diff options
author | NeilBrown <neilb@suse.de> | 2022-05-09 18:20:48 -0700 |
---|---|---|
committer | akpm <akpm@linux-foundation.org> | 2022-05-09 18:20:48 -0700 |
commit | e1209d3a7a67c281260ba9989621060ba7328b8c (patch) | |
tree | 267b9e527bf7d26db3078fd32ce60447b8e45108 /Documentation/block/writeback_cache_control.rst | |
parent | d791ea676b66489ef6dabd04cd655f5c77426e40 (diff) | |
download | linux-stable-e1209d3a7a67c281260ba9989621060ba7328b8c.tar.gz linux-stable-e1209d3a7a67c281260ba9989621060ba7328b8c.tar.bz2 linux-stable-e1209d3a7a67c281260ba9989621060ba7328b8c.zip |
mm: introduce ->swap_rw and use it for reads from SWP_FS_OPS swap-space
swap currently uses ->readpage to read swap pages. This can only request
one page at a time from the filesystem, which is not most efficient.
swap uses ->direct_IO for writes which while this is adequate is an
inappropriate over-loading. ->direct_IO may need to had handle allocate
space for holes or other details that are not relevant for swap.
So this patch introduces a new address_space operation: ->swap_rw. In
this patch it is used for reads, and a subsequent patch will switch writes
to use it.
No filesystem yet supports ->swap_rw, but that is not a problem because
no filesystem actually works with filesystem-based swap.
Only two filesystems set SWP_FS_OPS:
- cifs sets the flag, but ->direct_IO always fails so swap cannot work.
- nfs sets the flag, but ->direct_IO calls generic_write_checks()
which has failed on swap files for several releases.
To ensure that a NULL ->swap_rw isn't called, ->activate_swap() for both
NFS and cifs are changed to fail if ->swap_rw is not set. This can be
removed if/when the function is added.
Future patches will restore swap-over-NFS functionality.
To submit an async read with ->swap_rw() we need to allocate a structure
to hold the kiocb and other details. swap_readpage() cannot handle
transient failure, so we create a mempool to provide the structures.
Link: https://lkml.kernel.org/r/164859778125.29473.13430559328221330589.stgit@noble.brown
Signed-off-by: NeilBrown <neilb@suse.de>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Tested-by: David Howells <dhowells@redhat.com>
Tested-by: Geert Uytterhoeven <geert+renesas@glider.be>
Cc: Hugh Dickins <hughd@google.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Trond Myklebust <trond.myklebust@hammerspace.com>
Cc: Miaohe Lin <linmiaohe@huawei.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Diffstat (limited to 'Documentation/block/writeback_cache_control.rst')
0 files changed, 0 insertions, 0 deletions