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.
This resolves:
http://tracker.ceph.com/issues/4166
Signed-off-by: Alex Elder <elder@xxxxxxxxxxx>
---
fs/ceph/file.c | 18 +++++-------------
1 file changed, 5 insertions(+), 13 deletions(-)
diff --git a/fs/ceph/file.c b/fs/ceph/file.c
index 9c4325e..6123ad4 100644
--- a/fs/ceph/file.c
+++ b/fs/ceph/file.c
@@ -331,10 +331,7 @@ static int striped_read(struct inode *inode,
io_align = off & ~PAGE_MASK;
more:
- if (o_direct)
- page_align = (pos - io_align + buf_align) & ~PAGE_MASK;
- else
- page_align = pos & ~PAGE_MASK;
+ page_align = o_direct ? buf_align : io_align;
this_len = left;
ret = ceph_osdc_readpages(&fsc->client->osdc, ceph_vino(inode),
&ci->i_layout, pos, &this_len,
@@ -526,15 +523,10 @@ more:
io_align = pos & ~PAGE_MASK;
buf_align = (unsigned long)data & ~PAGE_MASK;
len = left;
- if (file->f_flags & O_DIRECT) {
- /* write from beginning of first page, regardless of
- io alignment */
- page_align = (pos - io_align + buf_align) & ~PAGE_MASK;
- num_pages = calc_pages_for((unsigned long)data, len);
- } else {
- page_align = pos & ~PAGE_MASK;
- num_pages = calc_pages_for(pos, len);
- }
+
+ /* write from beginning of first page, regardless of io alignment */
+ page_align = file->f_flags & O_DIRECT ? buf_align : io_align;
+ num_pages = calc_pages_for(page_align, len);
req = ceph_osdc_new_request(&fsc->client->osdc, &ci->i_layout,
ceph_vino(inode), pos, &len,
CEPH_OSD_OP_WRITE, flags,
--
1.7.9.5
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