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.
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
Signed-off-by: Fabiano Rosas
---
include/exec/ramblock.h | 13
migration/ram.c | 131 +---
2 files changed, 135 insertions(+), 9 deletions(-)
diff --git a/include/exec/ramblock.h b/include/exec/ramblock.h
index 3eb79723c6..6a66301219 100644
--- a/include/exec/ramblock.h
+++ b/include/exec/ramblock.h
@@ -44,6 +44,19 @@ struct RAMBlock {
size_t page_size;
/* dirty bitmap used during migration */
unsigned long *bmap;
+
+/*
+ * Below fields are only used by fixed-ram migration
+ */
+/* bitmap of pages present in the migration file */
+unsigned long *file_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 4649a81204..84c531722c 100644
--- a/migration/ram.c
+++ b/migration/ram.c
@@ -94,6 +94,18 @@
#define RAM_SAVE_FLAG_MULTIFD_FLUSH0x200
/* 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 0x10
+
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->file_bmap);
+return 1;
+}
+
len += save_page_header(pss, file, pss->block, offset |
RAM_SAVE_FLAG_ZERO);
