From: Bobi Jam <bobijam...@intel.com>

When a read ahead does not reach the end of the region reserved from
ras, we'd set ras::ras_next_readahead back to where we left off; For
stride read ahead, it needs to make sure that the offset is no less
than ras_stride_offset, so that the stride read ahead can work
correctly.

Signed-off-by: Bobi Jam <bobijam...@intel.com>
Intel-bug-id: https://jira.hpdd.intel.com/browse/LU-5263
Reviewed-on: http://review.whamcloud.com/11181
Reviewed-by: Fan Yong <fan.y...@intel.com>
Reviewed-by: wang di <di.w...@intel.com>
Reviewed-by: Oleg Drokin <oleg.dro...@intel.com>
Signed-off-by: James Simmons <jsimm...@infradead.org>
---
 drivers/staging/lustre/lustre/llite/rw.c |   18 +++++++++++++++---
 1 files changed, 15 insertions(+), 3 deletions(-)

diff --git a/drivers/staging/lustre/lustre/llite/rw.c 
b/drivers/staging/lustre/lustre/llite/rw.c
index 25de3bf..de20b7d 100644
--- a/drivers/staging/lustre/lustre/llite/rw.c
+++ b/drivers/staging/lustre/lustre/llite/rw.c
@@ -413,7 +413,7 @@ static int ll_read_ahead_pages(const struct lu_env *env,
                         * forward read-ahead, it will be fixed when backward
                         * read-ahead is implemented
                         */
-                       LASSERTF(page_idx > ria->ria_stoff, "Invalid page_idx 
%lu rs %lu re %lu ro %lu rl %lu rp %lu\n",
+                       LASSERTF(page_idx >= ria->ria_stoff, "Invalid page_idx 
%lu rs %lu re %lu ro %lu rl %lu rp %lu\n",
                                 page_idx,
                                 ria->ria_start, ria->ria_end, ria->ria_stoff,
                                 ria->ria_length, ria->ria_pages);
@@ -474,10 +474,22 @@ int ll_readahead(const struct lu_env *env, struct cl_io 
*io,
        }
 
        /* Reserve a part of the read-ahead window that we'll be issuing */
-       if (ras->ras_window_len) {
-               start = ras->ras_next_readahead;
+       if (ras->ras_window_len > 0) {
+               /*
+                * Note: other thread might rollback the ras_next_readahead,
+                * if it can not get the full size of prepared pages, see the
+                * end of this function. For stride read ahead, it needs to
+                * make sure the offset is no less than ras_stride_offset,
+                * so that stride read ahead can work correctly.
+                */
+               if (stride_io_mode(ras))
+                       start = max(ras->ras_next_readahead,
+                                   ras->ras_stride_offset);
+               else
+                       start = ras->ras_next_readahead;
                end = ras->ras_window_start + ras->ras_window_len - 1;
        }
+
        if (end != 0) {
                unsigned long rpc_boundary;
                /*
-- 
1.7.1

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