87b0d8d3d0
Recently, journal pre-reservations were removed. They were for reserving space ahead of time in the journal for operations that are required for journal reclaim, e.g. btree key cache flushing and interior node btree updates. Instead we have watermarks - only operations for journal reclaim are allowed when the journal is low on space, and in general we're quite good about doing operations in the order that will free up space in the journal quickest when we're low on space. If we're doing a journal reclaim operation out of order, we usually do it in nonblocking mode if it's not freeing up space at the end of the journal. There's an exceptino though - interior btree node update operations have to be BCH_WATERMARK_reclaim - once they've been started, and they can't be nonblocking. Generally this is fine because they'll only be a very small fraction of transaction commits - but there's an exception, which is during journal replay. Journal replay does many btree operations, but doesn't need to commit them to the journal since they're already in the journal. So killing off of pre-reservation, plus another change to make journal replay more efficient by initially doing the replay in sorted btree order, made it possible for the interior update operations replay generates to fill and deadlock the journal. Fix this by introducing a new check on journal space at the _start_ of an interior update operation. This causes us to block if necessary in exactly the same way as we used to when interior updates took a journal pre-reservaiton, but without all the expensive accounting pre-reservations required. Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
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.