Re: Re: question about striped_read

[majianpeng <majianpeng@gmail.com>]

 [snip]
Test case
A: touch file
    dd if=file of=/dev/null bs=5M count=1 iflag=direct
B: [data(2M)|hole(2m)][data(2M)]
   dd if=file of=/dev/null bs=8M count=1 iflag=direct
C: [data(4M)[hole(4M)][hole(4M)][data(2M)]
  dd if=file of=/dev/null bs=16M count=1 iflag=direct
D: touch file;truncate -s 5M file
  dd if=file of=/dev/null bs=8M count=1 iflag=direct

Those cases can work.
Now i make different processing  for short-read between 'ret > 0' and "ret =0".
For the short-read which ret > 0, it don't do read-page rather than zero the left area.
This means reduce one meaningless read operation.

diff --git a/fs/ceph/file.c b/fs/ceph/file.c
index 2ddf061..f643ec8 100644
--- a/fs/ceph/file.c
+++ b/fs/ceph/file.c
@@ -350,13 +350,17 @@ more:
             ret, hit_stripe ? " HITSTRIPE" : "", was_short ? " SHORT" : "");
 
        if (ret > 0) {
-               int didpages = (page_align + ret) >> PAGE_CACHE_SHIFT;
-
-               if (read < pos - off) {
diff --git a/fs/ceph/file.c b/fs/ceph/file.c
index 2ddf061..f643ec8 100644
--- a/fs/ceph/file.c
+++ b/fs/ceph/file.c
@@ -350,13 +350,17 @@ more:
             ret, hit_stripe ? " HITSTRIPE" : "", was_short ? " SHORT" : "");
 
        if (ret > 0) {
-               int didpages = (page_align + ret) >> PAGE_CACHE_SHIFT;
-
-               if (read < pos - off) {
-                       dout(" zero gap %llu to %llu\n", off + read, pos);
-                       ceph_zero_page_vector_range(page_align + read,
-                                                   pos - off - read, pages);
+               int  didpages;
+
+               if (was_short && pos + ret < inode->i_size) {
+                        u64 tmp = min(this_len - ret, 
+                                        	inode->i_size - pos - ret);
+                        dout(" zero gap %llu to %llu\n", pos + ret, pos + ret + tmp);
+                        ceph_zero_page_vector_range(page_align + read + ret,
+                                                       tmp, pages);
+                        ret += tmp;
                }
+               didpages = (page_align + ret) >> PAGE_CACHE_SHIFT;
                pos += ret;
                read = pos - off;
                left -= ret;
@@ -375,13 +379,25 @@ more:
 
                /* zero trailing bytes (inside i_size) */
                if (left > 0 && pos < inode->i_size) {
+                       int didpages;
                        if (pos + left > inode->i_size)
                                left = inode->i_size - pos;
 
-                       dout("zero tail %d\n", left);
-                       ceph_zero_page_vector_range(page_align + read, left,
+                       ret = min(left, this_len);
+                       dout("zero tail %d\n", ret);
+                       ceph_zero_page_vector_range(page_align + read, ret,
                                                    pages);
-                       read += left;
+                       didpages = (page_align + ret) >> PAGE_CACHE_SHIFT;
+
+                       pos += ret;
+                       read = pos - off;
+                       left -= ret;
+                       page_pos += didpages;
+                       pages_left -= didpages;
+
+                       /* hit stripe? */
+                       if (left && hit_stripe)
+                               goto more;
                }
        }