Re: [PATCH v2] mm: expand documentation over __read_mostly
On Thu, May 07, 2020 at 04:14:24PM +, Luis Chamberlain wrote: > __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. > > Acked-by: Christoph Lameter > Signed-off-by: Luis Chamberlain > --- > > This v2 just has a few spelling fixes. > > include/linux/cache.h | 10 -- > 1 file changed, 8 insertions(+), 2 deletions(-) > > diff --git a/include/linux/cache.h b/include/linux/cache.h > index 750621e41d1c..8106fb304fa7 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 > -- > 2.25.1 > Acked-by: Rafael Aquini
Re: [PATCH v2] mm: expand documentation over __read_mostly
On Thu, May 07, 2020 at 04:14:24PM +, Luis Chamberlain wrote: > __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. > > Acked-by: Christoph Lameter > Signed-off-by: Luis Chamberlain Reviewed-by: Kees Cook -- Kees Cook
[PATCH v2] mm: 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. Acked-by: Christoph Lameter Signed-off-by: Luis Chamberlain --- This v2 just has a few spelling fixes. include/linux/cache.h | 10 -- 1 file changed, 8 insertions(+), 2 deletions(-) diff --git a/include/linux/cache.h b/include/linux/cache.h index 750621e41d1c..8106fb304fa7 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 -- 2.25.1
