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migration/ram: Add outgoing 'mapped-ram' migration

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Implement the outgoing migration side for the 'mapped-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 mapped-ram (current):        With mapped-ram (new):

 ---------------------               --------------------------------
 | ramblock 1 header |               | ramblock 1 header            |
 ---------------------               --------------------------------
 | ramblock 2 header |               | ramblock 1 mapped-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 mapped-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 mapped-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>
Reviewed-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Fabiano Rosas <farosas@suse.de>
Link: https://lore.kernel.org/r/20240229153017.2221-10-farosas@suse.de
Signed-off-by: Peter Xu <peterx@redhat.com>
This commit is contained in:
Fabiano Rosas 2024-02-29 12:30:03 -03:00 committed by Peter Xu
parent 8d9e0d4100
commit c2d5c4a7cb
2 changed files with 135 additions and 9 deletions
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13
include/exec/ramblock.h
View File

@ -44,6 +44,19 @@ struct RAMBlock {
size_t page_size;
/* dirty bitmap used during migration */
unsigned long *bmap;
/*
* Below fields are only used by mapped-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;

131
migration/ram.c
View File

@ -94,6 +94,18 @@
#define RAM_SAVE_FLAG_MULTIFD_FLUSH 0x200
/* We can't use any flag that is bigger than 0x200 */
/*
* mapped-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 MAPPED_RAM_FILE_OFFSET_ALIGNMENT 0x100000
XBZRLECacheStats xbzrle_counters;
/* used by the search for pages to send */
@ -1126,12 +1138,18 @@ static int save_zero_page(RAMState *rs, PageSearchStatus *pss,
return 0;
}
stat64_add(&mig_stats.zero_pages, 1);
if (migrate_mapped_ram()) {
/* zero pages are not transferred with mapped-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);
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);
/*
@ -1189,14 +1207,20 @@ 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_mapped_ram()) {
qemu_put_buffer_at(file, buf, TARGET_PAGE_SIZE,
block->pages_offset + offset);
set_bit(offset >> TARGET_PAGE_BITS, block->file_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);
@ -2411,6 +2435,8 @@ static void ram_save_cleanup(void *opaque)
block->clear_bmap = NULL;
g_free(block->bmap);
block->bmap = NULL;
g_free(block->file_bmap);
block->file_bmap = NULL;
}
xbzrle_cleanup();
@ -2778,6 +2804,9 @@ static void ram_list_init_bitmaps(void)
*/
block->bmap = bitmap_new(pages);
bitmap_set(block->bmap, 0, pages);
if (migrate_mapped_ram()) {
block->file_bmap = bitmap_new(pages);
}
block->clear_bmap_shift = shift;
block->clear_bmap = bitmap_new(clear_bmap_size(pages, shift));
}
@ -2915,6 +2944,60 @@ void qemu_guest_free_page_hint(void *addr, size_t len)
}
}
#define MAPPED_RAM_HDR_VERSION 1
struct MappedRamHeader {
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
* stored.
*/
uint64_t bitmap_offset;
/*
* The offset in the migration file where the actual pages (data)
* are stored.
*/
uint64_t pages_offset;
} QEMU_PACKED;
typedef struct MappedRamHeader MappedRamHeader;
static void mapped_ram_setup_ramblock(QEMUFile *file, RAMBlock *block)
{
g_autofree MappedRamHeader *header = NULL;
size_t header_size, bitmap_size;
long num_pages;
header = g_new0(MappedRamHeader, 1);
header_size = sizeof(MappedRamHeader);
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,
MAPPED_RAM_FILE_OFFSET_ALIGNMENT);
header->version = cpu_to_be32(MAPPED_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);
/* prepare offset for next ramblock */
qemu_set_offset(file, block->pages_offset + block->used_length, SEEK_SET);
}
/*
* Each of ram_save_setup, ram_save_iterate and ram_save_complete has
* long-running RCU critical section. When rcu-reclaims in the code
@ -2964,6 +3047,10 @@ static int ram_save_setup(QEMUFile *f, void *opaque)
if (migrate_ignore_shared()) {
qemu_put_be64(f, block->mr->addr);
}
if (migrate_mapped_ram()) {
mapped_ram_setup_ramblock(f, block);
}
}
}
@ -2997,6 +3084,20 @@ static int ram_save_setup(QEMUFile *f, void *opaque)
return qemu_fflush(f);
}
static void ram_save_file_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->file_bmap, bitmap_size,
block->bitmap_offset);
ram_transferred_add(bitmap_size);
}
}
/**
* ram_save_iterate: iterative stage for migration
*
@ -3186,6 +3287,18 @@ static int ram_save_complete(QEMUFile *f, void *opaque)
return ret;
}
if (migrate_mapped_ram()) {
ram_save_file_bmap(f);
if (qemu_file_get_error(f)) {
Error *local_err = NULL;
int err = qemu_file_get_error_obj(f, &local_err);
error_reportf_err(local_err, "Failed to write bitmap to file: ");
return -err;
}
}
if (migrate_multifd() && !migrate_multifd_flush_after_each_section()) {
qemu_put_be64(f, RAM_SAVE_FLAG_MULTIFD_FLUSH);
}