On Fri, Aug 18, 2017 at 10:18:37AM -0500, Eric Blake wrote:
> On 08/18/2017 08:31 AM, Stefan Hajnoczi wrote:
> > Most qcow2 files are uncompressed so it is wasteful to allocate (32 + 1)
> > * cluster_size + 512 bytes upfront. Allocate s->cluster_cache and
> > s->cluster_data when the first read operation is performance on a
> > compressed cluster.
> >
> > The buffers are freed in .bdrv_close(). .bdrv_open() no longer has any
> > code paths that can allocate these buffers, so remove the free functions
> > in the error code path.
> >
> > Reported-by: Alexey Kardashevskiy <a...@ozlabs.ru>
> > Cc: Kevin Wolf <kw...@redhat.com>
> > Signed-off-by: Stefan Hajnoczi <stefa...@redhat.com>
> > ---
> > Alexey: Does this improve your memory profiling results?
>
> Is this a regression from earlier versions? Likely, it is NOT -rc4
> material, and thus can wait for 2.11; but it should be fine for -stable
> as part of 2.10.1 down the road.
It's not a regression. s->cluster_data was always allocated upfront in
.bdrv_open().
> > +++ b/block/qcow2-cluster.c
> > @@ -1516,6 +1516,23 @@ int qcow2_decompress_cluster(BlockDriverState *bs,
> > uint64_t cluster_offset)
> > nb_csectors = ((cluster_offset >> s->csize_shift) & s->csize_mask)
> > + 1;
> > sector_offset = coffset & 511;
> > csize = nb_csectors * 512 - sector_offset;
> > +
> > + /* Allocate buffers on first decompress operation, most images are
> > + * uncompressed and the memory overhead can be avoided. The
> > buffers
> > + * are freed in .bdrv_close().
> > + */
> > + if (!s->cluster_data) {
> > + /* one more sector for decompressed data alignment */
> > + s->cluster_data = qemu_try_blockalign(bs->file->bs,
> > + QCOW_MAX_CRYPT_CLUSTERS * s->cluster_size + 512);
> > + if (!s->cluster_data) {
> > + return -EIO;
>
> Is -ENOMEM any better than -EIO here?
There is another instance of -ENOMEM in qcow2.c so it seems reasonable
to use the more specific ENOMEM error code.
I'll resend the patch.
Stefan
