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Commit 34a17b12 authored by Minchan Kim's avatar Minchan Kim Committed by Peter Kalauskas
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BACKPORT: zram: set BDI_CAP_STABLE_WRITES once 

With fast swap storage, the platform wants to use swap more aggressively
and swap-in is crucial to application latency.

The rw_page() based synchronous devices like zram, pmem and btt are such
fast storage.  When I profile swapin performance with zram lz4
decompress test, S/W overhead is more than 70%.  Maybe, it would be
bigger in nvdimm.

This patchset reduces swap-in latency by skipping swapcache if the swap
device is a synchronous device like a rw_page() based device.

It enhances by 45% my swapin test (5G sequential swapin, no readahead)
from 2.41sec to 1.64sec.

This patch (of 4):

Commit 19b7ccf8651d ("block: get rid of blk_integrity_revalidate()")
fixed a weird thing (i.e., reset BDI_CAP_STABLE_WRITES flag
unconditionally whenever revalidat_disk is called) so zram doesn't need
to reset the flag any more when revalidating the bdev.  Instead, set the
flag just once when the zram device is created.

It shouldn't change any behavior.

Link: http://lkml.kernel.org/r/1505886205-9671-2-git-send-email-minchan@kernel.org


Signed-off-by: default avatarMinchan Kim <minchan@kernel.org>
Reviewed-by: default avatarSergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Ilya Dryomov <idryomov@gmail.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Hugh Dickins <hughd@google.com>
Cc: Huang Ying <ying.huang@intel.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>

(cherry picked from commit e447a0151f7ce8dd884fea48279274bd64434c29)
Signed-off-by: default avatarPeter Kalauskas <peskal@google.com>
Bug: 112488418
Change-Id: I59c9006094cec4e6628b5d8f1ae32c6d81f9e365
parent 856f5340

drivers/block/zram/zram_drv.c

+6 −10
Original line number Diff line number Diff line
@@ -121,14 +121,6 @@ static inline bool is_partial_io(struct bio_vec *bvec) 
}

#endif



static void zram_revalidate_disk(struct zram *zram)

{

	revalidate_disk(zram->disk);

	/* revalidate_disk reset the BDI_CAP_STABLE_WRITES so set again */

	zram->disk->queue->backing_dev_info.capabilities |=

		BDI_CAP_STABLE_WRITES;

}



/*

 * Check if request is within bounds and aligned on zram logical blocks.

 */
@@ -1381,7 +1373,8 @@ static ssize_t disksize_store(struct device *dev, 
	zram->comp = comp;

	zram->disksize = disksize;

	set_capacity(zram->disk, zram->disksize >> SECTOR_SHIFT);

	zram_revalidate_disk(zram);



	revalidate_disk(zram->disk);

	up_write(&zram->init_lock);



	return len;
@@ -1428,7 +1421,7 @@ static ssize_t reset_store(struct device *dev, 
	/* Make sure all the pending I/O are finished */

	fsync_bdev(bdev);

	zram_reset_device(zram);

	zram_revalidate_disk(zram);

	revalidate_disk(zram->disk);

	bdput(bdev);



	mutex_lock(&bdev->bd_mutex);
@@ -1547,6 +1540,7 @@ static int zram_add(void) 
	/* zram devices sort of resembles non-rotational disks */

	queue_flag_set_unlocked(QUEUE_FLAG_NONROT, zram->disk->queue);

	queue_flag_clear_unlocked(QUEUE_FLAG_ADD_RANDOM, zram->disk->queue);



	/*

	 * To ensure that we always get PAGE_SIZE aligned

	 * and n*PAGE_SIZED sized I/O requests.
@@ -1572,6 +1566,8 @@ static int zram_add(void) 
		zram->disk->queue->limits.discard_zeroes_data = 0;

	queue_flag_set_unlocked(QUEUE_FLAG_DISCARD, zram->disk->queue);



	zram->disk->queue->backing_dev_info.capabilities |=

					BDI_CAP_STABLE_WRITES;

	add_disk(zram->disk);



	ret = sysfs_create_group(&disk_to_dev(zram->disk)->kobj,