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brd: remove dax support

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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: Christoph Hellwig <hch@lst.de>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
This commit is contained in:
Dan Williams 2017-10-23 10:24:45 -07:00
parent 66a86cc109
commit 7a862fbbde
2 changed files with 0 additions and 77 deletions
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12
drivers/block/Kconfig
View File

@ -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

65
drivers/block/brd.c
View File

@ -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);
}