raid5-cache: statically allocate the recovery ra bio

There is no need to preallocate the bio and reset it when use.  Just
allocate it on-stack and use a bvec places next to the pages used for
it.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Song Liu <song@kernel.org>

drivers/md/raid5-cache.c

@@ -1623,22 +1623,17 @@ struct r5l_recovery_ctx {
 	 * just copy data from the pool.
 	 */
 	struct page *ra_pool[R5L_RECOVERY_PAGE_POOL_SIZE];
+	struct bio_vec ra_bvec[R5L_RECOVERY_PAGE_POOL_SIZE];
 	sector_t pool_offset;	/* offset of first page in the pool */
 	int total_pages;	/* total allocated pages */
 	int valid_pages;	/* pages with valid data */
-	struct bio *ra_bio;	/* bio to do the read ahead */
 };
 
 static int r5l_recovery_allocate_ra_pool(struct r5l_log *log,
 					    struct r5l_recovery_ctx *ctx)
 {
 	struct page *page;
 
-	ctx->ra_bio = bio_alloc_bioset(NULL, BIO_MAX_VECS, 0, GFP_KERNEL,
-				       &log->bs);
-	if (!ctx->ra_bio)
-		return -ENOMEM;
-
 	ctx->valid_pages = 0;
 	ctx->total_pages = 0;
 	while (ctx->total_pages < R5L_RECOVERY_PAGE_POOL_SIZE) {
@@ -1650,10 +1645,8 @@ static int r5l_recovery_allocate_ra_pool(struct r5l_log *log,
 		ctx->total_pages += 1;
 	}
 
-	if (ctx->total_pages == 0) {
-		bio_put(ctx->ra_bio);
+	if (ctx->total_pages == 0)
 		return -ENOMEM;
-	}
 
 	ctx->pool_offset = 0;
 	return 0;
@@ -1666,7 +1659,6 @@ static void r5l_recovery_free_ra_pool(struct r5l_log *log,
 
 	for (i = 0; i < ctx->total_pages; ++i)
 		put_page(ctx->ra_pool[i]);
-	bio_put(ctx->ra_bio);
 }
 
 /*
@@ -1679,15 +1671,19 @@ static int r5l_recovery_fetch_ra_pool(struct r5l_log *log,
 				      struct r5l_recovery_ctx *ctx,
 				      sector_t offset)
 {
-	bio_reset(ctx->ra_bio, log->rdev->bdev, REQ_OP_READ);
-	ctx->ra_bio->bi_iter.bi_sector = log->rdev->data_offset + offset;
+	struct bio bio;
+	int ret;
+
+	bio_init(&bio, log->rdev->bdev, ctx->ra_bvec,
+		 R5L_RECOVERY_PAGE_POOL_SIZE, REQ_OP_READ);
+	bio.bi_iter.bi_sector = log->rdev->data_offset + offset;
 
 	ctx->valid_pages = 0;
 	ctx->pool_offset = offset;
 
 	while (ctx->valid_pages < ctx->total_pages) {
-		bio_add_page(ctx->ra_bio,
-			     ctx->ra_pool[ctx->valid_pages], PAGE_SIZE, 0);
+		__bio_add_page(&bio, ctx->ra_pool[ctx->valid_pages], PAGE_SIZE,
+			       0);
 		ctx->valid_pages += 1;
 
 		offset = r5l_ring_add(log, offset, BLOCK_SECTORS);
@@ -1696,7 +1692,9 @@ static int r5l_recovery_fetch_ra_pool(struct r5l_log *log,
 			break;
 	}
 
-	return submit_bio_wait(ctx->ra_bio);
+	ret = submit_bio_wait(&bio);
+	bio_uninit(&bio);
+	return ret;
 }
 
 /*