SB_START_PAGEFAULT(9) The Linux VFS SB_START_PAGEFAULT(9)NAME
sb_start_pagefault - get write access to a superblock from a page fault
void sb_start_pagefault(struct super_block * sb);
the super we write to
When a process starts handling write page fault, it should embed the operation into sb_start_pagefault - sb_end_pagefault pair to get
exclusion against file system freezing. This is needed since the page fault is going to dirty a page. This function increments number of
running page faults preventing freezing. If the file system is already frozen, the function waits until the file system is thawed.
Since page fault freeze protection behaves as a lock, users have to preserve ordering of freeze protection and other filesystem locks. It
is advised to put sb_start_pagefault close to mmap_sem in lock ordering. Page fault
HANDLING CODE IMPLIES LOCK DEPENDENCY
mmap_sem -> sb_start_pagefault
COPYRIGHT Kernel Hackers Manual 3.10 June 2014 SB_START_PAGEFAULT(9)
Check Out this Related Man Page
xfs_freeze(8) System Manager's Manual xfs_freeze(8)NAME
xfs_freeze - suspend access to an XFS filesystem
xfs_freeze -f | -u mount-point
xfs_freeze suspends and resumes access to an XFS filesystem (see xfs(5)).
xfs_freeze halts new access to the filesystem and creates a stable image on disk. xfs_freeze is intended to be used with volume managers
and hardware RAID devices that support the creation of snapshots.
The mount-point argument is the pathname of the directory where the filesystem is mounted. The filesystem must be mounted to be frozen
The -f flag requests the specified XFS filesystem to be frozen from new modifications. When this is selected, all ongoing transactions in
the filesystem are allowed to complete, new write system calls are halted, other calls which modify the filesystem are halted, and all
dirty data, metadata, and log information are written to disk. Any process attempting to write to the frozen filesystem will block waiting
for the filesystem to be unfrozen.
Note that even after freezing, the on-disk filesystem can contain information on files that are still in the process of unlinking. These
files will not be unlinked until the filesystem is unfrozen or a clean mount of the snapshot is complete.
The -u flag is used to un-freeze the filesystem and allow operations to continue. Any filesystem modifications that were blocked by the
freeze are unblocked and allowed to complete.
One of -f or -u must be supplied to xfs_freeze.
A copy of a frozen XFS filesystem will usually have the same universally unique identifier (UUID) as the original, and thus may be pre-
vented from being mounted. The XFS nouuid mount option can be used to circumvent this issue.
In Linux kernel version 2.6.29, the interface which XFS uses to freeze and unfreeze was elevated to the VFS, so that this tool can now be
used on many other Linux filesystems.
SEE ALSO xfs(5), lvm(8), mount(8).
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