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Re: [Qemu-devel] [PATCH v2] cpu_physical_memory_sync_dirty_bitmap: Fix a
From: |
Dr. David Alan Gilbert |
Subject: |
Re: [Qemu-devel] [PATCH v2] cpu_physical_memory_sync_dirty_bitmap: Fix alignment check |
Date: |
Mon, 24 Jul 2017 18:27:18 +0100 |
User-agent: |
Mutt/1.8.3 (2017-05-23) |
* Paolo Bonzini (address@hidden) wrote:
> 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?
Yes please.
Dave
> Paolo
--
Dr. David Alan Gilbert / address@hidden / Manchester, UK