From: Nikolay Borisov <nbori...@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): With fixed-ram (new):
--------------------- --------------------------------
| ramblock 1 header | | ramblock 1 header |
--------------------- --------------------------------
| ramblock 2 header | | ramblock 1 fixed-ram header |
--------------------- --------------------------------
| ... | | padding to next 1MB boundary |
--------------------- | ... |
| ramblock n header | --------------------------------
--------------------- | ramblock 1 pages |
| RAM_SAVE_FLAG_EOS | | ... |
--------------------- --------------------------------
| stream of pages | | ramblock 2 header |
| (iter 1) | --------------------------------
| ... | | ramblock 2 fixed-ram header |
--------------------- --------------------------------
| RAM_SAVE_FLAG_EOS | | padding to next 1MB boundary |
--------------------- | ... |
| stream of pages | --------------------------------
| (iter 2) | | ramblock 2 pages |
| ... | | ... |
--------------------- --------------------------------
| ... | | ... |
--------------------- --------------------------------
| 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 <nbori...@suse.com>
Signed-off-by: Fabiano Rosas <faro...@suse.de>
---
- used a macro for alignment value
- documented alignment assumptions
- moved shadow_bmap debug code to multifd patch
- did NOT use used_length for bmap, it breaks dirty page tracking somehow
- uncommented the capability enabling
- accounted for the bitmap size with ram_transferred_add()
---
include/exec/ramblock.h | 8 +++
migration/ram.c | 121 +++++++++++++++++++++++++++++++++++++---
2 files changed, 120 insertions(+), 9 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/ram.c b/migration/ram.c
index 8c7886ab79..4a0ab8105f 100644
--- a/migration/ram.c
+++ b/migration/ram.c
@@ -94,6 +94,18 @@
#define RAM_SAVE_FLAG_MULTIFD_FLUSH 0x200
/* We can't use any flag that is bigger than 0x200 */
+/*
+ * fixed-ram migration supports O_DIRECT, so we need to make sure the
+ * userspace buffer, the IO operation size and the file offset are
+ * aligned according to the underlying device's block size. The first
+ * two are already aligned to page size, but we need to add padding to
+ * the file to align the offset. We cannot read the block size
+ * dynamically because the migration file can be moved between
+ * different systems, so use 1M to cover most block sizes and to keep
+ * the file offset aligned at page size as well.
+ */
+#define FIXED_RAM_FILE_OFFSET_ALIGNMENT 0x100000
+
XBZRLECacheStats xbzrle_counters;
/* used by the search for pages to send */
@@ -1127,12 +1139,18 @@ 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);
/*
@@ -1190,14 +1208,20 @@ 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);
@@ -2413,6 +2437,8 @@ 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();
@@ -2780,6 +2806,7 @@ static void ram_list_init_bitmaps(void)
*/
block->bmap = bitmap_new(pages);
bitmap_set(block->bmap, 0, pages);
+ block->shadow_bmap = bitmap_new(pages);
block->clear_bmap_shift = shift;
block->clear_bmap = bitmap_new(clear_bmap_size(pages, shift));
}
@@ -2917,6 +2944,58 @@ void qemu_guest_free_page_hint(void *addr, size_t len)
}
}
+#define FIXED_RAM_HDR_VERSION 1
+struct FixedRamHeader {
+ uint32_t version;
+ /*
+ * The target's page size, so we know how many pages are in the
+ * bitmap.
+ */
+ uint64_t page_size;
+ /*
+ * The offset in the migration file where the pages bitmap is
+ * found.
+ */
+ uint64_t bitmap_offset;
+ /*
+ * The offset in the migration file where the actual pages (data)
+ * are found.
+ */
+ uint64_t pages_offset;
+ /* end of v1 */
+} QEMU_PACKED;
+typedef struct FixedRamHeader FixedRamHeader;
+
+static void fixed_ram_insert_header(QEMUFile *file, RAMBlock *block)
+{
+ g_autofree FixedRamHeader *header;
+ size_t header_size, bitmap_size;
+ long num_pages;
+
+ header = g_new0(FixedRamHeader, 1);
+ header_size = sizeof(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,
+ FIXED_RAM_FILE_OFFSET_ALIGNMENT);
+
+ 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
@@ -2966,6 +3045,13 @@ 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);
+ }
}
}
@@ -2999,6 +3085,19 @@ static int ram_save_setup(QEMUFile *f, void *opaque)
return qemu_fflush(f);
}
+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);
+ ram_transferred_add(bitmap_size);
+ }
+}
+
/**
* ram_save_iterate: iterative stage for migration
*
@@ -3188,6 +3287,10 @@ static int ram_save_complete(QEMUFile *f, void *opaque)
return ret;
}
+ if (migrate_fixed_ram()) {
+ ram_save_shadow_bmap(f);
+ }
+
if (migrate_multifd() && !migrate_multifd_flush_after_each_section()) {
qemu_put_be64(f, RAM_SAVE_FLAG_MULTIFD_FLUSH);
}
--
2.35.3
