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Date: Thu, 16 Oct 2014 15:00:16 +0200
From: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To: Matthew Wilcox <matthew.r.wilcox@...el.com>
Cc: linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
linux-kernel@...r.kernel.org,
Matthew Wilcox <willy@...ux.intel.com>
Subject: Re: [PATCH v11 21/21] brd: Rename XIP to DAX
On 25-Sep-2014 04:33:38 PM, Matthew Wilcox wrote:
> From: Matthew Wilcox <willy@...ux.intel.com>
>
> Since this is relating to FS_XIP, not KERNEL_XIP, it should be called
> DAX instead of XIP.
>
> Signed-off-by: Matthew Wilcox <matthew.r.wilcox@...el.com>
> ---
> drivers/block/Kconfig | 13 +++++++------
> drivers/block/brd.c | 14 +++++++-------
> fs/Kconfig | 4 ++--
> 3 files changed, 16 insertions(+), 15 deletions(-)
>
> diff --git a/drivers/block/Kconfig b/drivers/block/Kconfig
> index 014a1cf..1b8094d 100644
> --- a/drivers/block/Kconfig
> +++ b/drivers/block/Kconfig
> @@ -393,14 +393,15 @@ config BLK_DEV_RAM_SIZE
> The default value is 4096 kilobytes. Only change this if you know
> what you are doing.
>
> -config BLK_DEV_XIP
> - bool "Support XIP filesystems on RAM block device"
> - depends on BLK_DEV_RAM
> +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 XIP filesystems (such as ext2 with XIP support on) on
> - top of block ram device. This will slightly enlarge the kernel, and
> - will prevent RAM block device backing store memory from being
> + 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
> diff --git a/drivers/block/brd.c b/drivers/block/brd.c
> index 78fe510..97c55db 100644
> --- a/drivers/block/brd.c
> +++ b/drivers/block/brd.c
> @@ -97,13 +97,13 @@ static struct page *brd_insert_page(struct brd_device *brd, sector_t sector)
> * Must use NOIO because we don't want to recurse back into the
> * block or filesystem layers from page reclaim.
> *
> - * Cannot support XIP and highmem, because our ->direct_access
> - * routine for XIP must return memory that is always addressable.
> - * If XIP was reworked to use pfns and kmap throughout, this
> + * Cannot support DAX and highmem, because our ->direct_access
> + * routine for DAX must return memory that is always addressable.
> + * If DAX was reworked to use pfns and kmap throughout, this
So this might be an important limitation on x86-32 with PAE, am I
correct ? It should be eventually investigated if anyone still care, but
it does not appear to be a roadblocking limitation.
Thanks,
Mathieu
> * restriction might be able to be lifted.
> */
> gfp_flags = GFP_NOIO | __GFP_ZERO;
> -#ifndef CONFIG_BLK_DEV_XIP
> +#ifndef CONFIG_BLK_DEV_RAM_DAX
> gfp_flags |= __GFP_HIGHMEM;
> #endif
> page = alloc_page(gfp_flags);
> @@ -369,7 +369,7 @@ static int brd_rw_page(struct block_device *bdev, sector_t sector,
> return err;
> }
>
> -#ifdef CONFIG_BLK_DEV_XIP
> +#ifdef CONFIG_BLK_DEV_RAM_DAX
> static long brd_direct_access(struct block_device *bdev, sector_t sector,
> void **kaddr, unsigned long *pfn, long size)
> {
> @@ -388,6 +388,8 @@ static long brd_direct_access(struct block_device *bdev, sector_t sector,
> * file happens to be mapped to the next page of physical RAM */
> return PAGE_SIZE;
> }
> +#else
> +#define brd_direct_access NULL
> #endif
>
> static int brd_ioctl(struct block_device *bdev, fmode_t mode,
> @@ -428,9 +430,7 @@ static const struct block_device_operations brd_fops = {
> .owner = THIS_MODULE,
> .rw_page = brd_rw_page,
> .ioctl = brd_ioctl,
> -#ifdef CONFIG_BLK_DEV_XIP
> .direct_access = brd_direct_access,
> -#endif
> };
>
> /*
> diff --git a/fs/Kconfig b/fs/Kconfig
> index a9eb53d..117900f 100644
> --- a/fs/Kconfig
> +++ b/fs/Kconfig
> @@ -34,7 +34,7 @@ source "fs/btrfs/Kconfig"
> source "fs/nilfs2/Kconfig"
>
> config FS_DAX
> - bool "Direct Access support"
> + bool "Direct Access (DAX) support"
> depends on MMU
> help
> Direct Access (DAX) can be used on memory-backed block devices.
> @@ -45,7 +45,7 @@ config FS_DAX
>
> If you do not have a block device that is capable of using this,
> or if unsure, say N. Saying Y will increase the size of the kernel
> - by about 2kB.
> + by about 5kB.
>
> endif # BLOCK
>
> --
> 2.1.0
>
> --
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>
>
--
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com
Key fingerprint: 2A0B 4ED9 15F2 D3FA 45F5 B162 1728 0A97 8118 6ACF
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