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09caeabe1a
Previosuly, the transaction commit path would have to add keys to the btree write buffer as a separate operation, requiring additional global synchronization. This patch introduces a new journal entry type, which indicates that the keys need to be copied into the btree write buffer prior to being written out. We switch the journal entry type back to JSET_ENTRY_btree_keys prior to write, so this is not an on disk format change. Flushing the btree write buffer may require pulling keys out of journal entries yet to be written, and quiescing outstanding journal reservations; we previously added journal->buf_lock for synchronization with the journal write path. We also can't put strict bounds on the number of keys in the journal destined for the write buffer, which means we might overflow the size of the preallocated buffer and have to reallocate - this introduces a potentially fatal memory allocation failure. This is something we'll have to watch for, if it becomes an issue in practice we can do additional mitigation. The transaction commit path no longer has to explicitly check if the write buffer is full and wait on flushing; this is another performance optimization. Instead, when the btree write buffer is close to full we change the journal watermark, so that only reservations for journal reclaim are allowed. 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.