[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH] drivers/block/xen-blkback/common.h: use DIV_ROUND_UP instead of reimplementing its function
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 _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxxx https://lists.xenproject.org/mailman/listinfo/xen-devel
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