On Fri, 30 Oct 2009, Noah Watkins wrote:
>
> > Actually, it looks like that calculation is wrong.. I also added
> >
> > *oxoff += (stripeno % su_per_object) * su;
>
> Looks like this update fixes the object offset for multiple stripes
> per object, but 'oxlen' needs adjusted. With the current calculation:
>
> - oxlen = min(plen, offset % su)
>
> A length of zero is calculated when offset equals stripe unit.
> Consider osize=128, stripe unit = 64, stripe count = 2. A write
> request of
>
> length, offset
> 4096, 0
>
> gives:
> ono = 0, oxoff = 0, oxlen = 64
> ono = 1, oxoff = 0, oxlen = 64
> ono = 0, oxoff = 64, oxlen = 0 <-- infinite loop wrt to calling context
>
> So, assuming that object size is a multiple of stripe unit, we really
> want the minimum between the total request and the remaining space in
> the current stripe:
>
> - oxlen = min(plen, su - (offset % su))
>
> I put a path in against ceph-client/unstable @
>
> http://code.noahdesu.com/git/linux26-dev.git ceph/unstable-for-sage
Applied, thanks!
sage
>
> -n
>
> -------------
>
> diff --git a/fs/ceph/osdmap.c b/fs/ceph/osdmap.c
> index 5a5520c..d62e111 100644
> --- a/fs/ceph/osdmap.c
> +++ b/fs/ceph/osdmap.c
> @@ -731,7 +731,7 @@ void ceph_calc_file_object_mapping(struct
> ceph_file_layout *layout,
> u32 sc = le32_to_cpu(layout->fl_stripe_count);
> u32 bl, stripeno, stripepos, objsetno;
> u32 su_per_object;
> - u64 t;
> + u64 t, su_offset;
>
> dout("mapping %llu~%llu osize %u fl_su %u\n", off, *plen,
> osize, su);
> @@ -755,10 +755,15 @@ void ceph_calc_file_object_mapping(struct
> ceph_file_layout *layout,
>
> /* *oxoff = *off % layout->fl_stripe_unit; # offset in su */
> t = off;
> - *oxoff = do_div(t, su);
> - *oxoff += (stripeno % su_per_object) * su;
> -
> - *oxlen = min_t(u64, *plen, su - *oxoff);
> + su_offset = do_div(t, su);
> + *oxoff = su_offset + (stripeno % su_per_object) * su;
> +
> + /*
> + * Calculate the length of the extent being written to the
> selected
> + * object. This is the minimum of the full length requested
> (plen) or
> + * the remainder of the current stripe being written to.
> + */
> + *oxlen = min_t(u64, *plen, su - su_offset);
> *plen = *oxlen;
>
> dout(" obj extent %llu~%llu\n", *oxoff, *oxlen);
>
>
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