Hi,
On 09/12/2018 10:16 AM, Roger Pau Monné wrote:
On Wed, Sep 12, 2018 at 11:13:50AM +0200, Roger Pau Monné wrote:
Adding Julien how did the work to support XEN_PAGE_SIZE != PAGE_SIZE.
On Wed, Sep 12, 2018 at 02:14:26AM -0600, Jan Beulich wrote:
On 12.09.18 at 07:45, <zhongjiang@xxxxxxxxxx> wrote:
--- a/drivers/block/xen-blkback/common.h
+++ b/drivers/block/xen-blkback/common.h
@@ -65,7 +65,7 @@
(XEN_PAGES_PER_INDIRECT_FRAME / XEN_PAGES_PER_SEGMENT)
#define MAX_INDIRECT_PAGES \
- ((MAX_INDIRECT_SEGMENTS + SEGS_PER_INDIRECT_FRAME - 1)/SEGS_PER_INDIRECT_FRAME)
+ DIV_ROUND_UP(MAX_INDIRECT_SEGMENTS, SEGS_PER_INDIRECT_FRAME)
#define INDIRECT_PAGES(_segs) DIV_ROUND_UP(_segs, XEN_PAGES_PER_INDIRECT_FRAME)
My first reaction was to suggest
#define MAX_INDIRECT_PAGES INDIRECT_PAGES(MAX_INDIRECT_SEGMENTS)
but that wouldn't match what's there currently (note the two different
divisors). I can't really decide whether that's just unfortunate naming
of the two macros, or an actual bug.
I think there's indeed a bug here.
AFAICT, MAX_INDIRECT_PAGES should use XEN_PAGES_PER_INDIRECT_FRAME and
then it could be changed as Jan suggested.
The problem is SEGS_PER_INDIRECT_FRAME has been miscalculated. So I
think it would be fine to use XEN_PAGES_PER_INDIRECT_FRAME in
MAX_INDIRECT_PAGES.
However the naming for XEN_PAGES_PER_INDIRECT_FRAME is misnamed. We
return number of a for segments per indirect frame. So I would rename to
SEGS_PER_INDIRECT_FRAME.
Current MAX_INDIRECT_PAGES is misnamed and should instead be
MAX_INDIRECT_SEGS (which on x86 is exactly the same because PAGE_SIZE
== XEN_PAGE_SIZE).
Looking at the usage:
j = min(MAX_INDIRECT_PAGES, INDIRECT_PAGES(nr_segments))
Where j is used as the number of grant ref. So I don't think the
variable is misnamed here.
Cheers,
--
Julien Grall
