Re: [RFC] perf tools: Add hugetlbfs memory recognition

Hou Pengyang
2015-06-27T09:08:52Z

On 2015/6/27 16:49, Hou Pengyang wrote:
> Maps for JIT is helpful for symbols-parsing for anon-executable-memory.
> What we need to do is to add (START, SIZE, symbolname) to /tmp/perf-%d.map
> (%d = pid of process), and perf would parse symbol located in this area
> according to /tmp/perf-%d.map. It works well for normal mmap.
>
> However, when we alloc such memory from hugetlbfs by the following code:
>
> ......
>
> fd = open("/mnt/huge/hugepagefile", O_CREAT | O_RDWR, 0755);
> if (fd < 0) {
> perror("Open failed");
> exit(1);
> }
> addr = mmap(ADDR, LENGTH, PROT_READ | PROT_WRITE | \
> PROT_EXEC, MAP_SHARED, fd, 0);
>
> ......
> where hugetlbfs is mounted in /mnt/huge. Symbols could not be parsed correctly:
>
> #perf report
> 86.96% 0.00% hugepage-mmap hugepagefile [.] 0xffffffe00000005c
> 86.96% 0.00% hugepage-mmap hugepagefile [.] 0xffffffe0000000ac
>
> This is because such mmap area's file backed is "/mnt/huge/hugepagefile", a node
> in pseudo filesystem, it is useless for symbol-parsing. so wo had better recognize
> such hugetlbfs area, and rename it's filename to /tmp/perf-%d.map, just as anon-memory
> and no_dso_memory do.
>
> This patch imports a new function named is_hugetlb_memory to check if this memory
> is from hugetlbfs. If true, change its name.
>
> After this patch:
> #perf report
> 86.96% 0.00% hugepage-mmap perf-182.map [.] 0x000000200000005c
> 86.96% 0.00% hugepage-mmap perf-182.map [.] 0x00000020000000ac
>
> We can add maps info to perf-182.map for further symbols-parsing.
>
> Signed-off-by: Hou Pengyang <houpengyang@huawei.com>
> ---
> tools/perf/util/map.c | 11 +++++++++--
> 1 file changed, 9 insertions(+), 2 deletions(-)
>
> diff --git a/tools/perf/util/map.c b/tools/perf/util/map.c
> index b5a5e9c..796db08 100644
> --- a/tools/perf/util/map.c
> +++ b/tools/perf/util/map.c
> @@ -15,6 +15,7 @@
> #include "debug.h"
> #include "machine.h"
> #include <linux/string.h>
> +#include <sys/mman.h>
>
> static void __maps__insert(struct maps *maps, struct map *map);
>
> @@ -43,6 +44,11 @@ static inline int is_android_lib(const char *filename)
> !strncmp(filename, "/system/lib", 11);
> }
>
> +static inline int is_hugetlb_memory(u32 flags)
> +{
> + return flags & MAP_HUGETLB;
> +}

There is something about MAP_HUGETLB.

In this patch, we check if a mmap area is hugetlbfs area by MAP_HUGETLB,
a bit in MMAP2 event.

However, if mmap area is hugetlb related, MAP_HUGETLB does not always
appear. Because, there are two ways generating MMAP2 event.

1) when a new vm_area_struct is created, its info would be exported
as a MMAP2 event.
2) perf reads /proc/pid/maps for generating MMAP2 event.

MAP_HUGETLB appears if MMAP2 event is generated on situation 1),
while not on situation 2).

This is because on situation 2), perf reads /proc/pid/maps, which
contains only PROT_READ/WRITE/EXEC, MAP_SHARED/MAP_PRIVATE, while more
details appear in /proc/pid/smaps, such as MAP_HUGETLB.

So I wonder if there is a need to read /proc/pid/smaps instead of
/proc/pid/maps to generate MMAP2 event. Or we should solve the problem
by another way?

Thanks!

> +
> static inline bool replace_android_lib(const char *filename, char *newfilename)
> {
> const char *libname;
> @@ -151,12 +157,13 @@ struct map *map__new(struct machine *machine, u64 start, u64 len,
> if (map != NULL) {
> char newfilename[PATH_MAX];
> struct dso *dso;
> - int anon, no_dso, vdso, android;
> + int anon, no_dso, vdso, android, hugetlb;
>
> android = is_android_lib(filename);
> anon = is_anon_memory(filename);
> vdso = is_vdso_map(filename);
> no_dso = is_no_dso_memory(filename);
> + hugetlb = is_hugetlb_memory(flags);
>
> map->maj = d_maj;
> map->min = d_min;
> @@ -165,7 +172,7 @@ struct map *map__new(struct machine *machine, u64 start, u64 len,
> map->prot = prot;
> map->flags = flags;
>
> - if ((anon || no_dso) && type == MAP__FUNCTION) {
> + if ((anon || no_dso || hugetlb) && type == MAP__FUNCTION) {
> snprintf(newfilename, sizeof(newfilename), "/tmp/perf-%d.map", pid);
> filename = newfilename;
> }
>