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Subject[PATCH 3/2] perf: Optimize the fill/align code in perf_event_mmap_event()
1. memset(tmp, 0) and especially kzalloc(PATH_MAX) are suboptimal,
we only need to zero-fill the alignment.

Remove this memset/__GFP_ZERO and fill the extra bytes by hand.

2. The usage of strncpy(tmp) is not optimal too, we can add the new
label and do this in one place.

Signed-off-by: Oleg Nesterov <oleg@redhat.com>
---
kernel/events/core.c | 47 +++++++++++++++++++++++------------------------
1 files changed, 23 insertions(+), 24 deletions(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 4a1e7b8..777a268 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -5098,20 +5098,17 @@ static void perf_event_mmap_event(struct perf_mmap_event *mmap_event)
int maj = 0, min = 0;
u64 ino = 0, gen = 0;
unsigned int size;
- char tmp[16];
- char *buf = NULL;
- const char *name;
-
- memset(tmp, 0, sizeof(tmp));
+ char tmp[16], *name, *buf = NULL;
+ const char *str;

if (file) {
struct inode *inode;
dev_t dev;

- buf = kzalloc(PATH_MAX, GFP_KERNEL);
+ buf = kmalloc(PATH_MAX, GFP_KERNEL);
if (!buf) {
- name = strncpy(tmp, "//enomem", sizeof(tmp));
- goto got_name;
+ str = "//enomem";
+ goto cpy_name;
}
/*
* d_path works from the end of the rb backwards, so we
@@ -5120,8 +5117,8 @@ static void perf_event_mmap_event(struct perf_mmap_event *mmap_event)
*/
name = d_path(&file->f_path, buf, PATH_MAX - sizeof(u64));
if (IS_ERR(name)) {
- name = strncpy(tmp, "//toolong", sizeof(tmp));
- goto got_name;
+ str = "//toolong";
+ goto cpy_name;
}
inode = file_inode(vma->vm_file);
dev = inode->i_sb->s_dev;
@@ -5129,32 +5126,34 @@ static void perf_event_mmap_event(struct perf_mmap_event *mmap_event)
gen = inode->i_generation;
maj = MAJOR(dev);
min = MINOR(dev);
-
+ goto got_name;
} else {
- name = arch_vma_name(vma);
- if (name) {
- name = strncpy(tmp, name, sizeof(tmp) - 1);
- tmp[sizeof(tmp) - 1] = '\0';
- goto got_name;
- }
+ str = arch_vma_name(vma);
+ if (str)
+ goto cpy_name;

if (vma->vm_start <= vma->vm_mm->start_brk &&
vma->vm_end >= vma->vm_mm->brk) {
- name = strncpy(tmp, "[heap]", sizeof(tmp));
- goto got_name;
+ str = "[heap]";
+ goto cpy_name;
}
if (vma->vm_start <= vma->vm_mm->start_stack &&
vma->vm_end >= vma->vm_mm->start_stack) {
- name = strncpy(tmp, "[stack]", sizeof(tmp));
- goto got_name;
+ str = "[stack]";
+ goto cpy_name;
}

- name = strncpy(tmp, "//anon", sizeof(tmp));
- goto got_name;
+ str = "//anon";
+ goto cpy_name;
}

+cpy_name:
+ strlcpy(tmp, str, sizeof(tmp));
+ name = tmp;
got_name:
- size = ALIGN(strlen(name)+1, sizeof(u64));
+ size = strlen(name) + 1;
+ while (size % sizeof(u64))
+ name[size++] = '\0';

mmap_event->file_name = name;
mmap_event->file_size = size;
--
1.5.5.1



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