diff options
| author | Luis Chamberlain <mcgrof@kernel.org> | 2020-06-08 21:35:07 -0700 |
|---|---|---|
| committer | Linus Torvalds <torvalds@linux-foundation.org> | 2020-06-09 09:39:16 -0700 |
| commit | 4fa7252338a56fbc90220e6330f136a379175a7a (patch) | |
| tree | 5061c6346a7723a4970f8d49f13dbf10fcb0087d /include/linux/cache.h | |
| parent | 2a71e81d32198785387c8bc0f2cc5d78f84e2e78 (diff) | |
include/linux/cache.h: expand documentation over __read_mostly
__read_mostly can easily be misused by folks, its not meant for just
read-only data. There are performance reasons for using it, but we also
don't provide any guidance about its use. Provide a bit more guidance
over its use.
Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Acked-by: Christoph Lameter <cl@linux.com>
Acked-by: Rafael Aquini <aquini@redhat.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Matthew Wilcox <willy@infradead.org>
Link: http://lkml.kernel.org/r/20200507161424.2584-1-mcgrof@kernel.org
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'include/linux/cache.h')
| -rw-r--r-- | include/linux/cache.h | 10 |
1 files changed, 8 insertions, 2 deletions
diff --git a/include/linux/cache.h b/include/linux/cache.h index 750621e41d1c..1aa8009f6d06 100644 --- a/include/linux/cache.h +++ b/include/linux/cache.h @@ -15,8 +15,14 @@ /* * __read_mostly is used to keep rarely changing variables out of frequently - * updated cachelines. If an architecture doesn't support it, ignore the - * hint. + * updated cachelines. Its use should be reserved for data that is used + * frequently in hot paths. Performance traces can help decide when to use + * this. You want __read_mostly data to be tightly packed, so that in the + * best case multiple frequently read variables for a hot path will be next + * to each other in order to reduce the number of cachelines needed to + * execute a critical path. We should be mindful and selective of its use. + * ie: if you're going to use it please supply a *good* justification in your + * commit log */ #ifndef __read_mostly #define __read_mostly |