8847ecc927
DRC bucket pruning is done by nfsd_cache_lookup(), which is part of every NFSv2 and NFSv3 dispatch (ie, it's done while the client is waiting). I added a trace_printk() in prune_bucket() to see just how long it takes to prune. Here are two ends of the spectrum: prune_bucket: Scanned 1 and freed 0 in 90 ns, 62 entries remaining prune_bucket: Scanned 2 and freed 1 in 716 ns, 63 entries remaining ... prune_bucket: Scanned 75 and freed 74 in 34149 ns, 1 entries remaining Pruning latency is noticeable on fast transports with fast storage. By noticeable, I mean that the latency measured here in the worst case is the same order of magnitude as the round trip time for cached server operations. We could do something like moving expired entries to an expired list and then free them later instead of freeing them right in prune_bucket(). But simply limiting the number of entries that can be pruned by a lookup is simple and retains more entries in the cache, making the DRC somewhat more effective. Comparison with a 70/30 fio 8KB 12 thread direct I/O test: Before: write: IOPS=61.6k, BW=481MiB/s (505MB/s)(14.1GiB/30001msec); 0 zone resets WRITE: 1848726 ops (30%) avg bytes sent per op: 8340 avg bytes received per op: 136 backlog wait: 0.635158 RTT: 0.128525 total execute time: 0.827242 (milliseconds) After: write: IOPS=63.0k, BW=492MiB/s (516MB/s)(14.4GiB/30001msec); 0 zone resets WRITE: 1891144 ops (30%) avg bytes sent per op: 8340 avg bytes received per op: 136 backlog wait: 0.616114 RTT: 0.126842 total execute time: 0.805348 (milliseconds) Signed-off-by: Chuck Lever <chuck.lever@oracle.com> Signed-off-by: J. Bruce Fields <bfields@redhat.com> |
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| 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.