors = NULL, rc = -1;
+    int rc = -1;
     unsigned int i, p, nr_pages = 0, nr_pages_mapped = 0;
     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;
     xen_pfn_t *const batch_pfns = ctx->save.buffers->batch_pfns;
     struct {
         struct xc_sr_rhdr rec;
@@ -110,28 +107,21 @@ static int write_batch(struct xc_sr_context *ctx)
         },
     };
 
-    assert(nr_pfns != 0);
-    assert(nr_pfns <= MAX_BATCH_SIZE);
-
     /* Mfns of the batch pfns. */
-    mfns = malloc(nr_pfns * sizeof(*mfns));
+    xen_pfn_t *const mfns = ctx->save.buffers->mfns;
     /* Types of the batch pfns. */
-    types = malloc(nr_pfns * sizeof(*types));
+    xen_pfn_t *const types = ctx->save.buffers->types;
     /* Errors from attempting to map the gfns. */
-    errors = malloc(nr_pfns * sizeof(*errors));
+    int *const errors = ctx->save.buffers->errors;
     /* Pointers to locally allocated pages.  Need freeing. */
-    local_pages = calloc(nr_pfns, sizeof(*local_pages));
+    void **const local_pages = ctx->save.buffers->local_pages;
     /* iovec[] for writev(). */
-    iov = malloc((nr_pfns + 2) * sizeof(*iov));
+    struct iovec *const iov = ctx->save.buffers->iov;
     /* page_data record PFNs list */
-    rec_pfns = malloc(nr_pfns * sizeof(*rec_pfns));
+    uint64_t *const rec_pfns = ctx->save.buffers->rec_pfns;
 
-    if ( !mfns || !types || !errors || !local_pages || !iov || !rec_pfns )
-    {
-        ERROR("Unable to allocate arrays for a batch of %u pages",
-              nr_pfns);
-        goto err;
-    }
+    assert(nr_pfns != 0);
+    assert(nr_pfns <= MAX_BATCH_SIZE);
 
     iov[0].iov_base = &hdrs;
     iov[0].iov_len = sizeof(hdrs);
@@ -249,14 +239,11 @@ static int write_batch(struct xc_sr_context *ctx)
  err:
     if ( guest_mapping )
         xenforeignmemory_unmap(xch->fmem, guest_mapping, nr_pages_mapped);
-    for ( i = 0; local_pages && i < nr_pfns; ++i )
+    for ( i = 0; i < nr_pfns; ++i )
+    {
         free(local_pages[i]);
-    free(rec_pfns);
-    free(iov);
-    free(local_pages);
-    free(errors);
-    free(types);
-    free(mfns);
+        local_pages[i] = NULL;
+    }
 
     return rc;
 }
@@ -790,8 +777,8 @@ static int setup(struct xc_sr_context *ctx)
 
     if ( !ctx->save.buffers || !dirty_bitmap || !ctx->save.deferred_pages )
     {
-        ERROR("Unable to allocate memory for dirty bitmaps, batch pfns and"
-              " deferred pages");
+        ERROR("Unable to allocate memory for dirty bitmaps, deferred pages"
+              " and various batch buffers");
         rc = -1;
         errno = ENOMEM;
         goto err;
-- 
2.43.0