mainlining shenanigans
5fc475b749
Rasmus Villemoes points out that the 'in_group_p()' tests can be a noticeable expense, and often completely unnecessary. A common situation is that the 'group' bits are the same as the 'other' bits wrt the permissions we want to test. So rewrite 'acl_permission_check()' to not bother checking for group ownership when the permission check doesn't care. For example, if we're asking for read permissions, and both 'group' and 'other' allow reading, there's really no reason to check if we're part of the group or not: either way, we'll allow it. Rasmus says: "On a bog-standard Ubuntu 20.04 install, a workload consisting of compiling lots of userspace programs (i.e., calling lots of short-lived programs that all need to get their shared libs mapped in, and the compilers poking around looking for system headers - lots of /usr/lib, /usr/bin, /usr/include/ accesses) puts in_group_p around 0.1% according to perf top. System-installed files are almost always 0755 (directories and binaries) or 0644, so in most cases, we can avoid the binary search and the cost of pulling the cred->groups array and in_group_p() .text into the cpu cache" Reported-by: Rasmus Villemoes <linux@rasmusvillemoes.dk> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> |
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| arch | ||
| block | ||
| certs | ||
| crypto | ||
| Documentation | ||
| drivers | ||
| fs | ||
| include | ||
| init | ||
| ipc | ||
| kernel | ||
| lib | ||
| LICENSES | ||
| 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 | ||
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.