576fa34830
Currently if we ever have to flush space because we do not have enough we allocate a ticket and attach it to the space_info, and then systematically flush things in the filesystem that hold space reservations until our space is reclaimed. However this has a latency cost, we must go to sleep and wait for the flushing to make progress before we are woken up and allowed to continue doing our work. In order to address that we used to kick off the async worker to flush space preemptively, so that we could be reclaiming space hopefully before any tasks needed to stop and wait for space to reclaim. When I introduced the ticketed ENOSPC stuff this broke slightly in the fact that we were using tickets to indicate if we were done flushing. No tickets, no more flushing. However this meant that we essentially never preemptively flushed. This caused a write performance regression that Nikolay noticed in an unrelated patch that removed the committing of the transaction during btrfs_end_transaction. The behavior that happened pre that patch was btrfs_end_transaction() would see that we were low on space, and it would commit the transaction. This was bad because in this particular case you could end up with thousands and thousands of transactions being committed during the 5 minute reproducer. With the patch to remove this behavior we got much more sane transaction commits, but we ended up slower because we would write for a while, flush, write for a while, flush again. To address this we need to reinstate a preemptive flushing mechanism. However it is distinctly different from our ticketing flushing in that it doesn't have tickets to base it's decisions on. Instead of bolting this logic into our existing flushing work, add another worker to handle this preemptive flushing. Here we will attempt to be slightly intelligent about the things that we flushing, attempting to balance between whichever pool is taking up the most space. Reviewed-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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| Documentation | ||
| LICENSES | ||
| arch | ||
| block | ||
| certs | ||
| crypto | ||
| drivers | ||
| fs | ||
| include | ||
| init | ||
| ipc | ||
| kernel | ||
| lib | ||
| mm | ||
| net | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .cocciconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
| Kconfig | ||
| MAINTAINERS | ||
| Makefile | ||
| README | ||
README
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.