[lustre-devel] [PATCH 06/13] lustre: readahead: fix reserving for unaliged read

[James Simmons]

From: Wang Shilong <wshilong at ddn.com>

If read is [2K, 3K] on x86 platform, we only need
read one page, but it was calculated as 2 pages.

This could be problem, as we need reserve more
pages credits, vvp_page_completion_read() will only
free actual reading pages, which cause @ra_cur_pages
leaked.

Fixes: cc603a90cca ("lustre: llite: Fix page count for unaligned reads")
WC-bug-id: https://jira.whamcloud.com/browse/LU-14616
Lustre-commit: 5e7e9240d27a4b74 ("LU-14616 readahead: fix reserving for unaliged read")
Signed-off-by: Wang Shilong <wshilong at ddn.com>
Reviewed-on: https://review.whamcloud.com/43377
Reviewed-by: Andreas Dilger <adilger at whamcloud.com>
Reviewed-by: Bobi Jam <bobijam at hotmail.com>
Reviewed-by: Oleg Drokin <green at whamcloud.com>
Signed-off-by: James Simmons <jsimmons at infradead.org>
---
 fs/lustre/llite/rw.c     |  7 +++++++
 fs/lustre/llite/vvp_io.c | 18 ++++++++++++------
 2 files changed, 19 insertions(+), 6 deletions(-)

diff --git a/fs/lustre/llite/rw.c b/fs/lustre/llite/rw.c
index 8dcbef3..184e5e8 100644
--- a/fs/lustre/llite/rw.c
+++ b/fs/lustre/llite/rw.c
@@ -90,6 +90,13 @@ static unsigned long ll_ra_count_get(struct ll_sb_info *sbi,
 	 * LRU pages, otherwise, it could cause deadlock.
 	 */
 	pages = min(sbi->ll_cache->ccc_lru_max >> 2, pages);
+	/**
+	 * if this happen, we reserve more pages than needed,
+	 * this will make us leak @ra_cur_pages, because
+	 * ll_ra_count_put() acutally freed @pages.
+	 */
+	if (WARN_ON_ONCE(pages_min > pages))
+		pages_min = pages;
 
 	/*
 	 * If read-ahead pages left are less than 1M, do not do read-ahead,
diff --git a/fs/lustre/llite/vvp_io.c b/fs/lustre/llite/vvp_io.c
index e98792b..12a28d9 100644
--- a/fs/lustre/llite/vvp_io.c
+++ b/fs/lustre/llite/vvp_io.c
@@ -798,6 +798,7 @@ static int vvp_io_read_start(const struct lu_env *env,
 	int exceed = 0;
 	int result;
 	struct iov_iter iter;
+	pgoff_t page_offset;
 
 	CLOBINVRNT(env, obj, vvp_object_invariant(obj));
 
@@ -839,15 +840,20 @@ static int vvp_io_read_start(const struct lu_env *env,
 	if (!vio->vui_ra_valid) {
 		vio->vui_ra_valid = true;
 		vio->vui_ra_start_idx = cl_index(obj, pos);
-		vio->vui_ra_pages = cl_index(obj, tot + PAGE_SIZE - 1);
-		/* If both start and end are unaligned, we read one more page
-		 * than the index math suggests.
-		 */
-		if ((pos & ~PAGE_MASK) != 0 && ((pos + tot) & ~PAGE_MASK) != 0)
+		vio->vui_ra_pages = 0;
+		page_offset = pos & ~PAGE_MASK;
+		if (page_offset) {
 			vio->vui_ra_pages++;
+			if (tot > PAGE_SIZE - page_offset)
+				tot -= (PAGE_SIZE - page_offset);
+			else
+				tot = 0;
+		}
+		vio->vui_ra_pages += (tot + PAGE_SIZE - 1) >> PAGE_SHIFT;
 
 		CDEBUG(D_READA, "tot %zu, ra_start %lu, ra_count %lu\n",
-		       tot, vio->vui_ra_start_idx, vio->vui_ra_pages);
+		       vio->vui_tot_count, vio->vui_ra_start_idx,
+		       vio->vui_ra_pages);
 	}
 
 	/* BUG: 5972 */
-- 
1.8.3.1