linux/fs/xfs/xfs_aops.h
Dave Chinner e10de3723c xfs: don't chain ioends during writepage submission
Currently we can build a long ioend chain during ->writepages that
gets attached to the writepage context. IO submission only then
occurs when we finish all the writepage processing. This means we
can have many ioends allocated and pending, and this violates the
mempool guarantees that we need to give about forwards progress.
i.e. we really should only have one ioend being built at a time,
otherwise we may drain the mempool trying to allocate a new ioend
and that blocks submission, completion and freeing of ioends that
are already in progress.

To prevent this situation from happening, we need to submit ioends
for IO as soon as they are ready for dispatch rather than queuing
them for later submission. This means the ioends have bios built
immediately and they get queued on any plug that is current active.
Hence if we schedule away from writeback, the ioends that have been
built will make forwards progress due to the plug flushing on
context switch. This will also prevent context switches from
creating unnecessary IO submission latency.

We can't completely avoid having nested IO allocation - when we have
a block size smaller than a page size, we still need to hold the
ioend submission until after we have marked the current page dirty.
Hence we may need multiple ioends to be held while the current page
is completely mapped and made ready for IO dispatch. We cannot avoid
this problem - the current code already has this ioend chaining
within a page so we can mostly ignore that it occurs.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Dave Chinner <david@fromorbit.com>
2016-02-15 17:23:12 +11:00

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2.5 KiB
C

/*
* Copyright (c) 2005-2006 Silicon Graphics, Inc.
* All Rights Reserved.
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License as
* published by the Free Software Foundation.
*
* This program is distributed in the hope that it would be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
*/
#ifndef __XFS_AOPS_H__
#define __XFS_AOPS_H__
extern mempool_t *xfs_ioend_pool;
/*
* Types of I/O for bmap clustering and I/O completion tracking.
*/
enum {
XFS_IO_INVALID, /* initial state */
XFS_IO_DELALLOC, /* covers delalloc region */
XFS_IO_UNWRITTEN, /* covers allocated but uninitialized data */
XFS_IO_OVERWRITE, /* covers already allocated extent */
};
#define XFS_IO_TYPES \
{ XFS_IO_INVALID, "invalid" }, \
{ XFS_IO_DELALLOC, "delalloc" }, \
{ XFS_IO_UNWRITTEN, "unwritten" }, \
{ XFS_IO_OVERWRITE, "overwrite" }
/*
* xfs_ioend struct manages large extent writes for XFS.
* It can manage several multi-page bio's at once.
*/
typedef struct xfs_ioend {
struct list_head io_list; /* next ioend in chain */
unsigned int io_type; /* delalloc / unwritten */
int io_error; /* I/O error code */
atomic_t io_remaining; /* hold count */
struct inode *io_inode; /* file being written to */
struct buffer_head *io_buffer_head;/* buffer linked list head */
struct buffer_head *io_buffer_tail;/* buffer linked list tail */
size_t io_size; /* size of the extent */
xfs_off_t io_offset; /* offset in the file */
struct work_struct io_work; /* xfsdatad work queue */
struct xfs_trans *io_append_trans;/* xact. for size update */
} xfs_ioend_t;
extern const struct address_space_operations xfs_address_space_operations;
int xfs_get_blocks(struct inode *inode, sector_t offset,
struct buffer_head *map_bh, int create);
int xfs_get_blocks_direct(struct inode *inode, sector_t offset,
struct buffer_head *map_bh, int create);
int xfs_get_blocks_dax_fault(struct inode *inode, sector_t offset,
struct buffer_head *map_bh, int create);
extern void xfs_count_page_state(struct page *, int *, int *);
#endif /* __XFS_AOPS_H__ */