Re: [Qemu-devel] [PATCH for 2.6 1/3] backup: Use Bitmap to replace "s->bitmap"

[Fam Zheng]

On Mon, 11/23 17:01, Wen Congyang wrote:
> On 11/20/2015 05:59 PM, Fam Zheng wrote:
> > "s->bitmap" tracks done sectors, we only check bit states without using any
> > iterator which HBitmap is good for. Switch to "Bitmap" which is simpler and
> > more memory efficient.
> > 
> > Meanwhile, rename it to done_bitmap, to reflect the intention.
> > 
> > Signed-off-by: Fam Zheng <address@hidden>
> > ---
> >  block/backup.c | 11 ++++++-----
> >  1 file changed, 6 insertions(+), 5 deletions(-)
> > 
> > diff --git a/block/backup.c b/block/backup.c
> > index 3b39119..d408f98 100644
> > --- a/block/backup.c
> > +++ b/block/backup.c
> > @@ -22,6 +22,7 @@
> >  #include "qapi/qmp/qerror.h"
> >  #include "qemu/ratelimit.h"
> >  #include "sysemu/block-backend.h"
> > +#include "qemu/bitmap.h"
> >  
> >  #define BACKUP_CLUSTER_BITS 16
> >  #define BACKUP_CLUSTER_SIZE (1 << BACKUP_CLUSTER_BITS)
> > @@ -47,7 +48,7 @@ typedef struct BackupBlockJob {
> >      BlockdevOnError on_target_error;
> >      CoRwlock flush_rwlock;
> >      uint64_t sectors_read;
> > -    HBitmap *bitmap;
> > +    unsigned long *done_bitmap;
> >      QLIST_HEAD(, CowRequest) inflight_reqs;
> >  } BackupBlockJob;
> >  
> > @@ -113,7 +114,7 @@ static int coroutine_fn backup_do_cow(BlockDriverState 
> > *bs,
> >      cow_request_begin(&cow_request, job, start, end);
> >  
> >      for (; start < end; start++) {
> > -        if (hbitmap_get(job->bitmap, start)) {
> > +        if (test_bit(start, job->done_bitmap)) {
> >              trace_backup_do_cow_skip(job, start);
> >              continue; /* already copied */
> >          }
> > @@ -164,7 +165,7 @@ static int coroutine_fn backup_do_cow(BlockDriverState 
> > *bs,
> >              goto out;
> >          }
> >  
> > -        hbitmap_set(job->bitmap, start, 1);
> > +        bitmap_set(job->done_bitmap, start, 1);
> 
> You can use set_bit() here.

Why? I think bitmap_set is a better match with bitmap_new below.

Fam

> 
> Thanks
> Wen Congyang
> 
> >  
> >          /* Publish progress, guest I/O counts as progress too.  Note that 
> > the
> >           * offset field is an opaque progress value, it is not a disk 
> > offset.
> > @@ -394,7 +395,7 @@ static void coroutine_fn backup_run(void *opaque)
> >      start = 0;
> >      end = DIV_ROUND_UP(job->common.len, BACKUP_CLUSTER_SIZE);
> >  
> > -    job->bitmap = hbitmap_alloc(end, 0);
> > +    job->done_bitmap = bitmap_new(end);
> >  
> >      bdrv_set_enable_write_cache(target, true);
> >      if (target->blk) {
> > @@ -475,7 +476,7 @@ static void coroutine_fn backup_run(void *opaque)
> >      /* wait until pending backup_do_cow() calls have completed */
> >      qemu_co_rwlock_wrlock(&job->flush_rwlock);
> >      qemu_co_rwlock_unlock(&job->flush_rwlock);
> > -    hbitmap_free(job->bitmap);
> > +    g_free(job->done_bitmap);
> >  
> >      if (target->blk) {
> >          blk_iostatus_disable(target->blk);
> > 
>