Re: [f2fs-dev] [PATCH] f2fs_io: add fragread command to evaluate fragmented buffer for reads

[Jaegeuk Kim via Linux-f2fs-devel <linux-f2fs-devel@lists.sourceforge.net>]

On 03/11, Chao Yu wrote:
> On 3/4/25 09:10, Jaegeuk Kim via Linux-f2fs-devel wrote:
> > From: Jaegeuk Kim <jaegeuk@google.com>
> > 
> > This adds a fragread command in f2fs_io, which is able to measure the
> > read performance on fragmented data buffer.
> > 
> > Signed-off-by: Jaegeuk Kim <jaegeuk@google.com>
> > ---
> >  tools/f2fs_io/f2fs_io.c | 110 ++++++++++++++++++++++++++++++++++++++++
> >  1 file changed, 110 insertions(+)
> > 
> > diff --git a/tools/f2fs_io/f2fs_io.c b/tools/f2fs_io/f2fs_io.c
> > index b72c26648f56..8431262575e0 100644
> > --- a/tools/f2fs_io/f2fs_io.c
> > +++ b/tools/f2fs_io/f2fs_io.c
> > @@ -1018,6 +1018,115 @@ static void do_read(int argc, char **argv, const struct cmd_desc *cmd)
> >  	exit(0);
> >  }
> >  
> > +#define fragread_desc "read data with a fragmented buffer from file"
> > +#define fragread_help					\
> > +"f2fs_io fragread [chunk_size in 4kb] [offset in chunk_size] [count] [advice] [file_path]\n\n"	\
> > +"Read data in file_path and print nbytes\n"		\
> > +"advice can be\n"					\
> > +" 1 : set sequential|willneed\n"			\
> > +" 0 : none\n"						\
> > +
> > +#ifndef PAGE_SIZE
> > +#define PAGE_SIZE sysconf(_SC_PAGESIZE)
> > +#endif
> > +#define ALLOC_SIZE (2 * 1024 * 1024 - 4 * 1024) // 2MB - 4KB
> > +
> > +static void do_fragread(int argc, char **argv, const struct cmd_desc *cmd)
> > +{
> > +	u64 buf_size = 0, ret = 0, read_cnt = 0;
> > +	u64 offset;
> > +	char *buf = NULL;
> > +	uintptr_t idx, ptr;
> > +	unsigned bs, count, i;
> > +	u64 total_time = 0;
> > +	int flags = 0, alloc_count = 0;
> > +	void *mem_hole, **mem_holes;
> > +	int fd, advice;
> > +
> > +	if (argc != 6) {
> > +		fputs("Excess arguments\n\n", stderr);
> > +		fputs(cmd->cmd_help, stderr);
> > +		exit(1);
> > +	}
> > +
> > +	bs = atoi(argv[1]);
> > +	if (bs > 256 * 1024)
> > +		die("Too big chunk size - limit: 1GB");
> > +	buf_size = bs * F2FS_DEFAULT_BLKSIZE;
> > +
> > +	offset = atoi(argv[2]) * buf_size;
> > +	count = atoi(argv[3]);
> > +	advice = atoi(argv[4]);
> > +	mem_holes = xmalloc(sizeof(void *) * (buf_size / PAGE_SIZE));
> > +
> > +	/* 1. Allocate the buffer using mmap. */
> > +	buf = mmap(NULL, buf_size, PROT_READ | PROT_WRITE,
> > +				MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
> > +
> > +	/* 2. Loop and touch each page. */
> > +	for (idx = (uintptr_t)buf; idx < (uintptr_t)buf + buf_size;
> > +						idx += PAGE_SIZE)
> > +	{
> > +		/* Touch the current page. */
> > +		volatile char *page = (volatile char *)idx;
> > +		*page;
> > +
> > +		/* 3. Allocate (2M - 4K) memory using mmap and touch all of it. */
> > +		mem_hole = mmap(NULL, ALLOC_SIZE, PROT_READ | PROT_WRITE,
> > +					MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
> > +		if (mem_hole == MAP_FAILED)
> > +			die_errno("map failed");
> > +
> > +		/* Store the allocated memory pointer. */
> > +		mem_holes[alloc_count++] = mem_hole;
> 
> Do we need to call mlock to hold allocated cache in the memory, if
> administrator enables swap, memory fragment will be gone once anonymous
> pages are swapped to device?

Hmm, the test is going to use this very intensively, so is it possible?

> 
> Thanks,
> 
> > +
> > +		/* Touch all allocated memory. */
> > +		for (ptr = (uintptr_t)mem_hole;
> > +			ptr < (uintptr_t)mem_hole + ALLOC_SIZE;
> > +						ptr += PAGE_SIZE) {
> > +			volatile char *alloc_page = (volatile char *)ptr;
> > +			*alloc_page;
> > +		}
> > +	}
> > +	printf("Touched allocated memory: count = %u\n", alloc_count);
> > +	printf(" - allocated memory: = ");
> > +	for (idx = 0; idx < 5; idx++)
> > +		printf(" %p", mem_holes[idx]);
> > +	printf("\n");
> > +
> > +	fd = xopen(argv[5], O_RDONLY | flags, 0);
> > +
> > +	if (advice) {
> > +		if (posix_fadvise(fd, 0, F2FS_DEFAULT_BLKSIZE,
> > +				POSIX_FADV_SEQUENTIAL) != 0)
> > +			die_errno("fadvise failed");
> > +		if (posix_fadvise(fd, 0, F2FS_DEFAULT_BLKSIZE,
> > +				POSIX_FADV_WILLNEED) != 0)
> > +			die_errno("fadvise failed");
> > +		printf("fadvise SEQUENTIAL|WILLNEED to a file: %s\n", argv[5]);
> > +	}
> > +
> > +	total_time = get_current_us();
> > +
> > +	for (i = 0; i < count; i++) {
> > +		ret = pread(fd, buf, buf_size, offset + buf_size * i);
> > +		if (ret != buf_size) {
> > +			printf("pread expected: %"PRIu64", readed: %"PRIu64"\n",
> > +					buf_size, ret);
> > +			if (ret > 0)
> > +				read_cnt += ret;
> > +			break;
> > +		}
> > +
> > +		read_cnt += ret;
> > +	}
> > +	printf("Fragmented_Read %"PRIu64" bytes total_time = %"PRIu64" us, BW = %.Lf MB/s\n",
> > +		read_cnt, get_current_us() - total_time,
> > +		((long double)read_cnt / (get_current_us() - total_time)));
> > +	printf("\n");
> > +	exit(0);
> > +}
> > +
> >  #define randread_desc "random read data from file"
> >  #define randread_help					\
> >  "f2fs_io randread [chunk_size in 4kb] [count] [IO] [advise] [file_path]\n\n"	\
> > @@ -2002,6 +2111,7 @@ const struct cmd_desc cmd_list[] = {
> >  	CMD(write_advice),
> >  	CMD(read),
> >  	CMD(randread),
> > +	CMD(fragread),
> >  	CMD(fiemap),
> >  	CMD(gc_urgent),
> >  	CMD(defrag_file),


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