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To allow for iclog IO device cache flush behaviour to be optimised, we first need to separate out the commit record iclog IO from the rest of the checkpoint so we can wait for the checkpoint IO to complete before we issue the commit record. This separation is only necessary if the commit record is being written into a different iclog to the start of the checkpoint as the upcoming cache flushing changes requires completion ordering against the other iclogs submitted by the checkpoint. If the entire checkpoint and commit is in the one iclog, then they are both covered by the one set of cache flush primitives on the iclog and hence there is no need to separate them for ordering. Otherwise, we need to wait for all the previous iclogs to complete so they are ordered correctly and made stable by the REQ_PREFLUSH that the commit record iclog IO issues. This guarantees that if a reader sees the commit record in the journal, they will also see the entire checkpoint that commit record closes off. This also provides the guarantee that when the commit record IO completes, we can safely unpin all the log items in the checkpoint so they can be written back because the entire checkpoint is stable in the journal. Signed-off-by: Dave Chinner <dchinner@redhat.com> Reviewed-by: Darrick J. Wong <djwong@kernel.org> Reviewed-by: Chandan Babu R <chandanrlinux@gmail.com> Reviewed-by: Brian Foster <bfoster@redhat.com> Reviewed-by: Allison Henderson <allison.henderson@oracle.com> Signed-off-by: Darrick J. Wong <djwong@kernel.org>
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.