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666daa9f97
In debugging a generic/320 failure on ppc64, Nikolay noticed that sometimes we'd ENOSPC out with plenty of space to reclaim if we had committed the transaction. He further discovered that this was because there was a priority ticket that was small enough to fit in the free space currently in the space_info. Consider the following scenario. There is no more space to reclaim in the fs without committing the transaction. Assume there's 1MiB of space free in the space info, but there are pending normal tickets with 2MiB reservations. Now a priority ticket comes in with a .5MiB reservation. Because we have normal tickets pending we add ourselves to the priority list, despite the fact that we could satisfy this reservation. The flushing machinery now gets to the point where it wants to commit the transaction, but because there's a .5MiB ticket on the priority list and we have 1MiB of free space we assume the ticket will be granted soon, so we bail without committing the transaction. Meanwhile the priority flushing does not commit the transaction, and eventually fails with an ENOSPC. Then all other tickets are failed with ENOSPC because we were never able to actually commit the transaction. The fix for this is we should have simply granted the priority flusher his reservation, because there was space to make the reservation. Priority flushers by definition take priority, so they are allowed to make their reservations before any previous normal tickets. By not adding this priority ticket to the list the normal flushing mechanisms will then commit the transaction and everything will continue normally. We still need to serialize ourselves with other priority tickets, so if there are any tickets on the priority list then we need to add ourselves to that list in order to maintain the serialization between priority tickets. Reviewed-by: Nikolay Borisov <nborisov@suse.com> Tested-by: Nikolay Borisov <nborisov@suse.com> Signed-off-by: Josef Bacik <josef@toxicpanda.com> Signed-off-by: David Sterba <dsterba@suse.com> |
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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 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.