Re: [PATCH 22/28] mm: add support for non block device backed swap files

Randy Dunlap
2008-02-20T16:32:08Z

On Wed, 20 Feb 2008 15:46:32 +0100 Peter Zijlstra wrote:

> Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
> ---
> Documentation/filesystems/Locking | 19 +++++++++++++
> Documentation/filesystems/vfs.txt | 17 ++++++++++++
> include/linux/buffer_head.h | 2 -
> include/linux/fs.h | 8 +++++
> include/linux/swap.h | 4 ++
> mm/page_io.c | 52 ++++++++++++++++++++++++++++++++++++++
> mm/swap_state.c | 4 +-
> mm/swapfile.c | 26 ++++++++++++++++++-
> 8 files changed, 128 insertions(+), 4 deletions(-)

> Index: linux-2.6/Documentation/filesystems/Locking
> ===================================================================
> --- linux-2.6.orig/Documentation/filesystems/Locking
> +++ linux-2.6/Documentation/filesystems/Locking

> @@ -291,6 +297,19 @@ cleaned, or an error value if not. Note
> getting mapped back in and redirtied, it needs to be kept locked
> across the entire operation.
>
> + ->swapfile() will be called with a non zero argument on address spaces

non-zero

> +backing non block device backed swapfiles. A return value of zero indicates
> +success. In which case this address space can be used for backing swapspace.

success, in which case

> +The swapspace operations will be proxied to the address space operations.
> +Swapoff will call this method with a zero argument to release the address
> +space.
> +
> + ->swap_out() when swapfile() returned success, this method is used to
> +write the swap page.
> +
> + ->swap_in() when swapfile() returned success, this method is used to
> +read the swap page.
> +
> Note: currently almost all instances of address_space methods are
> using BKL for internal serialization and that's one of the worst sources
> of contention. Normally they are calling library functions (in fs/buffer.c)

> Index: linux-2.6/Documentation/filesystems/vfs.txt
> ===================================================================
> --- linux-2.6.orig/Documentation/filesystems/vfs.txt
> +++ linux-2.6/Documentation/filesystems/vfs.txt
> @@ -728,6 +732,19 @@ struct address_space_operations {
> prevent redirtying the page, it is kept locked during the whole
> operation.
>
> + swapfile: Called with a non-zero argument when swapon is used on a file. A
> + return value of zero indicates success. In which case this

success, in which case this

> + address_space can be used to back swapspace. The swapspace operations
> + will be proxied to this address space's ->swap_{out,in} methods.
> + Swapoff will call this method with a zero argument to release the
> + address space.
> +
> + swap_out: Called to write a swapcache page to a backing store, similar to
> + writepage.
> +
> + swap_in: Called to read a swapcache page from a backing store, similar to
> + readpage.
> +
> The File Object
> ===============

---
~Randy