Hi Willy, Trond, Christoph, Here's v3 of a change to make reads and writes from the swapfile use async DIO, adding a new ->swap_rw() address_space method, rather than readpage() or direct_IO(), as requested by Willy. This allows NFS to bypass the write checks that prevent swapfiles from working, plus a bunch of other checks that may or may not be necessary. Whilst trying to make this work, I found that NFS's support for swapfiles seems to have been non-functional since Aug 2019 (I think), so the first patch fixes that. Question is: do we actually *want* to keep this functionality, given that it seems that no one's tested it with an upstream kernel in the last couple of years? There are additional patches to get rid of noop_direct_IO and replace it with a feature bitmask, to make btrfs, ext4, xfs and raw blockdevs use the new ->swap_rw method and thence remove the direct BIO submission paths from swap. I kept the IOCB_SWAP flag, using it to enable REQ_SWAP. I'm not sure if that's necessary, but it seems accounting related. The synchronous DIO I/O code on NFS, raw blockdev, ext4 swapfile and xfs swapfile all seem to work fine. Btrfs refuses to swapon because the file might be CoW'd. I've tried doing "chattr +C", but that didn't help. The async DIO paths fail spectacularly (from I/O errors to ATA failure messages on the test disk using a normal swapspace); NFS just hangs. My patches can be found here also: https://git.kernel.org/pub/scm/linux/kernel/git/dhowells/linux-fs.git/log/?h=swap-dio I tested this using the procedure and program outlined in the NFS patch. I also encountered occasional instances of the following warning with NFS, so I'm wondering if there's a scheduling problem somewhere: BUG: workqueue lockup - pool cpus=0-3 flags=0x5 nice=0 stuck for 34s! Showing busy workqueues and worker pools: workqueue events: flags=0x0 pwq 6: cpus=3 node=0 flags=0x0 nice=0 active=1/256 refcnt=2 in-flight: 1565:fill_page_cache_func workqueue events_highpri: flags=0x10 pwq 3: cpus=1 node=0 flags=0x1 nice=-20 active=1/256 refcnt=2 in-flight: 1547:fill_page_cache_func pwq 1: cpus=0 node=0 flags=0x0 nice=-20 active=1/256 refcnt=2 in-flight: 1811:fill_page_cache_func workqueue events_unbound: flags=0x2 pwq 8: cpus=0-3 flags=0x5 nice=0 active=3/512 refcnt=5 pending: fsnotify_connector_destroy_workfn, fsnotify_mark_destroy_workfn, cleanup_offline_cgwbs_workfn workqueue events_power_efficient: flags=0x82 pwq 8: cpus=0-3 flags=0x5 nice=0 active=4/256 refcnt=6 pending: neigh_periodic_work, neigh_periodic_work, check_lifetime, do_cache_clean workqueue writeback: flags=0x4a pwq 8: cpus=0-3 flags=0x5 nice=0 active=1/256 refcnt=4 in-flight: 433(RESCUER):wb_workfn workqueue rpciod: flags=0xa pwq 8: cpus=0-3 flags=0x5 nice=0 active=38/256 refcnt=40 in-flight: 7:rpc_async_schedule, 1609:rpc_async_schedule, 1610:rpc_async_schedule, 912:rpc_async_schedule, 1613:rpc_async_schedule, 1631:rpc_async_schedule, 34:rpc_async_schedule, 44:rpc_async_schedule pending: rpc_async_schedule, rpc_async_schedule, rpc_async_schedule, rpc_async_schedule, rpc_async_schedule, rpc_async_schedule, rpc_async_schedule, rpc_async_schedule, rpc_async_schedule, rpc_async_schedule, rpc_async_schedule, rpc_async_schedule, rpc_async_schedule, rpc_async_schedule, rpc_async_schedule, rpc_async_schedule, rpc_async_schedule, rpc_async_schedule, rpc_async_schedule, rpc_async_schedule, rpc_async_schedule, rpc_async_schedule, rpc_async_schedule, rpc_async_schedule, rpc_async_schedule, rpc_async_schedule, rpc_async_schedule, rpc_async_schedule, rpc_async_schedule, rpc_async_schedule workqueue ext4-rsv-conversion: flags=0x2000a pool 1: cpus=0 node=0 flags=0x0 nice=-20 hung=59s workers=2 idle: 6 pool 3: cpus=1 node=0 flags=0x1 nice=-20 hung=43s workers=2 manager: 20 pool 6: cpus=3 node=0 flags=0x0 nice=0 hung=0s workers=3 idle: 498 29 pool 8: cpus=0-3 flags=0x5 nice=0 hung=34s workers=9 manager: 1623 pool 9: cpus=0-3 flags=0x5 nice=-20 hung=0s workers=2 manager: 5224 idle: 859 Note that this is due to DIO writes to NFS only, as far as I can tell, and that no reads had happened yet. Changes: ======== ver #3: - Introduced a new ->swap_rw() method. - Added feature support flags to the address_space_operations struct and got rid of the checks for ->direct_() and noop_direct_IO() and similar. - Implemented swap_rw for nfs, adjusting the direct I/O code paths. - Implemented swap_rw for blockdev, btrfs, ext4 and xfs. - Got rid of the return value on swap_readpage() as it's never checked. ver #2: - Remove the callback param to __swap_writepage() as it's invariant. - Allocate the kiocb on the stack in sync mode. - Do an async DIO write if WB_SYNC_ALL isn't set. - Try to remove the BIO submission paths. David Link: https://lore.kernel.org/r/162876946134.3068428.15475611190876694695.stgit@xxxxxxxxxxxxxxxxxxxxxx/ # v1 Link: https://lore.kernel.org/r/162879971699.3306668.8977537647318498651.stgit@xxxxxxxxxxxxxxxxxxxxxx/ # v2 --- David Howells (9): mm: Remove the callback func argument from __swap_writepage() mm: Add 'supports' field to the address_space_operations to list features mm: Make swap_readpage() void Introduce IOCB_SWAP kiocb flag to trigger REQ_SWAP mm: Make swap_readpage() for SWP_FS_OPS use ->swap_rw() not ->readpage() mm: Make __swap_writepage() do async DIO if asked for it nfs: Fix write to swapfile failure due to generic_write_checks() block, btrfs, ext4, xfs: Implement swap_rw mm: Remove swap BIO paths and only use DIO paths Documentation/filesystems/vfs.rst | 8 + block/fops.c | 2 + drivers/block/loop.c | 6 +- fs/9p/vfs_addr.c | 1 + fs/affs/file.c | 1 + fs/btrfs/inode.c | 14 +- fs/ceph/addr.c | 13 +- fs/cifs/file.c | 21 +- fs/direct-io.c | 2 + fs/erofs/data.c | 2 +- fs/exfat/inode.c | 1 + fs/ext2/inode.c | 4 +- fs/ext4/inode.c | 17 +- fs/f2fs/data.c | 1 + fs/fat/inode.c | 1 + fs/fcntl.c | 2 +- fs/fuse/dax.c | 2 +- fs/fuse/file.c | 1 + fs/gfs2/aops.c | 2 +- fs/hfs/inode.c | 1 + fs/hfsplus/inode.c | 1 + fs/jfs/inode.c | 1 + fs/libfs.c | 12 - fs/nfs/direct.c | 28 +-- fs/nfs/file.c | 15 +- fs/nilfs2/inode.c | 1 + fs/ntfs3/inode.c | 1 + fs/ocfs2/aops.c | 1 + fs/open.c | 3 +- fs/orangefs/inode.c | 1 + fs/overlayfs/file.c | 2 +- fs/overlayfs/inode.c | 3 +- fs/reiserfs/inode.c | 1 + fs/udf/file.c | 1 + fs/udf/inode.c | 1 + fs/xfs/xfs_aops.c | 13 +- fs/zonefs/super.c | 2 +- include/linux/bio.h | 2 + include/linux/fs.h | 7 +- include/linux/nfs_fs.h | 2 +- include/linux/swap.h | 2 +- mm/page_io.c | 356 +++++++++++++++--------------- mm/swapfile.c | 4 +- 43 files changed, 275 insertions(+), 287 deletions(-)
