[10/14] bdi: remove BDI_CAP_SYNCHRONOUS_IO
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Message ID 20200726150333.305527-11-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 26, 2020, 3:03 p.m. UTC
BDI_CAP_SYNCHRONOUS_IO is only checked in the swap code, and used to
decided if ->rw_page can be used on a block device.  Just check up for
the method instead.  The only complication is that zram needs a second
set of block_device_operations as it can switch between modes that
actually support ->rw_page and those who don't.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 drivers/block/brd.c           |  1 -
 drivers/block/zram/zram_drv.c | 19 +++++++++++++------
 drivers/nvdimm/btt.c          |  2 --
 drivers/nvdimm/pmem.c         |  1 -
 include/linux/backing-dev.h   |  9 ---------
 mm/swapfile.c                 |  2 +-
 6 files changed, 14 insertions(+), 20 deletions(-)

Comments

Minchan Kim July 26, 2020, 7:06 p.m. UTC | #1
On Sun, Jul 26, 2020 at 05:03:29PM +0200, Christoph Hellwig wrote:
> BDI_CAP_SYNCHRONOUS_IO is only checked in the swap code, and used to
> decided if ->rw_page can be used on a block device.  Just check up for
> the method instead.  The only complication is that zram needs a second
> set of block_device_operations as it can switch between modes that
> actually support ->rw_page and those who don't.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>  drivers/block/brd.c           |  1 -
>  drivers/block/zram/zram_drv.c | 19 +++++++++++++------
>  drivers/nvdimm/btt.c          |  2 --
>  drivers/nvdimm/pmem.c         |  1 -
>  include/linux/backing-dev.h   |  9 ---------
>  mm/swapfile.c                 |  2 +-
>  6 files changed, 14 insertions(+), 20 deletions(-)
> 
> diff --git a/drivers/block/brd.c b/drivers/block/brd.c
> index 2723a70eb85593..cc49a921339f77 100644
> --- a/drivers/block/brd.c
> +++ b/drivers/block/brd.c
> @@ -403,7 +403,6 @@ static struct brd_device *brd_alloc(int i)
>  	disk->flags		= GENHD_FL_EXT_DEVT;
>  	sprintf(disk->disk_name, "ram%d", i);
>  	set_capacity(disk, rd_size * 2);
> -	brd->brd_queue->backing_dev_info->capabilities |= BDI_CAP_SYNCHRONOUS_IO;
>  
>  	/* Tell the block layer that this is not a rotational device */
>  	blk_queue_flag_set(QUEUE_FLAG_NONROT, brd->brd_queue);
> diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
> index 9100ac36670afc..d73ddf018fa65f 100644
> --- a/drivers/block/zram/zram_drv.c
> +++ b/drivers/block/zram/zram_drv.c
> @@ -52,6 +52,9 @@ static unsigned int num_devices = 1;
>   */
>  static size_t huge_class_size;
>  
> +static const struct block_device_operations zram_devops;
> +static const struct block_device_operations zram_wb_devops;
> +
>  static void zram_free_page(struct zram *zram, size_t index);
>  static int zram_bvec_read(struct zram *zram, struct bio_vec *bvec,
>  				u32 index, int offset, struct bio *bio);
> @@ -408,8 +411,7 @@ static void reset_bdev(struct zram *zram)
>  	zram->backing_dev = NULL;
>  	zram->old_block_size = 0;
>  	zram->bdev = NULL;
> -	zram->disk->queue->backing_dev_info->capabilities |=
> -				BDI_CAP_SYNCHRONOUS_IO;
> +	zram->disk->fops = &zram_devops;
>  	kvfree(zram->bitmap);
>  	zram->bitmap = NULL;
>  }
> @@ -528,8 +530,7 @@ static ssize_t backing_dev_store(struct device *dev,
>  	 * freely but in fact, IO is going on so finally could cause
>  	 * use-after-free when the IO is really done.
>  	 */
> -	zram->disk->queue->backing_dev_info->capabilities &=
> -			~BDI_CAP_SYNCHRONOUS_IO;
> +	zram->disk->fops = &zram_wb_devops;
>  	up_write(&zram->init_lock);

For zram, regardless of BDI_CAP_SYNCHRONOUS_IO, it have used rw_page
every time on read/write path. This one with next patch will make zram
use bio instead of rw_page when it's declared !BDI_CAP_SYNCHRONOUS_IO,
which introduce regression for performance.

In the swap code, BDI_CAP_SYNCHRONOUS_IO is used to avoid swap cache
when the page was private. bdev_read_page is not designed to rely on
synchronous operation. That's why this patch breaks the old behavior.

>  
>  	pr_info("setup backing device %s\n", file_name);
> @@ -1819,6 +1820,13 @@ static const struct block_device_operations zram_devops = {
>  	.owner = THIS_MODULE
>  };
>  
> +static const struct block_device_operations zram_wb_devops = {
> +	.open = zram_open,
> +	.submit_bio = zram_submit_bio,
> +	.swap_slot_free_notify = zram_slot_free_notify,
> +	.owner = THIS_MODULE
> +};
> +
>  static DEVICE_ATTR_WO(compact);
>  static DEVICE_ATTR_RW(disksize);
>  static DEVICE_ATTR_RO(initstate);
> @@ -1946,8 +1954,7 @@ static int zram_add(void)
>  	if (ZRAM_LOGICAL_BLOCK_SIZE == PAGE_SIZE)
>  		blk_queue_max_write_zeroes_sectors(zram->disk->queue, UINT_MAX);
>  
> -	zram->disk->queue->backing_dev_info->capabilities |=
> -			(BDI_CAP_STABLE_WRITES | BDI_CAP_SYNCHRONOUS_IO);
> +	zram->disk->queue->backing_dev_info->capabilities |= BDI_CAP_STABLE_WRITES;
>  	device_add_disk(NULL, zram->disk, zram_disk_attr_groups);
>  
>  	strlcpy(zram->compressor, default_compressor, sizeof(zram->compressor));
> diff --git a/drivers/nvdimm/btt.c b/drivers/nvdimm/btt.c
> index 412d21d8f64351..b4184dc9b41eb4 100644
> --- a/drivers/nvdimm/btt.c
> +++ b/drivers/nvdimm/btt.c
> @@ -1540,8 +1540,6 @@ static int btt_blk_init(struct btt *btt)
>  	btt->btt_disk->private_data = btt;
>  	btt->btt_disk->queue = btt->btt_queue;
>  	btt->btt_disk->flags = GENHD_FL_EXT_DEVT;
> -	btt->btt_disk->queue->backing_dev_info->capabilities |=
> -			BDI_CAP_SYNCHRONOUS_IO;
>  
>  	blk_queue_logical_block_size(btt->btt_queue, btt->sector_size);
>  	blk_queue_max_hw_sectors(btt->btt_queue, UINT_MAX);
> diff --git a/drivers/nvdimm/pmem.c b/drivers/nvdimm/pmem.c
> index 94790e6e0e4ce1..436b83fb24ad61 100644
> --- a/drivers/nvdimm/pmem.c
> +++ b/drivers/nvdimm/pmem.c
> @@ -478,7 +478,6 @@ static int pmem_attach_disk(struct device *dev,
>  	disk->queue		= q;
>  	disk->flags		= GENHD_FL_EXT_DEVT;
>  	disk->private_data	= pmem;
> -	disk->queue->backing_dev_info->capabilities |= BDI_CAP_SYNCHRONOUS_IO;
>  	nvdimm_namespace_disk_name(ndns, disk->disk_name);
>  	set_capacity(disk, (pmem->size - pmem->pfn_pad - pmem->data_offset)
>  			/ 512);
> diff --git a/include/linux/backing-dev.h b/include/linux/backing-dev.h
> index 52583b6f2ea05d..860ea33571bce5 100644
> --- a/include/linux/backing-dev.h
> +++ b/include/linux/backing-dev.h
> @@ -122,9 +122,6 @@ int bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned int max_ratio);
>   * BDI_CAP_NO_WRITEBACK:   Don't write pages back
>   * BDI_CAP_NO_ACCT_WB:     Don't automatically account writeback pages
>   * BDI_CAP_STRICTLIMIT:    Keep number of dirty pages below bdi threshold.
> - *
> - * BDI_CAP_SYNCHRONOUS_IO: Device is so fast that asynchronous IO would be
> - *			   inefficient.
>   */
>  #define BDI_CAP_NO_ACCT_DIRTY	0x00000001
>  #define BDI_CAP_NO_WRITEBACK	0x00000002
> @@ -132,7 +129,6 @@ int bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned int max_ratio);
>  #define BDI_CAP_STABLE_WRITES	0x00000008
>  #define BDI_CAP_STRICTLIMIT	0x00000010
>  #define BDI_CAP_CGROUP_WRITEBACK 0x00000020
> -#define BDI_CAP_SYNCHRONOUS_IO	0x00000040
>  
>  #define BDI_CAP_NO_ACCT_AND_WRITEBACK \
>  	(BDI_CAP_NO_WRITEBACK | BDI_CAP_NO_ACCT_DIRTY | BDI_CAP_NO_ACCT_WB)
> @@ -174,11 +170,6 @@ static inline int wb_congested(struct bdi_writeback *wb, int cong_bits)
>  long congestion_wait(int sync, long timeout);
>  long wait_iff_congested(int sync, long timeout);
>  
> -static inline bool bdi_cap_synchronous_io(struct backing_dev_info *bdi)
> -{
> -	return bdi->capabilities & BDI_CAP_SYNCHRONOUS_IO;
> -}
> -
>  static inline bool bdi_cap_stable_pages_required(struct backing_dev_info *bdi)
>  {
>  	return bdi->capabilities & BDI_CAP_STABLE_WRITES;
> diff --git a/mm/swapfile.c b/mm/swapfile.c
> index 6c26916e95fd4a..18eac97b10e502 100644
> --- a/mm/swapfile.c
> +++ b/mm/swapfile.c
> @@ -3230,7 +3230,7 @@ SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
>  	if (bdi_cap_stable_pages_required(inode_to_bdi(inode)))
>  		p->flags |= SWP_STABLE_WRITES;
>  
> -	if (bdi_cap_synchronous_io(inode_to_bdi(inode)))
> +	if (p->bdev && p->bdev->bd_disk->fops->rw_page)
>  		p->flags |= SWP_SYNCHRONOUS_IO;
>  
>  	if (p->bdev && blk_queue_nonrot(bdev_get_queue(p->bdev))) {
> -- 
> 2.27.0
>
Christoph Hellwig July 27, 2020, 7:58 a.m. UTC | #2
On Sun, Jul 26, 2020 at 12:06:39PM -0700, Minchan Kim wrote:
> > @@ -528,8 +530,7 @@ static ssize_t backing_dev_store(struct device *dev,
> >  	 * freely but in fact, IO is going on so finally could cause
> >  	 * use-after-free when the IO is really done.
> >  	 */
> > -	zram->disk->queue->backing_dev_info->capabilities &=
> > -			~BDI_CAP_SYNCHRONOUS_IO;
> > +	zram->disk->fops = &zram_wb_devops;
> >  	up_write(&zram->init_lock);
> 
> For zram, regardless of BDI_CAP_SYNCHRONOUS_IO, it have used rw_page
> every time on read/write path. This one with next patch will make zram
> use bio instead of rw_page when it's declared !BDI_CAP_SYNCHRONOUS_IO,
> which introduce regression for performance.

It really should not matter, as the overhead of setting up a bio
is minimal.  It also is only used in the legacy mpage buffered I/O
code outside of the swap code, which has so many performance issues on
its own that even if this made a difference it wouldn't matter.

If you want magic treatment for your zram swap code you really need
to integrate it with the swap code instead of burding the block layer
with all this mess.

Patch
diff mbox series

diff --git a/drivers/block/brd.c b/drivers/block/brd.c
index 2723a70eb85593..cc49a921339f77 100644
--- a/drivers/block/brd.c
+++ b/drivers/block/brd.c
@@ -403,7 +403,6 @@  static struct brd_device *brd_alloc(int i)
 	disk->flags		= GENHD_FL_EXT_DEVT;
 	sprintf(disk->disk_name, "ram%d", i);
 	set_capacity(disk, rd_size * 2);
-	brd->brd_queue->backing_dev_info->capabilities |= BDI_CAP_SYNCHRONOUS_IO;
 
 	/* Tell the block layer that this is not a rotational device */
 	blk_queue_flag_set(QUEUE_FLAG_NONROT, brd->brd_queue);
diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 9100ac36670afc..d73ddf018fa65f 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -52,6 +52,9 @@  static unsigned int num_devices = 1;
  */
 static size_t huge_class_size;
 
+static const struct block_device_operations zram_devops;
+static const struct block_device_operations zram_wb_devops;
+
 static void zram_free_page(struct zram *zram, size_t index);
 static int zram_bvec_read(struct zram *zram, struct bio_vec *bvec,
 				u32 index, int offset, struct bio *bio);
@@ -408,8 +411,7 @@  static void reset_bdev(struct zram *zram)
 	zram->backing_dev = NULL;
 	zram->old_block_size = 0;
 	zram->bdev = NULL;
-	zram->disk->queue->backing_dev_info->capabilities |=
-				BDI_CAP_SYNCHRONOUS_IO;
+	zram->disk->fops = &zram_devops;
 	kvfree(zram->bitmap);
 	zram->bitmap = NULL;
 }
@@ -528,8 +530,7 @@  static ssize_t backing_dev_store(struct device *dev,
 	 * freely but in fact, IO is going on so finally could cause
 	 * use-after-free when the IO is really done.
 	 */
-	zram->disk->queue->backing_dev_info->capabilities &=
-			~BDI_CAP_SYNCHRONOUS_IO;
+	zram->disk->fops = &zram_wb_devops;
 	up_write(&zram->init_lock);
 
 	pr_info("setup backing device %s\n", file_name);
@@ -1819,6 +1820,13 @@  static const struct block_device_operations zram_devops = {
 	.owner = THIS_MODULE
 };
 
+static const struct block_device_operations zram_wb_devops = {
+	.open = zram_open,
+	.submit_bio = zram_submit_bio,
+	.swap_slot_free_notify = zram_slot_free_notify,
+	.owner = THIS_MODULE
+};
+
 static DEVICE_ATTR_WO(compact);
 static DEVICE_ATTR_RW(disksize);
 static DEVICE_ATTR_RO(initstate);
@@ -1946,8 +1954,7 @@  static int zram_add(void)
 	if (ZRAM_LOGICAL_BLOCK_SIZE == PAGE_SIZE)
 		blk_queue_max_write_zeroes_sectors(zram->disk->queue, UINT_MAX);
 
-	zram->disk->queue->backing_dev_info->capabilities |=
-			(BDI_CAP_STABLE_WRITES | BDI_CAP_SYNCHRONOUS_IO);
+	zram->disk->queue->backing_dev_info->capabilities |= BDI_CAP_STABLE_WRITES;
 	device_add_disk(NULL, zram->disk, zram_disk_attr_groups);
 
 	strlcpy(zram->compressor, default_compressor, sizeof(zram->compressor));
diff --git a/drivers/nvdimm/btt.c b/drivers/nvdimm/btt.c
index 412d21d8f64351..b4184dc9b41eb4 100644
--- a/drivers/nvdimm/btt.c
+++ b/drivers/nvdimm/btt.c
@@ -1540,8 +1540,6 @@  static int btt_blk_init(struct btt *btt)
 	btt->btt_disk->private_data = btt;
 	btt->btt_disk->queue = btt->btt_queue;
 	btt->btt_disk->flags = GENHD_FL_EXT_DEVT;
-	btt->btt_disk->queue->backing_dev_info->capabilities |=
-			BDI_CAP_SYNCHRONOUS_IO;
 
 	blk_queue_logical_block_size(btt->btt_queue, btt->sector_size);
 	blk_queue_max_hw_sectors(btt->btt_queue, UINT_MAX);
diff --git a/drivers/nvdimm/pmem.c b/drivers/nvdimm/pmem.c
index 94790e6e0e4ce1..436b83fb24ad61 100644
--- a/drivers/nvdimm/pmem.c
+++ b/drivers/nvdimm/pmem.c
@@ -478,7 +478,6 @@  static int pmem_attach_disk(struct device *dev,
 	disk->queue		= q;
 	disk->flags		= GENHD_FL_EXT_DEVT;
 	disk->private_data	= pmem;
-	disk->queue->backing_dev_info->capabilities |= BDI_CAP_SYNCHRONOUS_IO;
 	nvdimm_namespace_disk_name(ndns, disk->disk_name);
 	set_capacity(disk, (pmem->size - pmem->pfn_pad - pmem->data_offset)
 			/ 512);
diff --git a/include/linux/backing-dev.h b/include/linux/backing-dev.h
index 52583b6f2ea05d..860ea33571bce5 100644
--- a/include/linux/backing-dev.h
+++ b/include/linux/backing-dev.h
@@ -122,9 +122,6 @@  int bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned int max_ratio);
  * BDI_CAP_NO_WRITEBACK:   Don't write pages back
  * BDI_CAP_NO_ACCT_WB:     Don't automatically account writeback pages
  * BDI_CAP_STRICTLIMIT:    Keep number of dirty pages below bdi threshold.
- *
- * BDI_CAP_SYNCHRONOUS_IO: Device is so fast that asynchronous IO would be
- *			   inefficient.
  */
 #define BDI_CAP_NO_ACCT_DIRTY	0x00000001
 #define BDI_CAP_NO_WRITEBACK	0x00000002
@@ -132,7 +129,6 @@  int bdi_set_max_ratio(struct backing_dev_info *bdi, unsigned int max_ratio);
 #define BDI_CAP_STABLE_WRITES	0x00000008
 #define BDI_CAP_STRICTLIMIT	0x00000010
 #define BDI_CAP_CGROUP_WRITEBACK 0x00000020
-#define BDI_CAP_SYNCHRONOUS_IO	0x00000040
 
 #define BDI_CAP_NO_ACCT_AND_WRITEBACK \
 	(BDI_CAP_NO_WRITEBACK | BDI_CAP_NO_ACCT_DIRTY | BDI_CAP_NO_ACCT_WB)
@@ -174,11 +170,6 @@  static inline int wb_congested(struct bdi_writeback *wb, int cong_bits)
 long congestion_wait(int sync, long timeout);
 long wait_iff_congested(int sync, long timeout);
 
-static inline bool bdi_cap_synchronous_io(struct backing_dev_info *bdi)
-{
-	return bdi->capabilities & BDI_CAP_SYNCHRONOUS_IO;
-}
-
 static inline bool bdi_cap_stable_pages_required(struct backing_dev_info *bdi)
 {
 	return bdi->capabilities & BDI_CAP_STABLE_WRITES;
diff --git a/mm/swapfile.c b/mm/swapfile.c
index 6c26916e95fd4a..18eac97b10e502 100644
--- a/mm/swapfile.c
+++ b/mm/swapfile.c
@@ -3230,7 +3230,7 @@  SYSCALL_DEFINE2(swapon, const char __user *, specialfile, int, swap_flags)
 	if (bdi_cap_stable_pages_required(inode_to_bdi(inode)))
 		p->flags |= SWP_STABLE_WRITES;
 
-	if (bdi_cap_synchronous_io(inode_to_bdi(inode)))
+	if (p->bdev && p->bdev->bd_disk->fops->rw_page)
 		p->flags |= SWP_SYNCHRONOUS_IO;
 
 	if (p->bdev && blk_queue_nonrot(bdev_get_queue(p->bdev))) {