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Re: [Qemu-devel] [PATCH 1/1] Count used RAMBlock pages for migration_dir
From: |
陈梁 |
Subject: |
Re: [Qemu-devel] [PATCH 1/1] Count used RAMBlock pages for migration_dirty_pages |
Date: |
Fri, 21 Mar 2014 21:44:57 +0800 |
> From: "Dr. David Alan Gilbert" <address@hidden>
>
> This is a fix for a bug* triggered by a migration after hot unplugging
> a few virtio-net NICs, that caused migration never to converge, because
> 'migration_dirty_pages' is incorrectly initialised.
>
> 'migration_dirty_pages' is used as a tally of the number of outstanding
> dirty pages, to give the migration code an idea of how much more data
> will need to be transferred, and thus whether it can end the iterative
> phase.
>
> It was initialised to the total size of the RAMBlock address space,
> however hotunplug can leave this space sparse, and hence
> migration_dirty_pages ended up too large.
>
> Note that the code tries to be careful when counting to deal with
> RAMBlocks that share the same end/start page - I don't know
> if this is actually possible and it does complicate the code,
> but since there was other code that dealt with unaligned RAMBlocks
> it seemed possible.
>
> Signed-off-by: Dr. David Alan Gilbert <address@hidden>
>
> (* https://bugzilla.redhat.com/show_bug.cgi?id=1074913 )
> ---
> arch_init.c | 41 +++++++++++++++++++++++++++++++++++++----
> 1 file changed, 37 insertions(+), 4 deletions(-)
>
> diff --git a/arch_init.c b/arch_init.c
> index f18f42e..ef0e98d 100644
> --- a/arch_init.c
> +++ b/arch_init.c
> @@ -727,11 +727,8 @@ static void reset_ram_globals(void)
> static int ram_save_setup(QEMUFile *f, void *opaque)
> {
> RAMBlock *block;
> - int64_t ram_pages = last_ram_offset() >> TARGET_PAGE_BITS;
> + int64_t ram_bitmap_pages;
>
> - migration_bitmap = bitmap_new(ram_pages);
> - bitmap_set(migration_bitmap, 0, ram_pages);
> - migration_dirty_pages = ram_pages;
> mig_throttle_on = false;
> dirty_rate_high_cnt = 0;
>
> @@ -770,6 +767,42 @@ static int ram_save_setup(QEMUFile *f, void *opaque)
> bytes_transferred = 0;
> reset_ram_globals();
>
> + ram_bitmap_pages = last_ram_offset() >> TARGET_PAGE_BITS;
> + migration_bitmap = bitmap_new(ram_bitmap_pages);
> + bitmap_set(migration_bitmap, 0, ram_bitmap_pages);
> + /*
> + * Count the total number of pages used by ram blocks. We clear the dirty
> + * bit for the start/end of each ramblock as we go so that we don't
> double
> + * count ramblocks that have overlapping pages - at entry the whole dirty
> + * bitmap is set.
> + */
> + migration_dirty_pages = 0;
> + QTAILQ_FOREACH(block, &ram_list.blocks, next) {
> + uint64_t block_pages = 0;
> + ram_addr_t saddr, eaddr;
> +
> + saddr = block->mr->ram_addr;
> + eaddr = saddr + block->length - 1;
> + saddr /= TARGET_PAGE_SIZE;
> + eaddr /= TARGET_PAGE_SIZE;
> +
> + /* Do the end pages of the range, that might be shared with others */
> + block_pages += test_and_clear_bit(saddr, migration_bitmap);
> + block_pages += test_and_clear_bit(eaddr, migration_bitmap);
> +
> + if ((saddr + 1) < eaddr) {
> + block_pages += eaddr - (saddr + 1);
> + }
> + migration_dirty_pages += block_pages;
> + /*fprintf(stderr, "ram_save_setup: %s s/e=%zx/%zx page s/e=%zx/%zx"
> + " bp=%zu\n",
> + block->idstr, block->mr->ram_addr,
> + block->mr->ram_addr+block->length-1,
> + saddr, eaddr, block_pages); */
> + }
> + /* and set the bits again that got used for our overlap check */
> + bitmap_set(migration_bitmap, 0, ram_bitmap_pages);
maybe it should like this:
bitmap_set(migration_bitmap, 0, last_ram_offset() >> TARGET_PAGE_BITS);
Because there are some space sparse.
> +
> memory_global_dirty_log_start();
> migration_bitmap_sync();
> qemu_mutex_unlock_iothread();
> --
> 1.8.5.3
>
>
Re: [Qemu-devel] [PATCH 1/1] Count used RAMBlock pages for migration_dirty_pages,
陈梁 <=