[06/14] block: lift setting the readahead size into the block layer
diff mbox series

Message ID 20200722062552.212200-7-hch@lst.de
State New
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Series
  • [01/14] fs: remove the unused SB_I_MULTIROOT flag
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Commit Message

Christoph Hellwig July 22, 2020, 6:25 a.m. UTC
Drivers shouldn't really mess with the readahead size, as that is a VM
concept.  Instead set it based on the optimal I/O size by lifting the
algorithm from the md driver when registering the disk.  Also set
bdi->io_pages there as well by applying the same scheme based on
max_sectors.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 block/blk-settings.c         |  5 ++---
 block/blk-sysfs.c            |  1 -
 block/genhd.c                | 13 +++++++++++--
 drivers/block/aoe/aoeblk.c   |  2 --
 drivers/block/drbd/drbd_nl.c | 12 +-----------
 drivers/md/bcache/super.c    |  4 ----
 drivers/md/dm-table.c        |  3 ---
 drivers/md/raid0.c           | 16 ----------------
 drivers/md/raid10.c          | 24 +-----------------------
 drivers/md/raid5.c           | 13 +------------
 10 files changed, 16 insertions(+), 77 deletions(-)

Comments

Johannes Thumshirn July 22, 2020, 7:13 a.m. UTC | #1
On 22/07/2020 08:27, Christoph Hellwig wrote:
> +	q->backing_dev_info->ra_pages =
> +		max(queue_io_opt(q) * 2 / PAGE_SIZE, VM_READAHEAD_PAGES);

Dumb question, wouldn't a '>> PAGE_SHIFT' be better instead of a potentially 
costly division?

Or aren't we caring at all as it's a) not in the fast-path and b) compilers 
can optimize it to a shift?
Christoph Hellwig July 22, 2020, 7:18 a.m. UTC | #2
On Wed, Jul 22, 2020 at 07:13:54AM +0000, Johannes Thumshirn wrote:
> On 22/07/2020 08:27, Christoph Hellwig wrote:
> > +	q->backing_dev_info->ra_pages =
> > +		max(queue_io_opt(q) * 2 / PAGE_SIZE, VM_READAHEAD_PAGES);
> 
> Dumb question, wouldn't a '>> PAGE_SHIFT' be better instead of a potentially 
> costly division?
> 
> Or aren't we caring at all as it's a) not in the fast-path and b) compilers 
> can optimize it to a shift?

That's my thinking.  If anyone has a strong preference I can change
it.

Patch
diff mbox series

diff --git a/block/blk-settings.c b/block/blk-settings.c
index 76a7e03bcd6cac..01049e9b998f1d 100644
--- a/block/blk-settings.c
+++ b/block/blk-settings.c
@@ -452,6 +452,8 @@  EXPORT_SYMBOL(blk_limits_io_opt);
 void blk_queue_io_opt(struct request_queue *q, unsigned int opt)
 {
 	blk_limits_io_opt(&q->limits, opt);
+	q->backing_dev_info->ra_pages =
+		max(queue_io_opt(q) * 2 / PAGE_SIZE, VM_READAHEAD_PAGES);
 }
 EXPORT_SYMBOL(blk_queue_io_opt);
 
@@ -628,9 +630,6 @@  void disk_stack_limits(struct gendisk *disk, struct block_device *bdev,
 		printk(KERN_NOTICE "%s: Warning: Device %s is misaligned\n",
 		       top, bottom);
 	}
-
-	t->backing_dev_info->io_pages =
-		t->limits.max_sectors >> (PAGE_SHIFT - 9);
 }
 EXPORT_SYMBOL(disk_stack_limits);
 
diff --git a/block/blk-sysfs.c b/block/blk-sysfs.c
index 7dda709f3ccb6f..ce418d9128a0b2 100644
--- a/block/blk-sysfs.c
+++ b/block/blk-sysfs.c
@@ -245,7 +245,6 @@  queue_max_sectors_store(struct request_queue *q, const char *page, size_t count)
 
 	spin_lock_irq(&q->queue_lock);
 	q->limits.max_sectors = max_sectors_kb << 1;
-	q->backing_dev_info->io_pages = max_sectors_kb >> (PAGE_SHIFT - 10);
 	spin_unlock_irq(&q->queue_lock);
 
 	return ret;
diff --git a/block/genhd.c b/block/genhd.c
index 8b1e9f48957cb5..097d4e4bc0b8a2 100644
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -775,6 +775,7 @@  static void __device_add_disk(struct device *parent, struct gendisk *disk,
 			      const struct attribute_group **groups,
 			      bool register_queue)
 {
+	struct request_queue *q = disk->queue;
 	dev_t devt;
 	int retval;
 
@@ -785,7 +786,7 @@  static void __device_add_disk(struct device *parent, struct gendisk *disk,
 	 * registration.
 	 */
 	if (register_queue)
-		elevator_init_mq(disk->queue);
+		elevator_init_mq(q);
 
 	/* minors == 0 indicates to use ext devt from part0 and should
 	 * be accompanied with EXT_DEVT flag.  Make sure all
@@ -815,10 +816,18 @@  static void __device_add_disk(struct device *parent, struct gendisk *disk,
 		disk->flags |= GENHD_FL_SUPPRESS_PARTITION_INFO;
 		disk->flags |= GENHD_FL_NO_PART_SCAN;
 	} else {
-		struct backing_dev_info *bdi = disk->queue->backing_dev_info;
+		struct backing_dev_info *bdi = q->backing_dev_info;
 		struct device *dev = disk_to_dev(disk);
 		int ret;
 
+		/*
+		 * For read-ahead of large files to be effective, we need to
+		 * readahead at least twice the optimal I/O size.
+		 */
+		bdi->ra_pages = max(queue_io_opt(q) * 2 / PAGE_SIZE,
+				    VM_READAHEAD_PAGES);
+		bdi->io_pages = queue_max_sectors(q) >> (PAGE_SHIFT - 9);
+
 		/* Register BDI before referencing it from bdev */
 		dev->devt = devt;
 		ret = bdi_register(bdi, "%u:%u", MAJOR(devt), MINOR(devt));
diff --git a/drivers/block/aoe/aoeblk.c b/drivers/block/aoe/aoeblk.c
index 5ca7216e9e01f3..89b33b402b4e52 100644
--- a/drivers/block/aoe/aoeblk.c
+++ b/drivers/block/aoe/aoeblk.c
@@ -347,7 +347,6 @@  aoeblk_gdalloc(void *vp)
 	mempool_t *mp;
 	struct request_queue *q;
 	struct blk_mq_tag_set *set;
-	enum { KB = 1024, MB = KB * KB, READ_AHEAD = 2 * MB, };
 	ulong flags;
 	int late = 0;
 	int err;
@@ -407,7 +406,6 @@  aoeblk_gdalloc(void *vp)
 	WARN_ON(d->gd);
 	WARN_ON(d->flags & DEVFL_UP);
 	blk_queue_max_hw_sectors(q, BLK_DEF_MAX_SECTORS);
-	q->backing_dev_info->ra_pages = READ_AHEAD / PAGE_SIZE;
 	d->bufpool = mp;
 	d->blkq = gd->queue = q;
 	q->queuedata = d;
diff --git a/drivers/block/drbd/drbd_nl.c b/drivers/block/drbd/drbd_nl.c
index 650372ee2c7822..212bf711fb6b41 100644
--- a/drivers/block/drbd/drbd_nl.c
+++ b/drivers/block/drbd/drbd_nl.c
@@ -1360,18 +1360,8 @@  static void drbd_setup_queue_param(struct drbd_device *device, struct drbd_backi
 	decide_on_discard_support(device, q, b, discard_zeroes_if_aligned);
 	decide_on_write_same_support(device, q, b, o, disable_write_same);
 
-	if (b) {
+	if (b)
 		blk_stack_limits(&q->limits, &b->limits, 0);
-
-		if (q->backing_dev_info->ra_pages !=
-		    b->backing_dev_info->ra_pages) {
-			drbd_info(device, "Adjusting my ra_pages to backing device's (%lu -> %lu)\n",
-				 q->backing_dev_info->ra_pages,
-				 b->backing_dev_info->ra_pages);
-			q->backing_dev_info->ra_pages =
-						b->backing_dev_info->ra_pages;
-		}
-	}
 	fixup_discard_if_not_supported(q);
 	fixup_write_zeroes(device, q);
 }
diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c
index 9e45faa054b6f4..9d3f0711be030f 100644
--- a/drivers/md/bcache/super.c
+++ b/drivers/md/bcache/super.c
@@ -1367,10 +1367,6 @@  static int cached_dev_init(struct cached_dev *dc, unsigned int block_size)
 	if (ret)
 		return ret;
 
-	dc->disk.disk->queue->backing_dev_info->ra_pages =
-		max(dc->disk.disk->queue->backing_dev_info->ra_pages,
-		    q->backing_dev_info->ra_pages);
-
 	atomic_set(&dc->io_errors, 0);
 	dc->io_disable = false;
 	dc->error_limit = DEFAULT_CACHED_DEV_ERROR_LIMIT;
diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
index aac4c31cfc8498..324a42ed2f8894 100644
--- a/drivers/md/dm-table.c
+++ b/drivers/md/dm-table.c
@@ -1924,9 +1924,6 @@  void dm_table_set_restrictions(struct dm_table *t, struct request_queue *q,
 		q->nr_zones = blkdev_nr_zones(t->md->disk);
 	}
 #endif
-
-	/* Allow reads to exceed readahead limits */
-	q->backing_dev_info->io_pages = limits->max_sectors >> (PAGE_SHIFT - 9);
 }
 
 unsigned int dm_table_get_num_targets(struct dm_table *t)
diff --git a/drivers/md/raid0.c b/drivers/md/raid0.c
index f54a449f97aa79..aa2d7279176880 100644
--- a/drivers/md/raid0.c
+++ b/drivers/md/raid0.c
@@ -410,22 +410,6 @@  static int raid0_run(struct mddev *mddev)
 		 mdname(mddev),
 		 (unsigned long long)mddev->array_sectors);
 
-	if (mddev->queue) {
-		/* calculate the max read-ahead size.
-		 * For read-ahead of large files to be effective, we need to
-		 * readahead at least twice a whole stripe. i.e. number of devices
-		 * multiplied by chunk size times 2.
-		 * If an individual device has an ra_pages greater than the
-		 * chunk size, then we will not drive that device as hard as it
-		 * wants.  We consider this a configuration error: a larger
-		 * chunksize should be used in that case.
-		 */
-		int stripe = mddev->raid_disks *
-			(mddev->chunk_sectors << 9) / PAGE_SIZE;
-		if (mddev->queue->backing_dev_info->ra_pages < 2* stripe)
-			mddev->queue->backing_dev_info->ra_pages = 2* stripe;
-	}
-
 	dump_zones(mddev);
 
 	ret = md_integrity_register(mddev);
diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
index 9f88ff9bdee437..23d15acbf457d4 100644
--- a/drivers/md/raid10.c
+++ b/drivers/md/raid10.c
@@ -3865,19 +3865,6 @@  static int raid10_run(struct mddev *mddev)
 	mddev->resync_max_sectors = size;
 	set_bit(MD_FAILFAST_SUPPORTED, &mddev->flags);
 
-	if (mddev->queue) {
-		int stripe = conf->geo.raid_disks *
-			((mddev->chunk_sectors << 9) / PAGE_SIZE);
-
-		/* Calculate max read-ahead size.
-		 * We need to readahead at least twice a whole stripe....
-		 * maybe...
-		 */
-		stripe /= conf->geo.near_copies;
-		if (mddev->queue->backing_dev_info->ra_pages < 2 * stripe)
-			mddev->queue->backing_dev_info->ra_pages = 2 * stripe;
-	}
-
 	if (md_integrity_register(mddev))
 		goto out_free_conf;
 
@@ -4715,17 +4702,8 @@  static void end_reshape(struct r10conf *conf)
 	conf->reshape_safe = MaxSector;
 	spin_unlock_irq(&conf->device_lock);
 
-	/* read-ahead size must cover two whole stripes, which is
-	 * 2 * (datadisks) * chunksize where 'n' is the number of raid devices
-	 */
-	if (conf->mddev->queue) {
-		int stripe = conf->geo.raid_disks *
-			((conf->mddev->chunk_sectors << 9) / PAGE_SIZE);
-		stripe /= conf->geo.near_copies;
-		if (conf->mddev->queue->backing_dev_info->ra_pages < 2 * stripe)
-			conf->mddev->queue->backing_dev_info->ra_pages = 2 * stripe;
+	if (conf->mddev->queue)
 		raid10_set_io_opt(conf);
-	}
 	conf->fullsync = 0;
 }
 
diff --git a/drivers/md/raid5.c b/drivers/md/raid5.c
index 68e41ce3ca75cc..415ce3cc155698 100644
--- a/drivers/md/raid5.c
+++ b/drivers/md/raid5.c
@@ -7413,8 +7413,6 @@  static int raid5_run(struct mddev *mddev)
 		int data_disks = conf->previous_raid_disks - conf->max_degraded;
 		int stripe = data_disks *
 			((mddev->chunk_sectors << 9) / PAGE_SIZE);
-		if (mddev->queue->backing_dev_info->ra_pages < 2 * stripe)
-			mddev->queue->backing_dev_info->ra_pages = 2 * stripe;
 
 		chunk_size = mddev->chunk_sectors << 9;
 		blk_queue_io_min(mddev->queue, chunk_size);
@@ -8002,17 +8000,8 @@  static void end_reshape(struct r5conf *conf)
 		spin_unlock_irq(&conf->device_lock);
 		wake_up(&conf->wait_for_overlap);
 
-		/* read-ahead size must cover two whole stripes, which is
-		 * 2 * (datadisks) * chunksize where 'n' is the number of raid devices
-		 */
-		if (conf->mddev->queue) {
-			int data_disks = conf->raid_disks - conf->max_degraded;
-			int stripe = data_disks * ((conf->chunk_sectors << 9)
-						   / PAGE_SIZE);
-			if (conf->mddev->queue->backing_dev_info->ra_pages < 2 * stripe)
-				conf->mddev->queue->backing_dev_info->ra_pages = 2 * stripe;
+		if (conf->mddev->queue)
 			raid5_set_io_opt(conf);
-		}
 	}
 }