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freebsd-dev/zfs_config.h.in
Brian Behlendorf 76659dc110 Add backing_device_info per-filesystem 
For a long time now the kernel has been moving away from using the
pdflush daemon to write 'old' dirty pages to disk.  The primary reason
for this is because the pdflush daemon is single threaded and can be
a limiting factor for performance.  Since pdflush sequentially walks
the dirty inode list for each super block any delay in processing can
slow down dirty page writeback for all filesystems.

The replacement for pdflush is called bdi (backing device info).  The
bdi system involves creating a per-filesystem control structure each
with its own private sets of queues to manage writeback.  The advantage
is greater parallelism which improves performance and prevents a single
filesystem from slowing writeback to the others.

For a long time both systems co-existed in the kernel so it wasn't
strictly required to implement the bdi scheme.  However, as of
Linux 2.6.36 kernels the pdflush functionality has been retired.

Since ZFS already bypasses the page cache for most I/O this is only
an issue for mmap(2) writes which must go through the page cache.
Even then adding this missing support for newer kernels was overlooked
because there are other mechanisms which can trigger writeback.

However, there is one critical case where not implementing the bdi
functionality can cause problems.  If an application handles a page
fault it can enter the balance_dirty_pages() callpath.  This will
result in the application hanging until the number of dirty pages in
the system drops below the dirty ratio.

Without a registered backing_device_info for the filesystem the
dirty pages will not get written out.  Thus the application will hang.
As mentioned above this was less of an issue with older kernels because
pdflush would eventually write out the dirty pages.

This change adds a backing_device_info structure to the zfs_sb_t
which is already allocated per-super block.  It is then registered
when the filesystem mounted and unregistered on unmount.  It will
not be registered for mounted snapshots which are read-only.  This
change will result in flush-<pool> thread being dynamically created
and destroyed per-mounted filesystem for writeback.

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #174
2011-08-04 13:37:38 -07:00

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/* zfs_config.h.in. Generated from configure.ac by autoheader. */
/* invalidate_bdev() wants 1 arg */
#undef HAVE_1ARG_INVALIDATE_BDEV
/* bio_end_io_t wants 2 args */
#undef HAVE_2ARGS_BIO_END_IO_T
/* fops->fsync() want 2 args */
#undef HAVE_2ARGS_FSYNC
/* security_inode_init_security wants 6 args */
#undef HAVE_6ARGS_SECURITY_INODE_INIT_SECURITY
/* struct block_device_operations use bdevs */
#undef HAVE_BDEV_BLOCK_DEVICE_OPERATIONS
/* bdev_logical_block_size() is available */
#undef HAVE_BDEV_LOGICAL_BLOCK_SIZE
/* struct super_block has s_bdi */
#undef HAVE_BDI
/* bio_empy_barrier() is defined */
#undef HAVE_BIO_EMPTY_BARRIER
/* REQ_FAILFAST_MASK is defined */
#undef HAVE_BIO_REQ_FAILFAST_MASK
/* BIO_RW_FAILFAST is defined */
#undef HAVE_BIO_RW_FAILFAST
/* BIO_RW_FAILFAST_* are defined */
#undef HAVE_BIO_RW_FAILFAST_DTD
/* BIO_RW_SYNC is defined */
#undef HAVE_BIO_RW_SYNC
/* BIO_RW_SYNCIO is defined */
#undef HAVE_BIO_RW_SYNCIO
/* blkdev_get_by_path() is available */
#undef HAVE_BLKDEV_GET_BY_PATH
/* blk_end_request() is available */
#undef HAVE_BLK_END_REQUEST
/* blk_end_request() is GPL-only */
#undef HAVE_BLK_END_REQUEST_GPL_ONLY
/* blk_fetch_request() is available */
#undef HAVE_BLK_FETCH_REQUEST
/* blk_requeue_request() is available */
#undef HAVE_BLK_REQUEUE_REQUEST
/* blk_rq_bytes() is available */
#undef HAVE_BLK_RQ_BYTES
/* blk_rq_bytes() is GPL-only */
#undef HAVE_BLK_RQ_BYTES_GPL_ONLY
/* blk_rq_pos() is available */
#undef HAVE_BLK_RQ_POS
/* blk_rq_sectors() is available */
#undef HAVE_BLK_RQ_SECTORS
/* check_disk_size_change() is available */
#undef HAVE_CHECK_DISK_SIZE_CHANGE
/* super_block uses const struct xattr_hander */
#undef HAVE_CONST_XATTR_HANDLER
/* xattr_handler->get() wants dentry */
#undef HAVE_DENTRY_XATTR_GET
/* xattr_handler->set() wants dentry */
#undef HAVE_DENTRY_XATTR_SET
/* Define to 1 if you have the <dlfcn.h> header file. */
#undef HAVE_DLFCN_H
/* d_obtain_alias() is available */
#undef HAVE_D_OBTAIN_ALIAS
/* sops->evict_inode() exists */
#undef HAVE_EVICT_INODE
/* kernel defines fmode_t */
#undef HAVE_FMODE_T
/* blk_disk_ro() is available */
#undef HAVE_GET_DISK_RO
/* Define to 1 if licensed under the GPL */
#undef HAVE_GPL_ONLY_SYMBOLS
/* insert_inode_locked() is available */
#undef HAVE_INSERT_INODE_LOCKED
/* Define to 1 if you have the <inttypes.h> header file. */
#undef HAVE_INTTYPES_H
/* result=stropts.h Define to 1 if ioctl() defined in <stropts.h> */
#undef HAVE_IOCTL_IN_STROPTS_H
/* Define to 1 if ioctl() defined in <sys/ioctl.h> */
#undef HAVE_IOCTL_IN_SYS_IOCTL_H
/* Define to 1 if ioctl() defined in <unistd.h> */
#undef HAVE_IOCTL_IN_UNISTD_H
/* kernel defines KOBJ_NAME_LEN */
#undef HAVE_KOBJ_NAME_LEN
/* Define if you have libblkid */
#undef HAVE_LIBBLKID
/* Define if you have selinux */
#undef HAVE_LIBSELINUX
/* Define if you have libuuid */
#undef HAVE_LIBUUID
/* Define to 1 if you have the `z' library (-lz). */
#undef HAVE_LIBZ
/* Define to 1 if you have the <memory.h> header file. */
#undef HAVE_MEMORY_H
/* mount_nodev() is available */
#undef HAVE_MOUNT_NODEV
/* open_bdev_exclusive() is available */
#undef HAVE_OPEN_BDEV_EXCLUSIVE
/* REQ_SYNC is defined */
#undef HAVE_REQ_SYNC
/* rq_for_each_segment() is available */
#undef HAVE_RQ_FOR_EACH_SEGMENT
/* rq_is_sync() is available */
#undef HAVE_RQ_IS_SYNC
/* Define to 1 if you have the <stdint.h> header file. */
#undef HAVE_STDINT_H
/* Define to 1 if you have the <stdlib.h> header file. */
#undef HAVE_STDLIB_H
/* Define to 1 if you have the <strings.h> header file. */
#undef HAVE_STRINGS_H
/* Define to 1 if you have the <string.h> header file. */
#undef HAVE_STRING_H
/* Define to 1 if you have the <sys/stat.h> header file. */
#undef HAVE_SYS_STAT_H
/* Define to 1 if you have the <sys/types.h> header file. */
#undef HAVE_SYS_TYPES_H
/* truncate_setsize() is available */
#undef HAVE_TRUNCATE_SETSIZE
/* Define to 1 if you have the <unistd.h> header file. */
#undef HAVE_UNISTD_H
/* Define if you have zlib */
#undef HAVE_ZLIB
/* Define to the sub-directory in which libtool stores uninstalled libraries.
*/
#undef LT_OBJDIR
/* Define to 1 if NPTL threading implementation includes guard area in stack
allocation */
#undef NPTL_GUARD_WITHIN_STACK
/* Name of package */
#undef PACKAGE
/* Define to the address where bug reports for this package should be sent. */
#undef PACKAGE_BUGREPORT
/* Define to the full name of this package. */
#undef PACKAGE_NAME
/* Define to the full name and version of this package. */
#undef PACKAGE_STRING
/* Define to the one symbol short name of this package. */
#undef PACKAGE_TARNAME
/* Define to the version of this package. */
#undef PACKAGE_VERSION
/* Define to 1 if you have the ANSI C header files. */
#undef STDC_HEADERS
/* Version number of package */
#undef VERSION
/* Define the project alias string. */
#undef ZFS_META_ALIAS
/* Define the project author. */
#undef ZFS_META_AUTHOR
/* Define the project release date. */
#undef ZFS_META_DATA
/* Define the project license. */
#undef ZFS_META_LICENSE
/* Define the libtool library 'age' version information. */
#undef ZFS_META_LT_AGE
/* Define the libtool library 'current' version information. */
#undef ZFS_META_LT_CURRENT
/* Define the libtool library 'revision' version information. */
#undef ZFS_META_LT_REVISION
/* Define the project name. */
#undef ZFS_META_NAME
/* Define the project release. */
#undef ZFS_META_RELEASE
/* Define the project version. */
#undef ZFS_META_VERSION
#undef PACKAGE
#undef PACKAGE_BUGREPORT
#undef PACKAGE_NAME
#undef PACKAGE_STRING
#undef PACKAGE_TARNAME
#undef PACKAGE_VERSION
#undef STDC_HEADERS
#undef VERSION
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