1. Patchew
  2. linux
  3. [PATCH v3 00/50] Improvements to memory use
  4. View patch

[PATCH v3 13/50] libperf: Lazily allocate mmap event copy

Ian Rogers posted 50 patches 2 years, 2 months ago
There is a newer version of this series
[PATCH v3 13/50] libperf: Lazily allocate mmap event copy
Posted by Ian Rogers 2 years, 2 months ago 
The event copy in the mmap is used to have storage to a read
event. Not all users of mmaps read the events, such as perf record, so
switch the allocation to being on first read rather than being
embedded within the perf_mmap.

Signed-off-by: Ian Rogers <irogers@google.com>
---
 tools/lib/perf/include/internal/mmap.h | 2 +-
 tools/lib/perf/mmap.c                  | 9 +++++++++
 2 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/tools/lib/perf/include/internal/mmap.h b/tools/lib/perf/include/internal/mmap.h
index 5a062af8e9d8..b11aaf5ed645 100644
--- a/tools/lib/perf/include/internal/mmap.h
+++ b/tools/lib/perf/include/internal/mmap.h
@@ -33,7 +33,7 @@ struct perf_mmap {
 	bool			 overwrite;
 	u64			 flush;
 	libperf_unmap_cb_t	 unmap_cb;
-	char			 event_copy[PERF_SAMPLE_MAX_SIZE] __aligned(8);
+	void			*event_copy;
 	struct perf_mmap	*next;
 };
 
diff --git a/tools/lib/perf/mmap.c b/tools/lib/perf/mmap.c
index 2184814b37dd..91ae46aac378 100644
--- a/tools/lib/perf/mmap.c
+++ b/tools/lib/perf/mmap.c
@@ -51,6 +51,8 @@ int perf_mmap__mmap(struct perf_mmap *map, struct perf_mmap_param *mp,
 
 void perf_mmap__munmap(struct perf_mmap *map)
 {
+	free(map->event_copy);
+	map->event_copy = NULL;
 	if (map && map->base != NULL) {
 		munmap(map->base, perf_mmap__mmap_len(map));
 		map->base = NULL;
@@ -226,6 +228,13 @@ static union perf_event *perf_mmap__read(struct perf_mmap *map,
 			unsigned int len = min(sizeof(*event), size), cpy;
 			void *dst = map->event_copy;
 
+			if (!dst) {
+				dst = malloc(PERF_SAMPLE_MAX_SIZE);
+				if (!dst)
+					return NULL;
+				map->event_copy = dst;
+			}
+
 			do {
 				cpy = min(map->mask + 1 - (offset & map->mask), len);
 				memcpy(dst, &data[offset & map->mask], cpy);
-- 
2.42.0.758.gaed0368e0e-goog
Re: [PATCH v3 13/50] libperf: Lazily allocate mmap event copy
Posted by Yang Jihong 2 years, 2 months ago 
Hello,

On 2023/10/25 6:23, Ian Rogers wrote:
> The event copy in the mmap is used to have storage to a read
> event. Not all users of mmaps read the events, such as perf record, so
> switch the allocation to being on first read rather than being
> embedded within the perf_mmap.
> 
> Signed-off-by: Ian Rogers <irogers@google.com>
> ---
>   tools/lib/perf/include/internal/mmap.h | 2 +-
>   tools/lib/perf/mmap.c                  | 9 +++++++++
>   2 files changed, 10 insertions(+), 1 deletion(-)
> 
> diff --git a/tools/lib/perf/include/internal/mmap.h b/tools/lib/perf/include/internal/mmap.h
> index 5a062af8e9d8..b11aaf5ed645 100644
> --- a/tools/lib/perf/include/internal/mmap.h
> +++ b/tools/lib/perf/include/internal/mmap.h
> @@ -33,7 +33,7 @@ struct perf_mmap {
>   	bool			 overwrite;
>   	u64			 flush;
>   	libperf_unmap_cb_t	 unmap_cb;
> -	char			 event_copy[PERF_SAMPLE_MAX_SIZE] __aligned(8);
> +	void			*event_copy;
>   	struct perf_mmap	*next;
>   };
>   
> diff --git a/tools/lib/perf/mmap.c b/tools/lib/perf/mmap.c
> index 2184814b37dd..91ae46aac378 100644
> --- a/tools/lib/perf/mmap.c
> +++ b/tools/lib/perf/mmap.c
> @@ -51,6 +51,8 @@ int perf_mmap__mmap(struct perf_mmap *map, struct perf_mmap_param *mp,
>   
>   void perf_mmap__munmap(struct perf_mmap *map)
>   {
> +	free(map->event_copy);
> +	map->event_copy = NULL;
>   	if (map && map->base != NULL) {
>   		munmap(map->base, perf_mmap__mmap_len(map));
>   		map->base = NULL;
> @@ -226,6 +228,13 @@ static union perf_event *perf_mmap__read(struct perf_mmap *map,
>   			unsigned int len = min(sizeof(*event), size), cpy;
>   			void *dst = map->event_copy;
>   
> +			if (!dst) {
> +				dst = malloc(PERF_SAMPLE_MAX_SIZE);
`event` is used as the return parameter of libperf API 
perf_mmap__read_event().
Is `zalloc` better to avoid dirty data?

Thanks,
Yang
Re: [PATCH v3 13/50] libperf: Lazily allocate mmap event copy
Posted by Ian Rogers 2 years, 2 months ago 
On Tue, Oct 24, 2023 at 7:39 PM Yang Jihong <yangjihong1@huawei.com> wrote:
>
> Hello,
>
> On 2023/10/25 6:23, Ian Rogers wrote:
> > The event copy in the mmap is used to have storage to a read
> > event. Not all users of mmaps read the events, such as perf record, so
> > switch the allocation to being on first read rather than being
> > embedded within the perf_mmap.
> >
> > Signed-off-by: Ian Rogers <irogers@google.com>
> > ---
> >   tools/lib/perf/include/internal/mmap.h | 2 +-
> >   tools/lib/perf/mmap.c                  | 9 +++++++++
> >   2 files changed, 10 insertions(+), 1 deletion(-)
> >
> > diff --git a/tools/lib/perf/include/internal/mmap.h b/tools/lib/perf/include/internal/mmap.h
> > index 5a062af8e9d8..b11aaf5ed645 100644
> > --- a/tools/lib/perf/include/internal/mmap.h
> > +++ b/tools/lib/perf/include/internal/mmap.h
> > @@ -33,7 +33,7 @@ struct perf_mmap {
> >       bool                     overwrite;
> >       u64                      flush;
> >       libperf_unmap_cb_t       unmap_cb;
> > -     char                     event_copy[PERF_SAMPLE_MAX_SIZE] __aligned(8);
> > +     void                    *event_copy;
> >       struct perf_mmap        *next;
> >   };
> >
> > diff --git a/tools/lib/perf/mmap.c b/tools/lib/perf/mmap.c
> > index 2184814b37dd..91ae46aac378 100644
> > --- a/tools/lib/perf/mmap.c
> > +++ b/tools/lib/perf/mmap.c
> > @@ -51,6 +51,8 @@ int perf_mmap__mmap(struct perf_mmap *map, struct perf_mmap_param *mp,
> >
> >   void perf_mmap__munmap(struct perf_mmap *map)
> >   {
> > +     free(map->event_copy);
> > +     map->event_copy = NULL;
> >       if (map && map->base != NULL) {
> >               munmap(map->base, perf_mmap__mmap_len(map));
> >               map->base = NULL;
> > @@ -226,6 +228,13 @@ static union perf_event *perf_mmap__read(struct perf_mmap *map,
> >                       unsigned int len = min(sizeof(*event), size), cpy;
> >                       void *dst = map->event_copy;
> >
> > +                     if (!dst) {
> > +                             dst = malloc(PERF_SAMPLE_MAX_SIZE);
> `event` is used as the return parameter of libperf API
> perf_mmap__read_event().
> Is `zalloc` better to avoid dirty data?

We could but I'd prefer not to zero unnecessarily. We've had similar
uninitialized memory being copied to perf.data file problems such as:
http://lore.kernel.org/lkml/20210309234945.419254-1-irogers@google.com
With the sanitizers help we can avoid the problem and do less work,
which I think is best.

Thanks,
Ian

> Thanks,
> Yang

Patchew 2.1-devel-b67e4c2

© 2016 - 2026 Red Hat, Inc.