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Commit 1e6563ff authored by Jens Axboe's avatar Jens Axboe Committed by Alistair Strachan
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UPSTREAM: mm: don't cap request size based on read-ahead setting 

We ran into a funky issue, where someone doing 256K buffered reads saw
128K requests at the device level.  Turns out it is read-ahead capping
the request size, since we use 128K as the default setting.  This
doesn't make a lot of sense - if someone is issuing 256K reads, they
should see 256K reads, regardless of the read-ahead setting, if the
underlying device can support a 256K read in a single command.

This patch introduces a bdi hint, io_pages.  This is the soft max IO
size for the lower level, I've hooked it up to the bdev settings here.
Read-ahead is modified to issue the maximum of the user request size,
and the read-ahead max size, but capped to the max request size on the
device side.  The latter is done to avoid reading ahead too much, if the
application asks for a huge read.  With this patch, the kernel behaves
like the application expects.

Change-Id: Ibe52ffac7a6e1ac86ed0c6a59a0f7a32d651ee5f
Link: http://lkml.kernel.org/r/1479498073-8657-1-git-send-email-axboe@fb.com


Signed-off-by: default avatarJens Axboe <axboe@fb.com>
Acked-by: default avatarJohannes Weiner <hannes@cmpxchg.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: default avatarJaegeuk Kim <jaegeuk@google.com>
parent 8f9cdb07

block/blk-settings.c

+1 −0
Original line number Diff line number Diff line
@@ -249,6 +249,7 @@ void blk_queue_max_hw_sectors(struct request_queue *q, unsigned int max_hw_secto 
	max_sectors = min_not_zero(max_hw_sectors, limits->max_dev_sectors);

	max_sectors = min_t(unsigned int, max_sectors, BLK_DEF_MAX_SECTORS);

	limits->max_sectors = max_sectors;

	q->backing_dev_info.io_pages = max_sectors >> (PAGE_SHIFT - 9);

}

EXPORT_SYMBOL(blk_queue_max_hw_sectors);

block/blk-sysfs.c

+1 −0
Original line number Diff line number Diff line
@@ -212,6 +212,7 @@ 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;

include/linux/backing-dev-defs.h

+1 −0
Original line number Diff line number Diff line
@@ -136,6 +136,7 @@ struct bdi_writeback { 
struct backing_dev_info {

	struct list_head bdi_list;

	unsigned long ra_pages;	/* max readahead in PAGE_SIZE units */

	unsigned long io_pages;	/* max allowed IO size */

	unsigned int capabilities; /* Device capabilities */

	congested_fn *congested_fn; /* Function pointer if device is md/dm */

	void *congested_data;	/* Pointer to aux data for congested func */

mm/readahead.c

+28 −11
Original line number Diff line number Diff line
@@ -209,10 +209,19 @@ int __do_page_cache_readahead(struct address_space *mapping, struct file *filp, 
int force_page_cache_readahead(struct address_space *mapping, struct file *filp,

			       pgoff_t offset, unsigned long nr_to_read)

{

	struct backing_dev_info *bdi = inode_to_bdi(mapping->host);

	struct file_ra_state *ra = &filp->f_ra;

	unsigned long max_pages;



	if (unlikely(!mapping->a_ops->readpage && !mapping->a_ops->readpages))

		return -EINVAL;



	nr_to_read = min(nr_to_read, inode_to_bdi(mapping->host)->ra_pages);

	/*

	 * If the request exceeds the readahead window, allow the read to

	 * be up to the optimal hardware IO size

	 */

	max_pages = max_t(unsigned long, bdi->io_pages, ra->ra_pages);

	nr_to_read = min(nr_to_read, max_pages);

	while (nr_to_read) {

		int err;
@@ -369,9 +378,17 @@ ondemand_readahead(struct address_space *mapping, 
		   bool hit_readahead_marker, pgoff_t offset,

		   unsigned long req_size)

{

	unsigned long max = ra->ra_pages;

	struct backing_dev_info *bdi = inode_to_bdi(mapping->host);

	unsigned long max_pages = ra->ra_pages;

	pgoff_t prev_offset;



	/*

	 * If the request exceeds the readahead window, allow the read to

	 * be up to the optimal hardware IO size

	 */

	if (req_size > max_pages && bdi->io_pages > max_pages)

		max_pages = min(req_size, bdi->io_pages);



	/*

	 * start of file

	 */
@@ -385,7 +402,7 @@ ondemand_readahead(struct address_space *mapping, 
	if ((offset == (ra->start + ra->size - ra->async_size) ||

	     offset == (ra->start + ra->size))) {

		ra->start += ra->size;

		ra->size = get_next_ra_size(ra, max);

		ra->size = get_next_ra_size(ra, max_pages);

		ra->async_size = ra->size;

		goto readit;

	}
@@ -400,16 +417,16 @@ ondemand_readahead(struct address_space *mapping, 
		pgoff_t start;



		rcu_read_lock();

		start = page_cache_next_hole(mapping, offset + 1, max);

		start = page_cache_next_hole(mapping, offset + 1, max_pages);

		rcu_read_unlock();



		if (!start || start - offset > max)

		if (!start || start - offset > max_pages)

			return 0;



		ra->start = start;

		ra->size = start - offset;	/* old async_size */

		ra->size += req_size;

		ra->size = get_next_ra_size(ra, max);

		ra->size = get_next_ra_size(ra, max_pages);

		ra->async_size = ra->size;

		goto readit;

	}
@@ -417,7 +434,7 @@ ondemand_readahead(struct address_space *mapping, 
	/*

	 * oversize read

	 */

	if (req_size > max)

	if (req_size > max_pages)

		goto initial_readahead;



	/*
@@ -433,7 +450,7 @@ ondemand_readahead(struct address_space *mapping, 
	 * Query the page cache and look for the traces(cached history pages)

	 * that a sequential stream would leave behind.

	 */

	if (try_context_readahead(mapping, ra, offset, req_size, max))

	if (try_context_readahead(mapping, ra, offset, req_size, max_pages))

		goto readit;



	/*
@@ -444,7 +461,7 @@ ondemand_readahead(struct address_space *mapping, 


initial_readahead:

	ra->start = offset;

	ra->size = get_init_ra_size(req_size, max);

	ra->size = get_init_ra_size(req_size, max_pages);

	ra->async_size = ra->size > req_size ? ra->size - req_size : ra->size;



readit:
@@ -454,7 +471,7 @@ ondemand_readahead(struct address_space *mapping, 
	 * the resulted next readahead window into the current one.

	 */

	if (offset == ra->start && ra->size == ra->async_size) {

		ra->async_size = get_next_ra_size(ra, max);

		ra->async_size = get_next_ra_size(ra, max_pages);

		ra->size += ra->async_size;

	}