Currently flush_dcache_page() thinks pages as non-mapped if
mapping_mapped(mapping) return false. This approach is very
coase:
- mmap on part of file may cause all pages backed on
the file being thought as mmaped
- file-backed pages aren't mapped into user space actually
if the memory mmaped on the file isn't accessed
This patch uses page_mapped() to decide if the page has been
mapped.
From the attached test code, I find there is much performance
improvement(>25%) when accessing page caches via read under this
situations, so memcpy benefits a lot from not flushing cache
under this situation.
No. read time without the patch No. read time with the patch
================================================================
No. 0, time 22615636 us No. 0, time 22014717 us
No. 1, time 4387851 us No. 1, time 3113184 us
No. 2, time 4276535 us No. 2, time 3005244 us
No. 3, time 4259821 us No. 3, time 3001565 us
No. 4, time 4263811 us No. 4, time 3002748 us
No. 5, time 4258486 us No. 5, time 3004104 us
No. 6, time 4253009 us No. 6, time 3002188 us
No. 7, time 4262809 us No. 7, time 2998196 us
No. 8, time 4264525 us No. 8, time 3007255 us
No. 9, time 4267795 us No. 9, time 3005094 us
1), No.0. is to read the file from storage device, and others are
to read the file from page caches basically.
2), file size is 512M, and is on ext4 over usb mass storage.
3), the test is done on Pandaboard.
unsigned int sum = 0;
unsigned long sum_val = 0;
static unsigned long tv_diff(struct timeval *tv1, struct timeval *tv2)
{
return (tv2->tv_sec - tv1->tv_sec) * 1000000 +
(tv2->tv_usec - tv1->tv_usec);
}
int main(int argc, char *argv[])
{
char *mbuf, fbuf;
int fd;
int i;
unsigned long page_size, size;
struct stat stat;
struct timeval t1, t2;
unsigned char *rbuf = malloc(32 * page_size);
if (!rbuf) {
printf(" %sn", "malloc failed");
exit(-1);
}
page_size = getpagesize();
fd = open(argv[1], O_RDWR);
assert(fd >= 0);
fstat(fd, &stat);
size = stat.st_size;
printf("%s: file %s, size %lu, page size %lun",
argv[0],
argv[1], size, page_size);
gettimeofday(&t1, NULL);
mbuf = mmap(NULL, size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
if (!mbuf) {
printf(" %sn", "mmap failed");
exit(-1);
}
for (i = 0 ; i < size ; i += (page_size * 32)) {
int rcnt;
lseek(fd, i, SEEK_SET);
rcnt = read(fd, rbuf, page_size * 32);
if (rcnt != page_size * 32) {
printf("%s: read faildn", __func__);
exit(-1);
}
}
free(rbuf);
munmap(mbuf, size);
gettimeofday(&t2, NULL);
printf("tread mmaped time: %luusn", tv_diff(&t1, &t2));
close(fd);
}
Cc: Michel Lespinasse <walken@google.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Nicolas Pitre <nicolas.pitre@linaro.org>
Reviewed-by: Will Deacon <will.deacon@arm.com>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Ming Lei <ming.lei@canonical.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
81f28946a8