The patch titled
Subject: mm: introduce ->swap_rw and use it for reads from SWP_FS_OPS swap-space
has been added to the -mm tree. Its filename is
mm-introduce-swap_rw-and-use-it-for-reads-from-swp_fs_ops-swap-space.patch
This patch should soon appear at
https://ozlabs.org/~akpm/mmots/broken-out/mm-introduce-swap_rw-and-use-it-for-reads-from-swp_fs_ops-swap-space.patch
and later at
https://ozlabs.org/~akpm/mmotm/broken-out/mm-introduce-swap_rw-and-use-it-for-reads-from-swp_fs_ops-swap-space.patch
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------------------------------------------------------
From: NeilBrown <neilb@xxxxxxx>
Subject: 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@xxxxxxx>
Reviewed-by: Christoph Hellwig <hch@xxxxxx>
Cc: David Howells <dhowells@xxxxxxxxxx>
Cc: Hugh Dickins <hughd@xxxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx>
Cc: Trond Myklebust <trond.myklebust@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/cifs/file.c | 4 ++
fs/nfs/file.c | 4 ++
include/linux/fs.h | 1
mm/page_io.c | 68 +++++++++++++++++++++++++++++++++++++++----
mm/swap.h | 1
mm/swapfile.c | 5 +++
6 files changed, 77 insertions(+), 6 deletions(-)
--- a/fs/cifs/file.c~mm-introduce-swap_rw-and-use-it-for-reads-from-swp_fs_ops-swap-space
+++ a/fs/cifs/file.c
@@ -4899,6 +4899,10 @@ static int cifs_swap_activate(struct swa
cifs_dbg(FYI, "swap activate\n");
+ if (!swap_file->f_mapping->a_ops->swap_rw)
+ /* Cannot support swap */
+ return -EINVAL;
+
spin_lock(&inode->i_lock);
blocks = inode->i_blocks;
isize = inode->i_size;
--- a/fs/nfs/file.c~mm-introduce-swap_rw-and-use-it-for-reads-from-swp_fs_ops-swap-space
+++ a/fs/nfs/file.c
@@ -488,6 +488,10 @@ static int nfs_swap_activate(struct swap
struct rpc_clnt *clnt = NFS_CLIENT(inode);
struct nfs_client *cl = NFS_SERVER(inode)->nfs_client;
+ if (!file->f_mapping->a_ops->swap_rw)
+ /* Cannot support swap */
+ return -EINVAL;
+
spin_lock(&inode->i_lock);
blocks = inode->i_blocks;
isize = inode->i_size;
--- a/include/linux/fs.h~mm-introduce-swap_rw-and-use-it-for-reads-from-swp_fs_ops-swap-space
+++ a/include/linux/fs.h
@@ -409,6 +409,7 @@ struct address_space_operations {
int (*swap_activate)(struct swap_info_struct *sis, struct file *file,
sector_t *span);
void (*swap_deactivate)(struct file *file);
+ int (*swap_rw)(struct kiocb *iocb, struct iov_iter *iter);
};
extern const struct address_space_operations empty_aops;
--- a/mm/page_io.c~mm-introduce-swap_rw-and-use-it-for-reads-from-swp_fs_ops-swap-space
+++ a/mm/page_io.c
@@ -235,6 +235,25 @@ static void bio_associate_blkg_from_page
#define bio_associate_blkg_from_page(bio, page) do { } while (0)
#endif /* CONFIG_MEMCG && CONFIG_BLK_CGROUP */
+struct swap_iocb {
+ struct kiocb iocb;
+ struct bio_vec bvec;
+};
+static mempool_t *sio_pool;
+
+int sio_pool_init(void)
+{
+ if (!sio_pool) {
+ mempool_t *pool = mempool_create_kmalloc_pool(
+ SWAP_CLUSTER_MAX, sizeof(struct swap_iocb));
+ if (cmpxchg(&sio_pool, NULL, pool))
+ mempool_destroy(pool);
+ }
+ if (!sio_pool)
+ return -ENOMEM;
+ return 0;
+}
+
int __swap_writepage(struct page *page, struct writeback_control *wbc,
bio_end_io_t end_write_func)
{
@@ -306,6 +325,48 @@ int __swap_writepage(struct page *page,
return 0;
}
+static void sio_read_complete(struct kiocb *iocb, long ret)
+{
+ struct swap_iocb *sio = container_of(iocb, struct swap_iocb, iocb);
+ struct page *page = sio->bvec.bv_page;
+
+ if (ret != 0 && ret != PAGE_SIZE) {
+ SetPageError(page);
+ ClearPageUptodate(page);
+ pr_alert_ratelimited("Read-error on swap-device\n");
+ } else {
+ SetPageUptodate(page);
+ count_vm_event(PSWPIN);
+ }
+ unlock_page(page);
+ mempool_free(sio, sio_pool);
+}
+
+static int swap_readpage_fs(struct page *page)
+{
+ struct swap_info_struct *sis = page_swap_info(page);
+ struct file *swap_file = sis->swap_file;
+ struct address_space *mapping = swap_file->f_mapping;
+ struct iov_iter from;
+ struct swap_iocb *sio;
+ loff_t pos = page_file_offset(page);
+ int ret;
+
+ sio = mempool_alloc(sio_pool, GFP_KERNEL);
+ init_sync_kiocb(&sio->iocb, swap_file);
+ sio->iocb.ki_pos = pos;
+ sio->iocb.ki_complete = sio_read_complete;
+ sio->bvec.bv_page = page;
+ sio->bvec.bv_len = PAGE_SIZE;
+ sio->bvec.bv_offset = 0;
+
+ iov_iter_bvec(&from, READ, &sio->bvec, 1, PAGE_SIZE);
+ ret = mapping->a_ops->swap_rw(&sio->iocb, &from);
+ if (ret != -EIOCBQUEUED)
+ sio_read_complete(&sio->iocb, ret);
+ return ret;
+}
+
int swap_readpage(struct page *page, bool synchronous)
{
struct bio *bio;
@@ -334,12 +395,7 @@ int swap_readpage(struct page *page, boo
}
if (data_race(sis->flags & SWP_FS_OPS)) {
- struct file *swap_file = sis->swap_file;
- struct address_space *mapping = swap_file->f_mapping;
-
- ret = mapping->a_ops->readpage(swap_file, page);
- if (!ret)
- count_vm_event(PSWPIN);
+ ret = swap_readpage_fs(page);
goto out;
}
--- a/mm/swapfile.c~mm-introduce-swap_rw-and-use-it-for-reads-from-swp_fs_ops-swap-space
+++ a/mm/swapfile.c
@@ -2247,6 +2247,11 @@ static int setup_swap_extents(struct swa
if (ret < 0)
return ret;
sis->flags |= SWP_ACTIVATED;
+ if ((sis->flags & SWP_FS_OPS) &&
+ sio_pool_init() != 0) {
+ destroy_swap_extents(sis);
+ return -ENOMEM;
+ }
return ret;
}
--- a/mm/swap.h~mm-introduce-swap_rw-and-use-it-for-reads-from-swp_fs_ops-swap-space
+++ a/mm/swap.h
@@ -6,6 +6,7 @@
#include <linux/blk_types.h> /* for bio_end_io_t */
/* linux/mm/page_io.c */
+int sio_pool_init(void);
int swap_readpage(struct page *page, bool do_poll);
int swap_writepage(struct page *page, struct writeback_control *wbc);
void end_swap_bio_write(struct bio *bio);
_
Patches currently in -mm which might be from neilb@xxxxxxx are
mm-create-new-mm-swaph-header-file.patch
mm-drop-swap_dirty_folio.patch
mm-move-responsibility-for-setting-swp_fs_ops-to-swap_activate.patch
mm-reclaim-mustnt-enter-fs-for-swp_fs_ops-swap-space.patch
mm-introduce-swap_rw-and-use-it-for-reads-from-swp_fs_ops-swap-space.patch
mm-perform-async-writes-to-swp_fs_ops-swap-space-using-swap_rw.patch
doc-update-documentation-for-swap_activate-and-swap_rw.patch
mm-submit-multipage-reads-for-swp_fs_ops-swap-space.patch
mm-submit-multipage-write-for-swp_fs_ops-swap-space.patch
vfs-add-fmode_can_odirect-file-flag.patch
mm-discard-__gfp_atomic.patch
