On Thu, Nov 15, 2018 at 06:08:00PM +0800, Wei Wang wrote:
> This patch adds an API to clear bits corresponding to guest free pages
> from the dirty bitmap. Spilt the free page block if it crosses the QEMU
> RAMBlock boundary.
>
> Signed-off-by: Wei Wang
> CC: Dr. David Alan Gilbert
> CC: Juan Quintela
> CC: Michael S. Tsirkin
> CC: Peter Xu
> ---
> include/migration/misc.h | 2 ++
> migration/ram.c | 48
>
> 2 files changed, 50 insertions(+)
>
> diff --git a/include/migration/misc.h b/include/migration/misc.h
> index 4ebf24c..113320e 100644
> --- a/include/migration/misc.h
> +++ b/include/migration/misc.h
> @@ -14,11 +14,13 @@
> #ifndef MIGRATION_MISC_H
> #define MIGRATION_MISC_H
>
> +#include "exec/cpu-common.h"
> #include "qemu/notify.h"
>
> /* migration/ram.c */
>
> void ram_mig_init(void);
> +void qemu_guest_free_page_hint(void *addr, size_t len);
>
> /* migration/block.c */
>
> diff --git a/migration/ram.c b/migration/ram.c
> index ef69dbe..229b791 100644
> --- a/migration/ram.c
> +++ b/migration/ram.c
> @@ -3131,6 +3131,54 @@ static void ram_state_resume_prepare(RAMState *rs,
> QEMUFile *out)
> }
>
> /*
> + * This function clears bits of the free pages reported by the caller from
> the
> + * migration dirty bitmap. @addr is the host address corresponding to the
> + * start of the continuous guest free pages, and @len is the total bytes of
> + * those pages.
> + */
> +void qemu_guest_free_page_hint(void *addr, size_t len)
> +{
> +RAMBlock *block;
> +ram_addr_t offset;
> +size_t used_len, start, npages;
> +MigrationState *s = migrate_get_current();
> +
> +/* This function is currently expected to be used during live migration
> */
> +if (!migration_is_setup_or_active(s->state)) {
> +return;
> +}
> +
> +for (; len > 0; len -= used_len) {
> +block = qemu_ram_block_from_host(addr, false, );
> +assert(block);
> +
> +/*
> + * This handles the case that the RAMBlock is resized after the free
> + * page hint is reported.
> + */
> +if (unlikely(offset > block->used_length)) {
> +return;
> +}
Again, is it possible to resize during migration?
So I think the check is fine, but uncertain about the comment.
And shall we print something if that happened? We can use
error_report_once(), and squashing the above assert:
if (!block || offset > block->used_length) {
/* should never happen, but if it happens we ignore the hints and warn */
error_report_once("...");
return;
}
What do you think?
> +
> +if (len <= block->used_length - offset) {
> +used_len = len;
> +} else {
> +used_len = block->used_length - offset;
> +addr += used_len;
Maybe moving this line into the for() could be a bit better?
for (; len > 0; len -= used_len, addr += used_len) {
> +}
> +
> +start = offset >> TARGET_PAGE_BITS;
> +npages = used_len >> TARGET_PAGE_BITS;
> +
> +qemu_mutex_lock(_state->bitmap_mutex);
> +ram_state->migration_dirty_pages -=
> + bitmap_count_one_with_offset(block->bmap, start,
> npages);
> +bitmap_clear(block->bmap, start, npages);
> +qemu_mutex_unlock(_state->bitmap_mutex);
> +}
> +}
> +
> +/*
> * Each of ram_save_setup, ram_save_iterate and ram_save_complete has
> * long-running RCU critical section. When rcu-reclaims in the code
> * start to become numerous it will be necessary to reduce the
> --
> 1.8.3.1
>
Regards,
--
Peter Xu
