[PATCH 14/17] md: raid10: avoid direct access to bvec table in sync_request_write()

[Ming Lei]

The cost is 256bytes(8*16*2) stack space, and just use the bio
helper to retrieve pages from bio.

Signed-off-by: Ming Lei <tom.leim...@gmail.com>
---
 drivers/md/raid10.c | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
index 5c698f3d3083..69fe2a3cef89 100644
--- a/drivers/md/raid10.c
+++ b/drivers/md/raid10.c
@@ -2036,6 +2036,8 @@ static void sync_request_write(struct mddev *mddev, 
struct r10bio *r10_bio)
        int i, first;
        struct bio *tbio, *fbio;
        int vcnt;
+       struct bio_vec *bvl;
+       struct page *fbio_pages[RESYNC_PAGES], *tbio_pages[RESYNC_PAGES];
 
        atomic_set(&r10_bio->remaining, 1);
 
@@ -2052,6 +2054,10 @@ static void sync_request_write(struct mddev *mddev, 
struct r10bio *r10_bio)
        fbio->bi_iter.bi_size = r10_bio->sectors << 9;
        fbio->bi_iter.bi_idx = 0;
 
+       /* the bio has been filled up in raid10_sync_request */
+       bio_for_each_segment_all(bvl, fbio, i)
+               fbio_pages[i] = bvl->bv_page;
+
        vcnt = (r10_bio->sectors + (PAGE_SIZE >> 9) - 1) >> (PAGE_SHIFT - 9);
        /* now find blocks with errors */
        for (i=0 ; i < conf->copies ; i++) {
@@ -2072,12 +2078,17 @@ static void sync_request_write(struct mddev *mddev, 
struct r10bio *r10_bio)
                         * All vec entries are PAGE_SIZE;
                         */
                        int sectors = r10_bio->sectors;
+
+                       /* the bio has been filled up in raid10_sync_request */
+                       bio_for_each_segment_all(bvl, tbio, j)
+                               tbio_pages[j] = bvl->bv_page;
+
                        for (j = 0; j < vcnt; j++) {
                                int len = PAGE_SIZE;
                                if (sectors < (len / 512))
                                        len = sectors * 512;
-                               if 
(memcmp(page_address(fbio->bi_io_vec[j].bv_page),
-                                          
page_address(tbio->bi_io_vec[j].bv_page),
+                               if (memcmp(page_address(fbio_pages[j]),
+                                          page_address(tbio_pages[j]),
                                           len))
                                        break;
                                sectors -= len/512;
-- 
2.7.4