linux-kernel - Re: [PATCH] [RESEND] fs: cachefiles: Add support for large files in filesystem caching

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Date:	Wed, 20 Jun 2012 21:45:57 +0200
From:	Justin <jlec@...too.org>
To:	Suresh Jayaraman <sjayaraman@...e.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	David Howells <dhowells@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>, linux-cachefs@...hat.com
Subject: Re: [PATCH] [RESEND] fs: cachefiles: Add support for large files
 in filesystem caching

On 20.06.2012 15:35, Suresh Jayaraman wrote:
> On 06/19/2012 01:22 PM, Andrew Morton wrote:
>> On Tue, 19 Jun 2012 10:57:27 +0530 Suresh Jayaraman <sjayaraman@...e.com> wrote:
>>
>>>> How extensively was this change tested?  Please describe the testing
>>>> which was performed?
>>>>
>>>
>>> The original patch was tested by mounting a NFS share with fscache
>>> option enabled, do a md5sum on a nfs file larger than 2GB and ensure
>>> that the file is getting cached by fscache (watch cache size growing)
>>> on x86_64. 
>>
>> Well it will need a lot more coverage testing than that.  truncate? 
>> expanding truncate?  write, lseek, pwrite, pread(), mmap(MAP_SHARED),
>> behavior at the new max file size (what is that?), etc.
>>
> 
> The changelog could be slightly misleading as the patch doesn't really
> add LFS support. It just passes O_LARGEFILE flag to dentry_open() to make
> VFS allow cachefiles to open larger files (instead of failing it with
> -EOVERFLOW). Cachefiles is just a cache that uses the VFS/VM interfaces to
> get another disk filesystem to do the requisite I/O on its behalf.
> So, I doubt whether more coverage testing is required for this change.
> 
> Anyway, I'm attaching a quick and dirty test program that might help
> (not well tested though). I'm unable to to test it as I have modified
> my setup and have to redo it.
> 
> Justin, do you have the setup and can you get this tested?
> 
> 
> 
> /*
>  * Few tests to ensure LFS (Large File Support) is working correctly.
>  *
>  * The requests (seek, truncate, write, mmap etc) that extend beyond the offset
>  * maximum (off_t) should succeed.
>  *
>  * Compile it with -D_FILE_OFFSET_BITS=64
>  *
>  * Run it like:
>  * 	./lfs-tests large_file
>  *
>  */
> #include <stdio.h>
> #include <stdlib.h>
> #include <string.h>
> #include <fcntl.h>
> #include <unistd.h>
> #include <sys/types.h>
> #include <sys/stat.h>
> #include <sys/mman.h>
> 
> #define BUF_SZ 32
> 
> #define err(msg) \
> 	do { perror(msg); exit(EXIT_FAILURE); } while (0)
> 
> 
> void report_size(int fd, struct stat *st)
> {
> 	fstat(fd, st);
> 	printf("size of file: %ld\n", st->st_size);
> 
> 	return;
> }
> 
> int main(int argc, char *argv[])
> {
> 	int fd;
> 	int rc = 0;
> 	unsigned long offset = 0;
> 	struct stat stbuf;
> 	char buf[BUF_SZ];
> 	void *file_mem;
> 
> 	if (argc != 2) {
> 		fprintf(stderr, "Usage: %s test_file\n", argv[0]);
> 		exit(EXIT_FAILURE);
> 	}
> 
> 	fd = open(argv[1], O_RDWR | O_APPEND);
> 	if (fd == -1)
> 		err("open");
> 
> 	memset(buf, 0, sizeof(buf));
> 
> 	/* seek to the end of file */
> 	offset = lseek(fd, 0, SEEK_END);
> 	if (offset < 0)
> 		err("lseek");
> 
> 	/* seek past the end of file */
> 	offset = lseek(fd, BUF_SZ, SEEK_END);
> 	printf("%ld\n", offset);
> 	if (offset < 0)
> 		err("lseek");
> 
> 	/* truncate it to < 2GB and report size */
> 	rc = ftruncate(fd, 2147483648 - BUF_SZ);
> 	if (rc != 0)
> 		err("ftruncate");
> 
> 	report_size(fd, &stbuf);
> 
> 	/* truncate it to a size larger than 2GB */
> 	rc = ftruncate(fd, 4294967360);
> 	if (rc != 0)
> 		err("ftruncate");
> 
> 	report_size(fd, &stbuf);
> 
> 	/* seek to the end of file */
> 	offset = lseek(fd, 0, SEEK_END);
> 	if (offset < 0)
> 		err("lseek");
> 
> 	memset(buf, 'a', sizeof(buf));
> 
> 	/* write past 4GB */
> 	rc = write(fd, buf, sizeof(buf));
> 	if (rc == -1)
> 		err("write");
> 
> 	report_size(fd, &stbuf);
> 
> 	offset = lseek(fd, 0, SEEK_END);
> 	if (offset < 0)
> 		err("lseek");
> 
> 	/* pwrite and pread */
> 	rc = pread(fd, buf, BUF_SZ, offset);
> 	if (rc == -1)
> 		err("pread");
> 
> 	rc = pwrite(fd, buf, sizeof(buf), offset);
> 	if (rc == -1) 
> 		err("pwrite");
> 
> 	report_size(fd, &stbuf);
> 
> 	/* page align offset */
> 	offset = offset & ~(sysconf(_SC_PAGE_SIZE) - 1);
> 
> 	file_mem = mmap(0, BUF_SZ, PROT_WRITE, MAP_SHARED, fd, offset);
> 	if (file_mem == MAP_FAILED)
> 		err("mmap");
> 
> 	munmap(file_mem, 64);
> 
> 	close(fd);
> 
> 	return EXIT_SUCCESS;
> }
> 

Hi,

so here are my test. Both system with fscache enabled.

unpatched kernel (Opensuse 12.1 linux-3.1.10-1.9-default):

$ ./large_file foo
8589934624
size of file: 2147483616
size of file: 4294967360
size of file: 4294967392
size of file: 4294967424


patched kernel (Gentoo Linux linux-3.4.3):


$ ./large_file bar
8589934624
size of file: 2147483616
size of file: 4294967360
size of file: 4294967392
size of file: 4294967424


no crash, everything worked.


Thanks justin




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