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b50b4c49d8
Currently the AIL attempts to keep 25% of the "log space" free, where the current used space is tracked by the reserve grant head. That is, it tracks both physical space used plus the amount reserved by transactions in progress. When we start tail pushing, we are trying to make space for new reservations by writing back older metadata and the log is generally physically full of dirty metadata, and reservations for modifications in flight take up whatever space the AIL can physically free up. Hence we don't really need to take into account the reservation space that has been used - we just need to keep the log tail moving as fast as we can to free up space for more reservations to be made. We know exactly how much physical space the journal is consuming in the AIL (i.e. max LSN - min LSN) so we can base push thresholds directly on this state rather than have to look at grant head reservations to determine how much to physically push out of the log. This also allows code that needs to know if log items in the current transaction need to be pushed or re-logged to simply sample the current target - they don't need to calculate the current target themselves. This avoids the need for any locking when doing such checks. Further, moving to a physical target means we don't need "push all until empty semantics" like were introduced in the previous patch. We can now test and clear the "push all" as a one-shot command to set the target to the current head of the AIL. This allows the xfsaild to maximise the use of log space right up to the point where conditions indicate that the xfsaild is not keeping up with load and it needs to work harder, and as soon as those constraints go away (i.e. external code no longer needs everything pushed) the xfsaild will return to maintaining the normal 25% free space thresholds. Signed-off-by: Dave Chinner <dchinner@redhat.com> Reviewed-by: Darrick J. Wong <djwong@kernel.org> Signed-off-by: Chandan Babu R <chandanbabu@kernel.org> |
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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 reStructuredText 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.