Re: [PATCH V8 0/2] mm: shmem: support POSIX_FADV_[WILL|DONT]NEED for shmem files

[Charan Teja Kalla <quic_charante@quicinc.com>]

Just a ping to have your valuable inputs here.

On 4/28/2023 8:32 PM, Charan Teja Kalla wrote:
> This patch aims to implement POSIX_FADV_WILLNEED and POSIX_FADV_DONTNEED
> advices to shmem files which can be helpful for the drivers who may want
> to manage the pages of shmem files on their own, like, that are created
> through shmem_file_setup[_with_mnt]().
> 
> This patchset is unit tested with the below:
> (a) Qemu x86_64 with 4 smp cores, 2GB ram, 1Gb swap mounted
>     on zram block device.
> (b) A tmpfs file of size 100MB is created.
> (c) Initially this file is filled with a poison value of 0xAA. 
> (d) POSIX_FADV_[WILL|DONT]NEED is called on this file for a range that
>     gets generated randomn. This is called for 10K iterations.
> (e) Check the poison value at the end of the test. Exit the program if it
>     is changed.
> 
> use the below script:
> val1=$(cat /proc/vmstat | grep pswpout | awk '{print $2}')
> str=$(./a.out <tmpfs file>)
> res=$(echo $str | awk '{print $1}')
> val2=$(cat /proc/vmstat | grep pswpout | awk '{print $2}')
> 
> if [[ $res == "FAIL" ]]; then echo $str;
> else
> 	if [[ $val1 == $val2 ]]; then echo "FAIL. Does the swap setup is done?"; 
>         else echo $res;
>         fi
> fi
> ------------------------------------------------------------------------
> #include <stdio.h>
> #include <fcntl.h>
> #include <unistd.h>
> #include <stdlib.h>
> #include <string.h>
> #include <sys/mman.h>
> #include <sys/types.h>
> #include <sys/stat.h>
> #include <unistd.h>
> #include <fcntl.h>
> #include <sys/stat.h>
> 
> #define NR_ITER   (10000)
> unsigned int fd;
> 
> void run_tests(int fd, loff_t start, loff_t end)
> {
> 
> 	if (posix_fadvise(fd, start, end, POSIX_FADV_DONTNEED)) {
> 		perror("FAIL : fadvise():dont_need_thread\n");
> 		exit(6);
> 	}
> 
> 	if (posix_fadvise(fd, start, end, POSIX_FADV_WILLNEED)) {
> 		perror("FAIL : fadvise():will_need_thread\n");
> 		exit(6);
> 	}
> }
> 
> void get_rand_range(long size, loff_t *start, loff_t *end)
> {
> 	*start = rand() % (size >> 1);
> 	*end = *start + (rand() % size);
> 
> 	if (*end > size)
> 		*start = *end = 0;
> }
> 
> void fill_pattern(int fd, long size)
> {
> 	char *data;
> 
> 	data = mmap(0, size, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
> 	if (data == MAP_FAILED) {
> 		perror("FAIL : mmap()\n");
> 		exit(5);
> 	}
> 	memset(data, 0xAA, size);
> 	munmap(data, size);
> }
> 
> int check_pattern(int fd, long size)
> {
> 	unsigned char *data;
> 	long i;
> 
> 	data = mmap(0, size, PROT_READ, MAP_SHARED, fd, 0);
> 	if (data == MAP_FAILED) {
> 		perror("FAIL : mmap()\n");
> 		exit(4);
> 	}
> 
> 	for (i = 0; i < size; ++i) {
> 		if (data[i] != 0xAA) {
> 			printf("FAIL : Testcase is failed. Seeing %x rather than 0xAA\n", data[i]);
> 			exit(4);
> 		}
> 	}
> 	munmap(data, size);
> }
> 
> int main(int argc, char **argv)
> {
> 	struct stat buf = {0};
> 	loff_t start, end, i;
> 
> 	if (argc < 2) { 
> 		printf("FAIL : usage: a.out <tmpfs filename>\n");
> 		exit(1);
> 	}
> 
> 
> 	if (stat(argv[1], &buf)) {
> 		perror("FAIL : stat()\n");
> 		exit(2);
> 	}
> 
> 	fd = open(argv[1], O_RDWR);
> 	if (fd < 0) {
> 		perror("FAIL : open()\n");
> 		exit(3);
> 	}
> 
> 	fill_pattern(fd, buf.st_size);
> 	for (i = NR_ITER; i > 0; --i) {
> 		get_rand_range(buf.st_size, &start, &end);
> 		run_tests(fd, start, end);
> 	}
> 	check_pattern(fd, buf.st_size);
> 	
> 	close(fd);
> 
> 	printf("PASS \n");
> 
> 	return 0;
> }
> ------------------------------------------------------------------------
> 
> Changes in V8:
>  -- Addressed the comments and fixed the bug caught by Hugh.
>  -- Updated the commit message for POSIX_FADV_WILLNEED asked by Minchan.
> 
> Changes in V7:
>  -- Use folio based interface, shmem_read_folio(), for FADV_WILLNEED.
>  -- Don't swap the SHM_LOCK'ed pages.
>  -- https://lore.kernel.org/all/cover.1676378702.git.quic_charante@quicinc.com/
> 
> Changes in V6:
>  -- Replaced the pages with folio's for shmem changes.
>  -- https://lore.kernel.org/all/cover.1675690847.git.quic_charante@quicinc.com/
> 
> Changes in V5:
>  -- Moved the 'endbyte' calculations to a header function for use by shmem_fadvise().
>  -- Addressed comments from suren.
>  -- No changes in resend. Retested on the latest tip.
>  -- https://lore.kernel.org/all/cover.1648706231.git.quic_charante@quicinc.com/
> 
> Changes in V4:
>   -- Changed the code to use reclaim_pages() to writeout the shmem pages to swap and then reclaim.
>   -- Addressed comments from Mark Hemment and Matthew.
>   -- fadvise() on shmem file may even unmap a page.
>   -- https://patchwork.kernel.org/project/linux-mm/patch/1644572051-24091-1-git-send-email-quic_charante@quicinc.com/
> 
> Changes in V3:
>   -- Considered THP pages while doing FADVISE_[DONT|WILL]NEED, identified by Matthew.
>   -- xarray used properly, as identified by Matthew.
>   -- Excluded mapped pages as it requires unmapping and the man pages of fadvise don't talk about them.
>   -- RESEND: Fixed the compilation issue when CONFIG_TMPFS is not defined.
>   -- https://patchwork.kernel.org/project/linux-mm/patch/1641488717-13865-1-git-send-email-quic_charante@quicinc.com/
> 
> Changes in V2:
>   -- Rearranged the code to not to sleep with rcu_lock while using xas_() functionality.
>   -- Addressed the comments from Suren.
>   -- https://patchwork.kernel.org/project/linux-mm/patch/1638442253-1591-1-git-send-email-quic_charante@quicinc.com/
> 
> changes in V1:
>   -- Created the interface for fadvise(2) to work on shmem files.
>   -- https://patchwork.kernel.org/project/linux-mm/patch/1633701982-22302-1-git-send-email-charante@codeaurora.org/
> 
> 
> Charan Teja Kalla (2):
>   mm: fadvise: move 'endbyte' calculations to helper function
>   mm: shmem: implement POSIX_FADV_[WILL|DONT]NEED for shmem
> 
>  mm/fadvise.c  |  11 +----
>  mm/internal.h |  21 ++++++++++
>  mm/shmem.c    | 127 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 149 insertions(+), 10 deletions(-)
>