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Re: [Qemu-devel] [PATCH v2] cpu_physical_memory_sync_dirty_bitmap: Fix a
From: |
Paolo Bonzini |
Subject: |
Re: [Qemu-devel] [PATCH v2] cpu_physical_memory_sync_dirty_bitmap: Fix alignment check |
Date: |
Mon, 24 Jul 2017 19:09:09 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.2.1 |
On 24/07/2017 18:51, Dr. David Alan Gilbert (git) wrote:
> From: Dr. David Alan Gilbert <address@hidden>
>
> This code has an optimised, word aligned version, and a boring
> unaligned version. Recently 084140bd498909 fixed a missing offset
> addition from the core of both versions. However, the offset isn't
> necessarily aligned and thus the choice between the two versions
> needs fixing up to also include the offset.
>
> Symptom:
> A few stuck unsent pages during migration; not normally noticed
> unless under very low bandwidth in which case the migration may get
> stuck never ending and never performing a 2nd sync; noticed by
> a hanging postcopy-test on a very heavily loaded system.
>
> Fixes: 084140bd498909
>
> Signed-off-by: Dr. David Alan Gilbert <address@hidden>
> Reported-by: Alex BenneƩ <address@hidden>
> Tested-by: Alex BenneƩ <address@hidden>
>
> --
> v2
> Move 'page' inside the if (Comment from Paolo)
> ---
> include/exec/ram_addr.h | 7 ++++---
> 1 file changed, 4 insertions(+), 3 deletions(-)
>
> diff --git a/include/exec/ram_addr.h b/include/exec/ram_addr.h
> index c04f4f67f6..d017639f7e 100644
> --- a/include/exec/ram_addr.h
> +++ b/include/exec/ram_addr.h
> @@ -377,19 +377,20 @@ uint64_t cpu_physical_memory_sync_dirty_bitmap(RAMBlock
> *rb,
> uint64_t *real_dirty_pages)
> {
> ram_addr_t addr;
> - unsigned long page = BIT_WORD(start >> TARGET_PAGE_BITS);
> + unsigned long word = BIT_WORD((start + rb->offset) >> TARGET_PAGE_BITS);
> uint64_t num_dirty = 0;
> unsigned long *dest = rb->bmap;
>
> /* start address is aligned at the start of a word? */
> - if (((page * BITS_PER_LONG) << TARGET_PAGE_BITS) == start) {
> + if (((word * BITS_PER_LONG) << TARGET_PAGE_BITS) ==
> + (start + rb->offset)) {
> int k;
> int nr = BITS_TO_LONGS(length >> TARGET_PAGE_BITS);
> unsigned long * const *src;
> - unsigned long word = BIT_WORD((start + rb->offset) >>
> TARGET_PAGE_BITS);
> unsigned long idx = (word * BITS_PER_LONG) / DIRTY_MEMORY_BLOCK_SIZE;
> unsigned long offset = BIT_WORD((word * BITS_PER_LONG) %
> DIRTY_MEMORY_BLOCK_SIZE);
> + unsigned long page = BIT_WORD(start >> TARGET_PAGE_BITS);
>
> rcu_read_lock();
>
>
Thanks, do you want me to queue this patch?
Paolo