[PATCH] md/r5cache: improve recovery with read ahead page pool

[Song Liu <songliubraving@fb.com>]

In r5cache recovery, the journal device is scanned page by page.
Currently, we use sync_page_io() to read journal device. This is
not efficient when we have to recovery many stripes from the journal.

To improve the speed of recovery, this patch introduces a read ahead
page pool (ra_pool) to recovery_ctx. With ra_pool, multiple consecutive
pages are read in one IO. Then the recovery code read the journal from
ra_pool.

Signed-off-by: Song Liu <songliubraving@fb.com>
---
 drivers/md/raid5-cache.c | 151 +++++++++++++++++++++++++++++++++++++++++------
 1 file changed, 134 insertions(+), 17 deletions(-)

diff --git a/drivers/md/raid5-cache.c b/drivers/md/raid5-cache.c
index 3f307be..46afea8 100644
--- a/drivers/md/raid5-cache.c
+++ b/drivers/md/raid5-cache.c
@@ -1552,6 +1552,8 @@ bool r5l_log_disk_error(struct r5conf *conf)
 	return ret;
 }
 
+#define R5L_RECOVERY_PAGE_POOL_SIZE 64
+
 struct r5l_recovery_ctx {
 	struct page *meta_page;		/* current meta */
 	sector_t meta_total_blocks;	/* total size of current meta and data */
@@ -1560,18 +1562,130 @@ struct r5l_recovery_ctx {
 	int data_parity_stripes;	/* number of data_parity stripes */
 	int data_only_stripes;		/* number of data_only stripes */
 	struct list_head cached_list;
+
+	/*
+	 * read ahead page pool (ra_pool)
+	 * in recovery, log is read sequentially. It is not efficient to
+	 * read every page with sync_page_io(). The read ahead page pool
+	 * reads multiple pages with one IO, so further log read can
+	 * just copy data from the pool.
+	 */
+	struct page *ra_pool[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(GFP_KERNEL, BIO_MAX_PAGES, 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) {
+		page = alloc_page(GFP_KERNEL);
+
+		if (!page)
+			break;
+		ctx->ra_pool[ctx->total_pages] = page;
+		ctx->total_pages += 1;
+	}
+
+	if (ctx->total_pages == 0) {
+		bio_put(ctx->ra_bio);
+		return -ENOMEM;
+	}
+
+	ctx->pool_offset = 0;
+	return 0;
+}
+
+static void r5l_recovery_free_ra_pool(struct r5l_log *log,
+					struct r5l_recovery_ctx *ctx)
+{
+	int i;
+
+	for (i = 0; i < ctx->total_pages; ++i)
+		put_page(ctx->ra_pool[i]);
+	bio_put(ctx->ra_bio);
+}
+
+/*
+ * fetch ctx->valid_pages pages from offset
+ * In normal cases, ctx->valid_pages == ctx->total_pages after the call.
+ * However, if the offset is close to the end of the journal device,
+ * ctx->valid_pages could be smaller than ctx->total_pages
+ */
+static int r5l_recovery_fetch_ra_pool(struct r5l_log *log,
+				      struct r5l_recovery_ctx *ctx,
+				      sector_t offset)
+{
+	bio_reset(ctx->ra_bio);
+	ctx->ra_bio->bi_bdev = log->rdev->bdev;
+	bio_set_op_attrs(ctx->ra_bio, REQ_OP_READ, 0);
+	ctx->ra_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);
+		ctx->valid_pages += 1;
+
+		offset = r5l_ring_add(log, offset, BLOCK_SECTORS);
+
+		if (offset == 0)  /* reached end of the device */
+			break;
+	}
+
+	return submit_bio_wait(ctx->ra_bio);
+}
+
+/*
+ * try read a page from the read ahead page pool, if the page is not in the
+ * pool, call r5l_recovery_fetch_ra_pool
+ */
+static int r5l_recovery_read_page(struct r5l_log *log,
+				  struct r5l_recovery_ctx *ctx,
+				  struct page *page,
+				  sector_t offset)
+{
+	int ret;
+
+	if (offset < ctx->pool_offset ||
+	    offset >= ctx->pool_offset + ctx->valid_pages * BLOCK_SECTORS) {
+		ret = r5l_recovery_fetch_ra_pool(log, ctx, offset);
+		if (ret)
+			return ret;
+	}
+
+	BUG_ON(offset < ctx->pool_offset ||
+	       offset >= ctx->pool_offset + ctx->valid_pages * BLOCK_SECTORS);
+
+	memcpy(page_address(page),
+	       page_address(ctx->ra_pool[(offset - ctx->pool_offset) / BLOCK_SECTORS]),
+	       PAGE_SIZE);
+	return 0;
+}
+
 static int r5l_recovery_read_meta_block(struct r5l_log *log,
 					struct r5l_recovery_ctx *ctx)
 {
 	struct page *page = ctx->meta_page;
 	struct r5l_meta_block *mb;
 	u32 crc, stored_crc;
+	int ret;
 
-	if (!sync_page_io(log->rdev, ctx->pos, PAGE_SIZE, page, REQ_OP_READ, 0,
-			  false))
-		return -EIO;
+	ret = r5l_recovery_read_page(log, ctx, page, ctx->pos);
+	if (ret != 0)
+		return ret;
 
 	mb = page_address(page);
 	stored_crc = le32_to_cpu(mb->checksum);
@@ -1653,8 +1767,7 @@ static void r5l_recovery_load_data(struct r5l_log *log,
 	raid5_compute_sector(conf,
 			     le64_to_cpu(payload->location), 0,
 			     &dd_idx, sh);
-	sync_page_io(log->rdev, log_offset, PAGE_SIZE,
-		     sh->dev[dd_idx].page, REQ_OP_READ, 0, false);
+	r5l_recovery_read_page(log, ctx, sh->dev[dd_idx].page, log_offset);
 	sh->dev[dd_idx].log_checksum =
 		le32_to_cpu(payload->checksum[0]);
 	ctx->meta_total_blocks += BLOCK_SECTORS;
@@ -1673,17 +1786,13 @@ static void r5l_recovery_load_parity(struct r5l_log *log,
 	struct r5conf *conf = mddev->private;
 
 	ctx->meta_total_blocks += BLOCK_SECTORS * conf->max_degraded;
-	sync_page_io(log->rdev, log_offset, PAGE_SIZE,
-		     sh->dev[sh->pd_idx].page, REQ_OP_READ, 0, false);
+	r5l_recovery_read_page(log, ctx, sh->dev[sh->pd_idx].page, log_offset);
 	sh->dev[sh->pd_idx].log_checksum =
 		le32_to_cpu(payload->checksum[0]);
 	set_bit(R5_Wantwrite, &sh->dev[sh->pd_idx].flags);
 
 	if (sh->qd_idx >= 0) {
-		sync_page_io(log->rdev,
-			     r5l_ring_add(log, log_offset, BLOCK_SECTORS),
-			     PAGE_SIZE, sh->dev[sh->qd_idx].page,
-			     REQ_OP_READ, 0, false);
+		r5l_recovery_read_page(log, ctx, sh->dev[sh->qd_idx].page, log_offset);
 		sh->dev[sh->qd_idx].log_checksum =
 			le32_to_cpu(payload->checksum[1]);
 		set_bit(R5_Wantwrite, &sh->dev[sh->qd_idx].flags);
@@ -1814,14 +1923,15 @@ r5c_recovery_replay_stripes(struct list_head *cached_stripe_list,
 
 /* if matches return 0; otherwise return -EINVAL */
 static int
-r5l_recovery_verify_data_checksum(struct r5l_log *log, struct page *page,
+r5l_recovery_verify_data_checksum(struct r5l_log *log,
+				  struct r5l_recovery_ctx *ctx,
+				  struct page *page,
 				  sector_t log_offset, __le32 log_checksum)
 {
 	void *addr;
 	u32 checksum;
 
-	sync_page_io(log->rdev, log_offset, PAGE_SIZE,
-		     page, REQ_OP_READ, 0, false);
+	r5l_recovery_read_page(log, ctx, page, log_offset);
 	addr = kmap_atomic(page);
 	checksum = crc32c_le(log->uuid_checksum, addr, PAGE_SIZE);
 	kunmap_atomic(addr);
@@ -1853,17 +1963,17 @@ r5l_recovery_verify_data_checksum_for_mb(struct r5l_log *log,
 
 		if (payload->header.type == R5LOG_PAYLOAD_DATA) {
 			if (r5l_recovery_verify_data_checksum(
-				    log, page, log_offset,
+				    log, ctx, page, log_offset,
 				    payload->checksum[0]) < 0)
 				goto mismatch;
 		} else if (payload->header.type == R5LOG_PAYLOAD_PARITY) {
 			if (r5l_recovery_verify_data_checksum(
-				    log, page, log_offset,
+				    log, ctx, page, log_offset,
 				    payload->checksum[0]) < 0)
 				goto mismatch;
 			if (conf->max_degraded == 2 && /* q for RAID 6 */
 			    r5l_recovery_verify_data_checksum(
-				    log, page,
+				    log, ctx, page,
 				    r5l_ring_add(log, log_offset,
 						 BLOCK_SECTORS),
 				    payload->checksum[1]) < 0)
@@ -2255,9 +2365,16 @@ static int r5l_recovery_log(struct r5l_log *log)
 	if (!ctx.meta_page)
 		return -ENOMEM;
 
+	if (r5l_recovery_allocate_ra_pool(log, &ctx) != 0) {
+		__free_page(ctx.meta_page);
+		return -ENOMEM;
+	}
+
 	ret = r5c_recovery_flush_log(log, &ctx);
+	r5l_recovery_free_ra_pool(log, &ctx);
 	__free_page(ctx.meta_page);
 
+
 	if (ret)
 		return ret;
 
-- 
2.9.3