[sheepdog] [PATCH] cache: correct block size calculation for inode object

[Liu Yuan]

On Thu, Aug 08, 2013 at 06:51:22AM +0900, MORITA Kazutaka wrote:
> At Wed,  7 Aug 2013 16:10:01 +0800,
> Liu Yuan wrote:
> > 
> > inode and data object have different sizes and thus cache block size is
> > different. Current code fail to get the right size for inode object when
> > its last bit of bmap is set with the fixed block size.
> > 
> > This patch tries to get the dynamic block size based on the oid.
> > 
> > Signed-off-by: Liu Yuan <namei.unix at gmail.com>
> > ---
> >  sheep/object_cache.c |   36 ++++++++++++++++--------------------
> >  1 file changed, 16 insertions(+), 20 deletions(-)
> > 
> > diff --git a/sheep/object_cache.c b/sheep/object_cache.c
> > index dcf6972..957b052 100644
> > --- a/sheep/object_cache.c
> > +++ b/sheep/object_cache.c
> > @@ -28,8 +28,6 @@
> >  
> >  #define CACHE_INDEX_MASK      (CACHE_CREATE_BIT)
> >  
> > -#define CACHE_BLOCK_SIZE      ((UINT64_C(1) << 10) * 64) /* 64 KB */
> > -
> >  #define CACHE_OBJECT_SIZE (SD_DATA_OBJ_SIZE / 1024 / 1024) /* M */
> >  
> >  /* Kick background pusher if dirty_count greater than it */
> > @@ -116,13 +114,19 @@ static inline bool idx_has_vdi_bit(uint32_t idx)
> >  	return !!(idx & CACHE_VDI_BIT);
> >  }
> >  
> > -static uint64_t calc_object_bmap(size_t len, off_t offset)
> > +static inline int get_cache_block_size(uint64_t oid)
> > +{
> > +	return DIV_ROUND_UP(get_objsize(oid), sizeof(uint64_t) * BITS_PER_BYTE);
> > +}
> 
> The size of cache block must be sector-aligned for O_DIRECT.  I'd
> suggest rounding up to 4 KB boundary (the size of blocks for most
> filesystems) like as follows.
> 
>   static inline int get_cache_block_size(uint64_t oid)
>   {
>       int bsize = DIV_ROUND_UP(get_objsize(oid), sizeof(uint64_t) * BITS_PER_BYTE);
> 
>       return round_up(bsize, BLOCK_SIZE);
>   }

data object is aiglied, and inode object isn't. But this is problem since we
always drop O_DIRECT for inode object, no?

If we round up size for inode object, we need much more code to handle last
block of inode object.

Thanks
Yuan