Re: [PATCH 04/15] brd: remove dax support

2017-11-04 Thread Jens Axboe
On 10/31/2017 05:21 PM, Dan Williams wrote:
> 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.

Reviewed-by: Jens Axboe 

-- 
Jens Axboe

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Re: [PATCH 04/15] brd: remove dax support

2017-11-02 Thread Christoph Hellwig
Looks good,

Reviewed-by: Christoph Hellwig 
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[PATCH 04/15] brd: remove dax support

2017-10-31 Thread Dan Williams
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 
Cc: Matthew Wilcox 
Cc: Ross Zwisler 
Signed-off-by: Dan Williams 
---
 drivers/block/Kconfig |   12 -
 drivers/block/brd.c   |   65 -
 2 files changed, 77 deletions(-)

diff --git a/drivers/block/Kconfig b/drivers/block/Kconfig
index 2dfe99b328f8..da8bf0268ade 100644
--- a/drivers/block/Kconfig
+++ b/drivers/block/Kconfig
@@ -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
diff --git a/drivers/block/brd.c b/drivers/block/brd.c
index 2d7178f7754e..b2391bbd7e5a 100644
--- a/drivers/block/brd.c
+++ b/drivers/block/brd.c
@@ -20,11 +20,6 @@
 #include 
 #include 
 #include 
-#ifdef CONFIG_BLK_DEV_RAM_DAX
-#include 
-#include 
-#include 
-#endif
 
 #include 
 
@@ -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_headbrd_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, _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: