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3ef2268403
Recently, we found that the CPU spent a lot of time in
xfs_alloc_ag_vextent_size when the filesystem has millions of fragmented
spaces.
The reason is that we conducted much extra searching for extents that
could not yield a better result, and these searches would cost a lot of
time when there were millions of extents to search through. Even if we
get the same result length, we don't switch our choice to the new one,
so we can definitely terminate the search early.
Since the result length cannot exceed the found length, when the found
length equals the best result length we already have, we can conclude
the search.
We did a test in that filesystem:
[root@localhost ~]# xfs_db -c freesp /dev/vdb
from to extents blocks pct
1 1 215 215 0.01
2 3 994476 1988952 99.99
Before this patch:
0) | xfs_alloc_ag_vextent_size [xfs]() {
0) * 15597.94 us | }
After this patch:
0) | xfs_alloc_ag_vextent_size [xfs]() {
0) 19.176 us | }
Signed-off-by: Chi Zhiling <chizhiling@kylinos.cn>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Carlos Maiolino <cem@kernel.org>
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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 reStructuredText 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.