[PATCH v20210601 09/38] tools/guest: prepare to allocate arrays once

[Olaf Hering <olaf@xxxxxxxxx>]

The hotpath 'send_dirty_pages' is supposed to do just one thing: sending.
The other end 'handle_page_data' is supposed to do just receiving.

But instead both do other costly work like memory allocations and data moving.
Do the allocations once, the array sizes are a compiletime constant.
Avoid unneeded copying of data by receiving data directly into mapped guest 
memory.

This patch is just prepartion, subsequent changes will populate the arrays.

Once all changes are applied, migration of a busy HVM domU changes like that:

Without this series, from sr650 to sr950 (xen-4.15.20201027T173911.16a20963b3 
xen_testing):
2020-10-29 10:23:10.711+0000: xc: show_transfer_rate: 23663128 bytes + 2879563 
pages in 55.324905335 sec, 203 MiB/sec: Internal error
2020-10-29 10:23:35.115+0000: xc: show_transfer_rate: 16829632 bytes + 2097552 
pages in 24.401179720 sec, 335 MiB/sec: Internal error
2020-10-29 10:23:59.436+0000: xc: show_transfer_rate: 16829032 bytes + 2097478 
pages in 24.319025928 sec, 336 MiB/sec: Internal error
2020-10-29 10:24:23.844+0000: xc: show_transfer_rate: 16829024 bytes + 2097477 
pages in 24.406992500 sec, 335 MiB/sec: Internal error
2020-10-29 10:24:48.292+0000: xc: show_transfer_rate: 16828912 bytes + 2097463 
pages in 24.446489027 sec, 335 MiB/sec: Internal error
2020-10-29 10:25:01.816+0000: xc: show_transfer_rate: 16836080 bytes + 2098356 
pages in 13.447091818 sec, 609 MiB/sec: Internal error

With this series, from sr650 to sr950 (xen-4.15.20201027T173911.16a20963b3 
xen_unstable):
2020-10-28 21:26:05.074+0000: xc: show_transfer_rate: 23663128 bytes + 2879563 
pages in 52.564054368 sec, 213 MiB/sec: Internal error
2020-10-28 21:26:23.527+0000: xc: show_transfer_rate: 16830040 bytes + 2097603 
pages in 18.450592015 sec, 444 MiB/sec: Internal error
2020-10-28 21:26:41.926+0000: xc: show_transfer_rate: 16830944 bytes + 2097717 
pages in 18.397862306 sec, 445 MiB/sec: Internal error
2020-10-28 21:27:00.339+0000: xc: show_transfer_rate: 16829176 bytes + 2097498 
pages in 18.411973339 sec, 445 MiB/sec: Internal error
2020-10-28 21:27:18.643+0000: xc: show_transfer_rate: 16828592 bytes + 2097425 
pages in 18.303326695 sec, 447 MiB/sec: Internal error
2020-10-28 21:27:26.289+0000: xc: show_transfer_rate: 16835952 bytes + 2098342 
pages in 7.579846749 sec, 1081 MiB/sec: Internal error

Signed-off-by: Olaf Hering <olaf@xxxxxxxxx>
---
 tools/libs/saverestore/common.h  | 8 ++++++++
 tools/libs/saverestore/restore.c | 8 ++++++++
 tools/libs/saverestore/save.c    | 4 +++-
 3 files changed, 19 insertions(+), 1 deletion(-)

diff --git a/tools/libs/saverestore/common.h b/tools/libs/saverestore/common.h
index f5fe23caad..80b2e878aa 100644
--- a/tools/libs/saverestore/common.h
+++ b/tools/libs/saverestore/common.h
@@ -223,6 +223,12 @@ static inline int update_blob(struct xc_sr_blob *blob,
     return 0;
 }
 
+struct xc_sr_save_arrays {
+};
+
+struct xc_sr_restore_arrays {
+};
+
 struct xc_sr_context
 {
     xc_interface *xch;
@@ -260,6 +266,7 @@ struct xc_sr_context
             unsigned long *deferred_pages;
             unsigned long nr_deferred_pages;
             xc_hypercall_buffer_t dirty_bitmap_hbuf;
+            struct xc_sr_save_arrays *m;
         } save;
 
         struct /* Restore data. */
@@ -311,6 +318,7 @@ struct xc_sr_context
 
             /* Sender has invoked verify mode on the stream. */
             bool verify;
+            struct xc_sr_restore_arrays *m;
         } restore;
     };
 
diff --git a/tools/libs/saverestore/restore.c b/tools/libs/saverestore/restore.c
index 700f9e74b5..a6cf9ee41c 100644
--- a/tools/libs/saverestore/restore.c
+++ b/tools/libs/saverestore/restore.c
@@ -739,6 +739,13 @@ static int setup(struct xc_sr_context *ctx)
     }
     ctx->restore.allocated_rec_num = DEFAULT_BUF_RECORDS;
 
+    ctx->restore.m = malloc(sizeof(*ctx->restore.m));
+    if ( !ctx->restore.m ) {
+        ERROR("Unable to allocate memory for arrays");
+        rc = -1;
+        goto err;
+    }
+
  err:
     return rc;
 }
@@ -757,6 +764,7 @@ static void cleanup(struct xc_sr_context *ctx)
         xc_hypercall_buffer_free_pages(
             xch, dirty_bitmap, NRPAGES(bitmap_size(ctx->restore.p2m_size)));
 
+    free(ctx->restore.m);
     free(ctx->restore.buffered_records);
     free(ctx->restore.populated_pfns);
 
diff --git a/tools/libs/saverestore/save.c b/tools/libs/saverestore/save.c
index 760ca04a84..1662e3ee50 100644
--- a/tools/libs/saverestore/save.c
+++ b/tools/libs/saverestore/save.c
@@ -853,8 +853,9 @@ static int setup(struct xc_sr_context *ctx)
     ctx->save.batch_pfns = malloc(MAX_BATCH_SIZE *
                                   sizeof(*ctx->save.batch_pfns));
     ctx->save.deferred_pages = bitmap_alloc(ctx->save.p2m_size);
+    ctx->save.m = malloc(sizeof(*ctx->save.m));
 
-    if ( !ctx->save.batch_pfns || !dirty_bitmap || !ctx->save.deferred_pages )
+    if ( !ctx->save.m || !ctx->save.batch_pfns || !dirty_bitmap || 
!ctx->save.deferred_pages )
     {
         ERROR("Unable to allocate memory for dirty bitmaps, batch pfns and"
               " deferred pages");
@@ -886,6 +887,7 @@ static void cleanup(struct xc_sr_context *ctx)
                                    NRPAGES(bitmap_size(ctx->save.p2m_size)));
     free(ctx->save.deferred_pages);
     free(ctx->save.batch_pfns);
+    free(ctx->save.m);
 }
 
 /*