On Tue, Dec 22, 2020 at 5:49 PM <qianjun.kernel@xxxxxxxxx> wrote: > > 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 you have time diff for both parent and child process ? > 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 > >