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When creating a snapshot, ordered extents need to be flushed and this
can take a long time.
In create_snapshot there are two locks held when this happens:
1. Destination directory inode lock
2. Global subvolume semaphore
This will unnecessarily block other operations like subvolume destroy,
create, or setflag until the snapshot is created.
We can fix that by moving the flush outside the locked section as this
does not depend on the aforementioned locks. The code factors out the
snapshot related work from create_snapshot to btrfs_mksnapshot.
__btrfs_ioctl_snap_create
btrfs_mksubvol
create_subvol
btrfs_mksnapshot
<flush>
btrfs_mksubvol
create_snapshot
Reviewed-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Robbie Ko <robbieko@synology.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.