On Mon, Sep 24, 2018 at 02:28:26PM +0100, Julien Grall wrote: > Hi Roger, > > On 09/12/2018 11:29 AM, Roger Pau Monné wrote: > > On Wed, Sep 12, 2018 at 10:48:42AM +0100, Julien Grall wrote: > > > 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. > > > > I don't think I agree with this last part, SEGS_PER_INDIRECT_FRAME > > would have to take into account XEN_PAGES_PER_SEGMENT, and > > XEN_PAGES_PER_INDIRECT_FRAME doesn't. > > > > XEN_PAGES_PER_INDIRECT_FRAME currently returns the number of grant > > references per indirect page, but as I understand it a segment can use > > more than one grant reference, if for example the guest page size is > > 64KB. > > I am a bit confused. By segment, do you refer to the backend or frontend > segment? Backend segment. I guess it's quite messy to have both frontend segment size and backend segment size which can be different. > In any case, it would be possible to remove SEGS_PER_INDIRECT_FRAME if we > rework MAX_INDIRECT_PAGES(...). This should improve the readability as well. Yes, I think this should improve the code. Roger.
