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Commit 7a862fbb authored by Dan Williams's avatar Dan Williams
Browse files

brd: remove dax support 



DAX support in brd is awkward because its backing page frames are
distinct from the ones provided by pmem, dcssblk, or axonram. We need
pfn_t_devmap() entries to fully support DAX, and the limited DAX support
for pfn_t_special() page frames is not interesting for brd when pmem is
already a superset of brd.  Lastly, brd is the only dax capable driver
that may sleep in its ->direct_access() implementation. So it causes a
global burden with no net gain of kernel functionality.

For all these reasons, remove DAX support.

Cc: Jens Axboe <axboe@kernel.dk>
Cc: Matthew Wilcox <mawilcox@microsoft.com>
Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
Reviewed-by: default avatarChristoph Hellwig <hch@lst.de>
Signed-off-by: default avatarDan Williams <dan.j.williams@intel.com>
parent 66a86cc1

drivers/block/Kconfig

+0 −12
Original line number Diff line number Diff line
@@ -297,7 +297,6 @@ config BLK_DEV_SX8 


config BLK_DEV_RAM

	tristate "RAM block device support"

	select DAX if BLK_DEV_RAM_DAX

	---help---

	  Saying Y here will allow you to use a portion of your RAM memory as

	  a block device, so that you can make file systems on it, read and
@@ -333,17 +332,6 @@ config BLK_DEV_RAM_SIZE 
	  The default value is 4096 kilobytes. Only change this if you know

	  what you are doing.



config BLK_DEV_RAM_DAX

	bool "Support Direct Access (DAX) to RAM block devices"

	depends on BLK_DEV_RAM && FS_DAX

	default n

	help

	  Support filesystems using DAX to access RAM block devices.  This

	  avoids double-buffering data in the page cache before copying it

	  to the block device.  Answering Y will slightly enlarge the kernel,

	  and will prevent RAM block device backing store memory from being

	  allocated from highmem (only a problem for highmem systems).



config CDROM_PKTCDVD

	tristate "Packet writing on CD/DVD media (DEPRECATED)"

	depends on !UML

drivers/block/brd.c

+0 −65
Original line number Diff line number Diff line
@@ -20,11 +20,6 @@ 
#include <linux/radix-tree.h>

#include <linux/fs.h>

#include <linux/slab.h>

#ifdef CONFIG_BLK_DEV_RAM_DAX

#include <linux/pfn_t.h>

#include <linux/dax.h>

#include <linux/uio.h>

#endif



#include <linux/uaccess.h>
@@ -44,9 +39,6 @@ struct brd_device { 


	struct request_queue	*brd_queue;

	struct gendisk		*brd_disk;

#ifdef CONFIG_BLK_DEV_RAM_DAX

	struct dax_device	*dax_dev;

#endif

	struct list_head	brd_list;



	/*
@@ -112,9 +104,6 @@ static struct page *brd_insert_page(struct brd_device *brd, sector_t sector) 
	 * restriction might be able to be lifted.

	 */

	gfp_flags = GFP_NOIO | __GFP_ZERO;

#ifndef CONFIG_BLK_DEV_RAM_DAX

	gfp_flags |= __GFP_HIGHMEM;

#endif

	page = alloc_page(gfp_flags);

	if (!page)

		return NULL;
@@ -334,43 +323,6 @@ static int brd_rw_page(struct block_device *bdev, sector_t sector, 
	return err;

}



#ifdef CONFIG_BLK_DEV_RAM_DAX

static long __brd_direct_access(struct brd_device *brd, pgoff_t pgoff,

		long nr_pages, void **kaddr, pfn_t *pfn)

{

	struct page *page;



	if (!brd)

		return -ENODEV;

	page = brd_insert_page(brd, (sector_t)pgoff << PAGE_SECTORS_SHIFT);

	if (!page)

		return -ENOSPC;

	*kaddr = page_address(page);

	*pfn = page_to_pfn_t(page);



	return 1;

}



static long brd_dax_direct_access(struct dax_device *dax_dev,

		pgoff_t pgoff, long nr_pages, void **kaddr, pfn_t *pfn)

{

	struct brd_device *brd = dax_get_private(dax_dev);



	return __brd_direct_access(brd, pgoff, nr_pages, kaddr, pfn);

}



static size_t brd_dax_copy_from_iter(struct dax_device *dax_dev, pgoff_t pgoff,

		void *addr, size_t bytes, struct iov_iter *i)

{

	return copy_from_iter(addr, bytes, i);

}



static const struct dax_operations brd_dax_ops = {

	.direct_access = brd_dax_direct_access,

	.copy_from_iter = brd_dax_copy_from_iter,

};

#endif



static const struct block_device_operations brd_fops = {

	.owner =		THIS_MODULE,

	.rw_page =		brd_rw_page,
@@ -450,21 +402,8 @@ static struct brd_device *brd_alloc(int i) 
	sprintf(disk->disk_name, "ram%d", i);

	set_capacity(disk, rd_size * 2);



#ifdef CONFIG_BLK_DEV_RAM_DAX

	queue_flag_set_unlocked(QUEUE_FLAG_DAX, brd->brd_queue);

	brd->dax_dev = alloc_dax(brd, disk->disk_name, &brd_dax_ops);

	if (!brd->dax_dev)

		goto out_free_inode;

#endif





	return brd;



#ifdef CONFIG_BLK_DEV_RAM_DAX

out_free_inode:

	kill_dax(brd->dax_dev);

	put_dax(brd->dax_dev);

#endif

out_free_queue:

	blk_cleanup_queue(brd->brd_queue);

out_free_dev:
@@ -504,10 +443,6 @@ static struct brd_device *brd_init_one(int i, bool *new) 
static void brd_del_one(struct brd_device *brd)

{

	list_del(&brd->brd_list);

#ifdef CONFIG_BLK_DEV_RAM_DAX

	kill_dax(brd->dax_dev);

	put_dax(brd->dax_dev);

#endif

	del_gendisk(brd->brd_disk);

	brd_free(brd);

}