[PATCH v2 15/29] migration/ram: Add support for 'fixed-ram' outgoing migration

[Fabiano Rosas]

From: Nikolay Borisov <nborisov@suse.com>

Implement the outgoing migration side for the 'fixed-ram' capability.

A bitmap is introduced to track which pages have been written in the
migration file. Pages are written at a fixed location for every
ramblock. Zero pages are ignored as they'd be zero in the destination
migration as well.

The migration stream is altered to put the dirty pages for a ramblock
after its header instead of having a sequential stream of pages that
follow the ramblock headers. Since all pages have a fixed location,
RAM_SAVE_FLAG_EOS is no longer generated on every migration iteration.

Without fixed-ram (current):

ramblock 1 header|ramblock 2 header|...|RAM_SAVE_FLAG_EOS|stream of
 pages (iter 1)|RAM_SAVE_FLAG_EOS|stream of pages (iter 2)|...

With fixed-ram (new):

ramblock 1 header|ramblock 1 fixed-ram header|ramblock 1 pages (fixed
 offsets)|ramblock 2 header|ramblock 2 fixed-ram header|ramblock 2
 pages (fixed offsets)|...|RAM_SAVE_FLAG_EOS

where:
 - ramblock header: the generic information for a ramblock, such as
   idstr, used_len, etc.

 - ramblock fixed-ram header: the new information added by this
   feature: bitmap of pages written, bitmap size and offset of pages
   in the migration file.

Signed-off-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: Fabiano Rosas <farosas@suse.de>
---
 include/exec/ramblock.h |  8 ++++
 migration/options.c     |  3 --
 migration/ram.c         | 98 ++++++++++++++++++++++++++++++++++++-----
 3 files changed, 96 insertions(+), 13 deletions(-)

diff --git a/include/exec/ramblock.h b/include/exec/ramblock.h
index 69c6a53902..e0e3f16852 100644
--- a/include/exec/ramblock.h
+++ b/include/exec/ramblock.h
@@ -44,6 +44,14 @@ struct RAMBlock {
     size_t page_size;
     /* dirty bitmap used during migration */
     unsigned long *bmap;
+    /* shadow dirty bitmap used when migrating to a file */
+    unsigned long *shadow_bmap;
+    /*
+     * offset in the file pages belonging to this ramblock are saved,
+     * used only during migration to a file.
+     */
+    off_t bitmap_offset;
+    uint64_t pages_offset;
     /* bitmap of already received pages in postcopy */
     unsigned long *receivedmap;
 
diff --git a/migration/options.c b/migration/options.c
index 2622d8c483..9f693d909f 100644
--- a/migration/options.c
+++ b/migration/options.c
@@ -271,12 +271,9 @@ bool migrate_events(void)
 
 bool migrate_fixed_ram(void)
 {
-/*
     MigrationState *s = migrate_get_current();
 
     return s->capabilities[MIGRATION_CAPABILITY_FIXED_RAM];
-*/
-    return false;
 }
 
 bool migrate_ignore_shared(void)
diff --git a/migration/ram.c b/migration/ram.c
index 92769902bb..152a03604f 100644
--- a/migration/ram.c
+++ b/migration/ram.c
@@ -1157,12 +1157,18 @@ static int save_zero_page(RAMState *rs, 
PageSearchStatus *pss,
         return 0;
     }
 
+    stat64_add(&mig_stats.zero_pages, 1);
+
+    if (migrate_fixed_ram()) {
+        /* zero pages are not transferred with fixed-ram */
+        clear_bit(offset >> TARGET_PAGE_BITS, pss->block->shadow_bmap);
+        return 1;
+    }
+
     len += save_page_header(pss, file, pss->block, offset | 
RAM_SAVE_FLAG_ZERO);
     qemu_put_byte(file, 0);
     len += 1;
     ram_release_page(pss->block->idstr, offset);
-
-    stat64_add(&mig_stats.zero_pages, 1);
     ram_transferred_add(len);
 
     /*
@@ -1220,14 +1226,20 @@ static int save_normal_page(PageSearchStatus *pss, 
RAMBlock *block,
 {
     QEMUFile *file = pss->pss_channel;
 
-    ram_transferred_add(save_page_header(pss, pss->pss_channel, block,
-                                         offset | RAM_SAVE_FLAG_PAGE));
-    if (async) {
-        qemu_put_buffer_async(file, buf, TARGET_PAGE_SIZE,
-                              migrate_release_ram() &&
-                              migration_in_postcopy());
+    if (migrate_fixed_ram()) {
+        qemu_put_buffer_at(file, buf, TARGET_PAGE_SIZE,
+                           block->pages_offset + offset);
+        set_bit(offset >> TARGET_PAGE_BITS, block->shadow_bmap);
     } else {
-        qemu_put_buffer(file, buf, TARGET_PAGE_SIZE);
+        ram_transferred_add(save_page_header(pss, pss->pss_channel, block,
+                                             offset | RAM_SAVE_FLAG_PAGE));
+        if (async) {
+            qemu_put_buffer_async(file, buf, TARGET_PAGE_SIZE,
+                                  migrate_release_ram() &&
+                                  migration_in_postcopy());
+        } else {
+            qemu_put_buffer(file, buf, TARGET_PAGE_SIZE);
+        }
     }
     ram_transferred_add(TARGET_PAGE_SIZE);
     stat64_add(&mig_stats.normal_pages, 1);
@@ -2475,6 +2487,8 @@ static void ram_save_cleanup(void *opaque)
         block->clear_bmap = NULL;
         g_free(block->bmap);
         block->bmap = NULL;
+        g_free(block->shadow_bmap);
+        block->shadow_bmap = NULL;
     }
 
     xbzrle_cleanup();
@@ -2842,6 +2856,7 @@ static void ram_list_init_bitmaps(void)
              */
             block->bmap = bitmap_new(pages);
             bitmap_set(block->bmap, 0, pages);
+            block->shadow_bmap = bitmap_new(block->used_length >> 
TARGET_PAGE_BITS);
             block->clear_bmap_shift = shift;
             block->clear_bmap = bitmap_new(clear_bmap_size(pages, shift));
         }
@@ -2979,6 +2994,44 @@ void qemu_guest_free_page_hint(void *addr, size_t len)
     }
 }
 
+#define FIXED_RAM_HDR_VERSION 1
+struct FixedRamHeader {
+    uint32_t version;
+    uint64_t page_size;
+    uint64_t bitmap_offset;
+    uint64_t pages_offset;
+    /* end of v1 */
+} QEMU_PACKED;
+
+static void fixed_ram_insert_header(QEMUFile *file, RAMBlock *block)
+{
+    g_autofree struct FixedRamHeader *header;
+    size_t header_size, bitmap_size;
+    long num_pages;
+
+    header = g_new0(struct FixedRamHeader, 1);
+    header_size = sizeof(struct FixedRamHeader);
+
+    num_pages = block->used_length >> TARGET_PAGE_BITS;
+    bitmap_size = BITS_TO_LONGS(num_pages) * sizeof(unsigned long);
+
+    /*
+     * Save the file offsets of where the bitmap and the pages should
+     * go as they are written at the end of migration and during the
+     * iterative phase, respectively.
+     */
+    block->bitmap_offset = qemu_get_offset(file) + header_size;
+    block->pages_offset = ROUND_UP(block->bitmap_offset +
+                                   bitmap_size, 0x100000);
+
+    header->version = cpu_to_be32(FIXED_RAM_HDR_VERSION);
+    header->page_size = cpu_to_be64(TARGET_PAGE_SIZE);
+    header->bitmap_offset = cpu_to_be64(block->bitmap_offset);
+    header->pages_offset = cpu_to_be64(block->pages_offset);
+
+    qemu_put_buffer(file, (uint8_t *) header, header_size);
+}
+
 /*
  * Each of ram_save_setup, ram_save_iterate and ram_save_complete has
  * long-running RCU critical section.  When rcu-reclaims in the code
@@ -3028,6 +3081,12 @@ static int ram_save_setup(QEMUFile *f, void *opaque)
             if (migrate_ignore_shared()) {
                 qemu_put_be64(f, block->mr->addr);
             }
+
+            if (migrate_fixed_ram()) {
+                fixed_ram_insert_header(f, block);
+                /* prepare offset for next ramblock */
+                qemu_set_offset(f, block->pages_offset + block->used_length, 
SEEK_SET);
+            }
         }
     }
 
@@ -3061,6 +3120,20 @@ static int ram_save_setup(QEMUFile *f, void *opaque)
     return 0;
 }
 
+static void ram_save_shadow_bmap(QEMUFile *f)
+{
+    RAMBlock *block;
+
+    RAMBLOCK_FOREACH_MIGRATABLE(block) {
+        long num_pages = block->used_length >> TARGET_PAGE_BITS;
+        long bitmap_size = BITS_TO_LONGS(num_pages) * sizeof(unsigned long);
+        qemu_put_buffer_at(f, (uint8_t *)block->shadow_bmap, bitmap_size,
+                           block->bitmap_offset);
+        /* to catch any thread late sending pages */
+        block->shadow_bmap = NULL;
+    }
+}
+
 /**
  * ram_save_iterate: iterative stage for migration
  *
@@ -3179,7 +3252,6 @@ out:
         qemu_put_be64(f, RAM_SAVE_FLAG_EOS);
         qemu_fflush(f);
         ram_transferred_add(8);
-
         ret = qemu_file_get_error(f);
     }
     if (ret < 0) {
@@ -3256,7 +3328,13 @@ static int ram_save_complete(QEMUFile *f, void *opaque)
     if (migrate_multifd() && !migrate_multifd_flush_after_each_section()) {
         qemu_put_be64(f, RAM_SAVE_FLAG_MULTIFD_FLUSH);
     }
+
+    if (migrate_fixed_ram()) {
+        ram_save_shadow_bmap(f);
+    }
+
     qemu_put_be64(f, RAM_SAVE_FLAG_EOS);
+
     qemu_fflush(f);
 
     return 0;
-- 
2.35.3