From: jun qian <qianjun.kernel@xxxxxxxxx>
In our project, Many business delays come from fork, so
we started looking for the reason why fork is time-consuming.
I used the ftrace with function_graph to trace the fork, found
that the vm_normal_page will be called tens of thousands and
the execution time of this vm_normal_page function is only a
few nanoseconds. And the vm_normal_page is not a inline function.
So I think if the function is inline style, it maybe reduce the
call time overhead.
I did the following experiment:
I have wrote the c test code, pls ignore the memory leak :)
Before fork, I will malloc 4G bytes, then acculate the fork
time.
int main()
{
char *p;
unsigned long long i=0;
float time_use=0;
struct timeval start;
struct timeval end;
for(i=0; i<LEN; i++) {
p = (char *)malloc(4096);
if (p == NULL) {
printf("malloc failed!\n");
return 0;
}
p[0] = 0x55;
}
gettimeofday(&start,NULL);
fork();
gettimeofday(&end,NULL);
time_use=(end.tv_sec * 1000000 + end.tv_usec) -
(start.tv_sec * 1000000 + start.tv_usec);
printf("time_use is %.10f us\n",time_use);
return 0;
}
We need to compare the changes in the size of vmlinux, the time of
fork in inline and non-inline cases, and the vm_normal_page will be
called in many function. So we also need to compare this function's
size. For examples, the do_wp_page will call vm_normal_page, so I
also calculated it's size.
inline non-inline diff
vmlinux size 9709248 bytes 9709824 bytes -576 bytes
fork time 23475ns 24638ns -4.7%
do_wp_page size 972 743 +229
According to the above test data, I think inline vm_normal_page can
reduce fork execution time.
Signed-off-by: jun qian <qianjun.kernel@xxxxxxxxx>
---
mm/memory.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/mm/memory.c b/mm/memory.c
index 7d608765932b..a689bb5d3842 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -591,7 +591,7 @@ static void print_bad_pte(struct vm_area_struct *vma, unsigned long addr,
* PFNMAP mappings in order to support COWable mappings.
*
*/
-struct page *vm_normal_page(struct vm_area_struct *vma, unsigned long addr,
+inline struct page *vm_normal_page(struct vm_area_struct *vma, unsigned long addr,
pte_t pte)
{
unsigned long pfn = pte_pfn(pte);
--
2.18.2
