linux-kernel - [PATCH v3 0/8] kallsyms: Optimizes the performance of lookup symbols

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Date:   Mon, 19 Sep 2022 23:15:25 +0800
From:   Zhen Lei <thunder.leizhen@...wei.com>
To:     Josh Poimboeuf <jpoimboe@...nel.org>,
        Jiri Kosina <jikos@...nel.org>,
        Miroslav Benes <mbenes@...e.cz>,
        Petr Mladek <pmladek@...e.com>,
        Joe Lawrence <joe.lawrence@...hat.com>,
        <live-patching@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        Masahiro Yamada <masahiroy@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Jiri Olsa <jolsa@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Luis Chamberlain" <mcgrof@...nel.org>,
        <linux-modules@...r.kernel.org>
CC:     Zhen Lei <thunder.leizhen@...wei.com>
Subject: [PATCH v3 0/8] kallsyms: Optimizes the performance of lookup symbols

v2 --> v3:
1. Improve test cases, perform complete functional tests on functions
   kallsyms_lookup_name(), kallsyms_on_each_symbol() and
   kallsyms_on_each_match_symbol().
2. Add patch [PATCH v3 2/8] scripts/kallsyms: ensure that all possible
   combinations are compressed.
3. The symbol type is not compressed regardless of whether
   CONFIG_KALLSYMS_ALL is set or not. The memory overhead is increased
   by less than 20KiB if CONFIG_KALLSYMS_ALL=n.
4. Discard [PATCH v2 3/8] kallsyms: Adjust the types of some local variables

v1 --> v2:
Add self-test facility

v1:
Currently, to search for a symbol, we need to expand the symbols in
'kallsyms_names' one by one, and then use the expanded string for
comparison. This is very slow.

In fact, we can first compress the name being looked up and then use
it for comparison when traversing 'kallsyms_names'.

This patch series optimizes the performance of function kallsyms_lookup_name(),
and function klp_find_object_symbol() in the livepatch module. Based on the
test results, the performance overhead is reduced to 5%. That is, the
performance of these functions is improved by 20 times.

To avoid increasing the kernel size in non-debug mode, the optimization is only
for the case CONFIG_KALLSYMS_ALL=y.

Zhen Lei (8):
  scripts/kallsyms: rename build_initial_tok_table()
  scripts/kallsyms: ensure that all possible combinations are compressed
  scripts/kallsyms: don't compress symbol types
  kallsyms: Improve the performance of kallsyms_lookup_name()
  kallsyms: Add helper kallsyms_on_each_match_symbol()
  livepatch: Use kallsyms_on_each_match_symbol() to improve performance
  livepatch: Improve the search performance of
    module_kallsyms_on_each_symbol()
  kallsyms: Add self-test facility

 include/linux/kallsyms.h   |   8 +
 init/Kconfig               |  13 ++
 kernel/Makefile            |   1 +
 kernel/kallsyms.c          | 106 +++++++++-
 kernel/kallsyms_selftest.c | 424 +++++++++++++++++++++++++++++++++++++
 kernel/livepatch/core.c    |  25 ++-
 kernel/module/kallsyms.c   |  13 +-
 scripts/kallsyms.c         |  24 ++-
 8 files changed, 598 insertions(+), 16 deletions(-)
 create mode 100644 kernel/kallsyms_selftest.c

-- 
2.25.1