Cleanup #4166
closedceph: simplify ceph_sync_write() page_align
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Description
(This work is done.)
ceph: simplify ceph_sync_write() page_align calculation
In ceph_sync_write() there is some magic that computes page_align
for an osd request. But a little analysis shows it can be
simplified.
First, we have:
io_align = pos & ~PAGE_MASK;
which is used here:
page_align = (pos - io_align + buf_align) & ~PAGE_MASK;
Note (pos - io_align) simply rounds "pos" down to the nearest multiple
of the page size.
We also have:
buf_align = (unsigned long)data & ~PAGE_MASK;
Adding buf_align to that rounded-down "pos" value will stay within
the same page; the result will just be offset by the page offset for
the "data" pointer. The final mask therefore leaves just the value
of "buf_align".
The same simplification can be done in striped_read().
One more simplification. Note that the result of calc_pages_for()
is invariant of which page the offset starts in--the only thing that
matters is the offset within the starting page. We will have
put the proper page offset to use into "page_align", so just use
that in calculating num_pages.
Signed-off-by: Alex Elder <elder@inktank.com>