diff mbox

qcow2: allocate cluster_cache/cluster_data on demand

Message ID 20170818133118.8650-1-stefanha@redhat.com (mailing list archive)
State New, archived
Headers show

Commit Message

Stefan Hajnoczi Aug. 18, 2017, 1:31 p.m. UTC
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 <aik@ozlabs.ru>
Cc: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
Alexey: Does this improve your memory profiling results?

 block/qcow2-cluster.c | 17 +++++++++++++++++
 block/qcow2.c         | 12 ------------
 2 files changed, 17 insertions(+), 12 deletions(-)

Comments

Eric Blake Aug. 18, 2017, 3:18 p.m. UTC | #1
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 <aik@ozlabs.ru>
> Cc: Kevin Wolf <kwolf@redhat.com>
> Signed-off-by: Stefan Hajnoczi <stefanha@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.

> +++ 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?
Alexey Kardashevskiy Aug. 19, 2017, 1:01 a.m. UTC | #2
On 18/08/17 23:31, 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 <aik@ozlabs.ru>
> Cc: Kevin Wolf <kwolf@redhat.com>
> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
> ---
> Alexey: Does this improve your memory profiling results?

Yes, it does:

was:
12.81% (1,023,193,088B)
now:
05.36% (393,893,888B)


Tested-by: Alexey Kardashevskiy <aik@ozlabs.ru>

>  block/qcow2-cluster.c | 17 +++++++++++++++++
>  block/qcow2.c         | 12 ------------
>  2 files changed, 17 insertions(+), 12 deletions(-)
> 
> diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c
> index f06c08f64c..c47600a44e 100644
> --- a/block/qcow2-cluster.c
> +++ 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;
> +            }
> +        }
> +        if (!s->cluster_cache) {
> +            s->cluster_cache = g_malloc(s->cluster_size);
> +        }
> +
>          BLKDBG_EVENT(bs->file, BLKDBG_READ_COMPRESSED);
>          ret = bdrv_read(bs->file, coffset >> 9, s->cluster_data,
>                          nb_csectors);
> diff --git a/block/qcow2.c b/block/qcow2.c
> index 40ba26c111..0ac201910a 100644
> --- a/block/qcow2.c
> +++ b/block/qcow2.c
> @@ -1360,16 +1360,6 @@ static int qcow2_do_open(BlockDriverState *bs, QDict *options, int flags,
>          goto fail;
>      }
>  
> -    s->cluster_cache = g_malloc(s->cluster_size);
> -    /* 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 == NULL) {
> -        error_setg(errp, "Could not allocate temporary cluster buffer");
> -        ret = -ENOMEM;
> -        goto fail;
> -    }
> -
>      s->cluster_cache_offset = -1;
>      s->flags = flags;
>  
> @@ -1507,8 +1497,6 @@ static int qcow2_do_open(BlockDriverState *bs, QDict *options, int flags,
>      if (s->refcount_block_cache) {
>          qcow2_cache_destroy(bs, s->refcount_block_cache);
>      }
> -    g_free(s->cluster_cache);
> -    qemu_vfree(s->cluster_data);
>      qcrypto_block_free(s->crypto);
>      qapi_free_QCryptoBlockOpenOptions(s->crypto_opts);
>      return ret;
>
Stefan Hajnoczi Aug. 21, 2017, 1:50 p.m. UTC | #3
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 <aik@ozlabs.ru>
> > Cc: Kevin Wolf <kwolf@redhat.com>
> > Signed-off-by: Stefan Hajnoczi <stefanha@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
diff mbox

Patch

diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c
index f06c08f64c..c47600a44e 100644
--- a/block/qcow2-cluster.c
+++ 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;
+            }
+        }
+        if (!s->cluster_cache) {
+            s->cluster_cache = g_malloc(s->cluster_size);
+        }
+
         BLKDBG_EVENT(bs->file, BLKDBG_READ_COMPRESSED);
         ret = bdrv_read(bs->file, coffset >> 9, s->cluster_data,
                         nb_csectors);
diff --git a/block/qcow2.c b/block/qcow2.c
index 40ba26c111..0ac201910a 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -1360,16 +1360,6 @@  static int qcow2_do_open(BlockDriverState *bs, QDict *options, int flags,
         goto fail;
     }
 
-    s->cluster_cache = g_malloc(s->cluster_size);
-    /* 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 == NULL) {
-        error_setg(errp, "Could not allocate temporary cluster buffer");
-        ret = -ENOMEM;
-        goto fail;
-    }
-
     s->cluster_cache_offset = -1;
     s->flags = flags;
 
@@ -1507,8 +1497,6 @@  static int qcow2_do_open(BlockDriverState *bs, QDict *options, int flags,
     if (s->refcount_block_cache) {
         qcow2_cache_destroy(bs, s->refcount_block_cache);
     }
-    g_free(s->cluster_cache);
-    qemu_vfree(s->cluster_data);
     qcrypto_block_free(s->crypto);
     qapi_free_QCryptoBlockOpenOptions(s->crypto_opts);
     return ret;