New addres_space_operations methods are added:
int swapon(struct file *);
int swapoff(struct file *);
int swap_out(struct file *, struct page *, struct writeback_control *);
int swap_in(struct file *, struct page *);
When during sys_swapon() the ->swapon() method is found and returns no error
the swapper_space.a_ops will proxy to sis->swap_file->f_mapping->a_ops, and
make use of ->swap_{out,in}() to write/read swapcache pages.
The ->swapon() method will be used to communicate to the file that the VM
relies on it, and the address_space should take adequate measures (like
reserving memory for mempools or the like). The ->swapoff() method will be
called on sys_swapoff() when ->swapon() was found and returned no error.
This new interface can be used to obviate the need for ->bmap in the swapfile
code. A filesystem would need to load (and maybe even allocate) the full block
map for a file into memory and pin it there on ->swapon() so that
->swap_{out,in}() have instant access to it. It can be released on ->swapoff().
The reason to provide ->swap_{out,in}() over using {write,read}page() is to
1) make a distinction between swapcache and pagecache pages, and
2) to provide a struct file * for credential context (normally not needed
in the context of writepage, as the page content is normally dirtied
using either of the following interfaces:
write_{begin,end}()
{prepare,commit}_write()
page_mkwrite()
which do have the file context.
[miklos@szeredi.hu: cleanups]
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
---
Documentation/filesystems/Locking | 22 ++++++++++++++++
Documentation/filesystems/vfs.txt | 18 +++++++++++++
include/linux/buffer_head.h | 2 -
include/linux/fs.h | 9 ++++++
include/linux/swap.h | 4 ++
mm/page_io.c | 52 ++++++++++++++++++++++++++++++++++++++
mm/swap_state.c | 4 +-
mm/swapfile.c | 32 ...
