Messages in this thread | | | Date | Thu, 14 Feb 2008 20:18:02 +0200 | From | "Pekka Enberg" <> | Subject | Re: [PATCH 2/6] fs/direct-io.c: Use DIV_ROUND_UP |
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Hi Nishanth,
On Thu, Feb 14, 2008 at 7:38 PM, Nishanth Aravamudan <nacc@us.ibm.com> wrote: > Is it just me, or does > > ((user_addr + iov[seg].iov_len + PAGE_SIZE - 1)/PAGE_SIZE - user_addr/PAGE_SIZE) > > not simplify to > > = ((iov[seg].iov_len + PAGE_SIZE - 1)/PAGE_SIZE + user_addr/PAGE_SIZE - user_addr/PAGE_SIZE) > > = ((iov[seg].iov_len + PAGE_SIZE - 1)/PAGE_SIZE) > > = DIV_ROUND_UP(iov[seg].iov_len, PAGE_SIZE) > > CMIIW.
I double-checked this and I believe you're correct. It's simpler to see when you do:
x = user_addr y = iov[seg].iov_len z = PAGE_SIZE
So
(x + y + z - 1)/z - x/z
= [x + (y + z - 1)]/z - x/z
= [xz + z(y + z - 1)]/z^2 - x/z
= x/z + (y + z - 1)/z - x/z
And the rest follows from your simplifications.
Pekka
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