From 81f28946a8b066d484ca8935ff545d94ce730aa3 Mon Sep 17 00:00:00 2001 From: Ming Lei Date: Wed, 5 Jun 2013 02:44:00 +0100 Subject: [PATCH] ARM: 7746/1: mm: lazy cache flushing on non-mapped pages 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 Cc: Andrew Morton Cc: Nicolas Pitre Reviewed-by: Will Deacon Acked-by: Catalin Marinas Signed-off-by: Ming Lei Signed-off-by: Russell King --- arch/arm/mm/flush.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/arch/arm/mm/flush.c b/arch/arm/mm/flush.c index 0d473cce501c..2ff66eb98ff0 100644 --- a/arch/arm/mm/flush.c +++ b/arch/arm/mm/flush.c @@ -287,7 +287,7 @@ void flush_dcache_page(struct page *page) mapping = page_mapping(page); if (!cache_ops_need_broadcast() && - mapping && !mapping_mapped(mapping)) + mapping && !page_mapped(page)) clear_bit(PG_dcache_clean, &page->flags); else { __flush_dcache_page(mapping, page); -- 2.20.1