On Mon, Oct 23, 2023 at 05:35:54PM -0300, Fabiano Rosas wrote:
> 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):
>
> 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 <nbori...@suse.com>
> Signed-off-by: Fabiano Rosas <faro...@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);
Here we keep zero page accounting, but..
> +
> + 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));
.. here we ignored normal page accounting.
I think we should have the same behavior on both, perhaps keep them always?
> + 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);
AFAICT bmap should also use used_length. How about adding one more patch
to change that, then you can use "pages" here?
See ram_mig_ram_block_resized() where we call migration_cancel() if resized.
> 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);
This is the "page size" for the shadow bitmap, right? Shall we state it
somewhere (e.g. explaining why it's not block->page_size)?
It's unfortunate that we already have things like:
if (migrate_postcopy_ram() && block->page_size !=
qemu_host_page_size) {
qemu_put_be64(f, block->page_size);
}
But indeed we can't merge them because they seem to service different
purpose.
> + 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;
What is this for? Wouldn't this leak the buffer already?
> + }
> +}
> +
> /**
> * 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
>
--
Peter Xu
