Re: [Qemu-devel] [Qemu-block] [PATCH 1/6] qcow2: use one single memory block for the L2/refcount cache tables

[Stefan Hajnoczi]

On Mon, May 04, 2015 at 12:58:13PM +0200, Kevin Wolf wrote:
> Am 01.05.2015 um 16:23 hat Stefan Hajnoczi geschrieben:
> > On Thu, Apr 30, 2015 at 01:11:40PM +0300, Alberto Garcia wrote:
> > >  Qcow2Cache *qcow2_cache_create(BlockDriverState *bs, int num_tables)
> > >  {
> > >      BDRVQcowState *s = bs->opaque;
> > >      Qcow2Cache *c;
> > > -    int i;
> > >  
> > >      c = g_new0(Qcow2Cache, 1);
> > >      c->size = num_tables;
> > > +    c->table_size = s->cluster_size;
> > 
> > This assumes c->table_size meets bs' memory alignment requirements.  The
> > following would be safer:
> > 
> > c->table_size = QEMU_ALIGN_UP(c->table_size, bdrv_opt_mem_align(bs->file));
> 
> You can't just access more than one cluster. You might be caching data
> and later write it back when it's stale.

I don't mean I/O alignment, just memory alignment (i.e. the start
address of the data buffer in memory).

Stefan

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