LU-12043 llite: don't miss every first stride page

Whenever we need skip some pages for stride io read, we
will calculate next start page index, however, this page
index is skipped every time, because loop start from index + 1

Testing command: iozone -w -c -i 5 -t1 -j 2 -s 100m -r 1m -F data
Without patch: 587384.69 kB/sec

                        read                    write
pages per rpc         rpcs   % cum % |       rpcs   % cum %
1:                      16  19  19   |          0   0   0
2:                       0   0  19   |          0   0   0
4:                       0   0  19   |          0   0   0
8:                       0   0  19   |          0   0   0
16:                      0   0  19   |          0   0   0
32:                      0   0  19   |          0   0   0
64:                      0   0  19   |          0   0   0
128:                     0   0  19   |          0   0   0
256:                     0   0  19   |          0   0   0
512:                    22  26  46   |          0   0   0
1024:                   44  53 100   |          0   0   0

With patch: 744635.56 kB/sec
                        read                    write
pages per rpc         rpcs   % cum % |       rpcs   % cum %
1:                       0   0   0   |          0   0   0
2:                       0   0   0   |          0   0   0
4:                       0   0   0   |          0   0   0
8:                       0   0   0   |          0   0   0
16:                      0   0   0   |          0   0   0
32:                      0   0   0   |          0   0   0
64:                      0   0   0   |          0   0   0
128:                     0   0   0   |          0   0   0
256:                     0   0   0   |          0   0   0
512:                     8  13  13   |          0   0   0
1024:                   50  86 100   |          0   0   0

We get better performances ~27% up here, and all 1 page RPC
disappear.

Change-Id: I126674cbe15197f0abdff256fdde3fc0c49c6898
Signed-off-by: Wang Shilong <wshilong@ddn.com>
Reviewed-on: https://review.whamcloud.com/35216
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: Li Xi <lixi@ddn.com>
Reviewed-by: Patrick Farrell <pfarrell@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>

diff --git a/lustre/llite/rw.c b/lustre/llite/rw.c
index 27442a4..cda05f6 100644 (file)
--- a/lustre/llite/rw.c
+++ b/lustre/llite/rw.c
@@ -398,14 +398,16 @@ ll_read_ahead_pages(const struct lu_env *env, struct cl_io *io,
                                ria->ria_reserved--;
                                count++;
                        }
-                } else if (stride_ria) {
-                        /* If it is not in the read-ahead window, and it is
-                         * read-ahead mode, then check whether it should skip
-                         * the stride gap */
-                        pgoff_t offset;
-                        /* FIXME: This assertion only is valid when it is for
-                         * forward read-ahead, it will be fixed when backward
-                         * read-ahead is implemented */
+               } else if (stride_ria) {
+                       /* If it is not in the read-ahead window, and it is
+                        * read-ahead mode, then check whether it should skip
+                        * the stride gap.
+                        */
+                       pgoff_t offset;
+                       /* NOTE: This assertion only is valid when it is for
+                        * forward read-ahead, must adjust if backward
+                        * readahead is implemented.
+                        */
                        LASSERTF(page_idx >= ria->ria_stoff,
                                "Invalid page_idx %lu rs %lu re %lu ro %lu "
                                "rl %lu rp %lu\n", page_idx,
@@ -413,14 +415,15 @@ ll_read_ahead_pages(const struct lu_env *env, struct cl_io *io,
                                ria->ria_length, ria->ria_pages);
                         offset = page_idx - ria->ria_stoff;
                         offset = offset % (ria->ria_length);
-                        if (offset > ria->ria_pages) {
-                                page_idx += ria->ria_length - offset;
-                                CDEBUG(D_READA, "i %lu skip %lu \n", page_idx,
-                                       ria->ria_length - offset);
-                                continue;
-                        }
-                }
-        }
+                       if (offset >= ria->ria_pages) {
+                               page_idx += ria->ria_length - offset - 1;
+                               CDEBUG(D_READA,
+                                      "Stride: jump %lu pages to %lu\n",
+                                      ria->ria_length - offset, page_idx);
+                               continue;
+                       }
+               }
+       }
 
        cl_read_ahead_release(env, &ra);