• H
    vfs: pagecache usage optimization for pagesize!=blocksize · 8ab22b9a
    Hisashi Hifumi 提交于
    When we read some part of a file through pagecache, if there is a
    pagecache of corresponding index but this page is not uptodate, read IO
    is issued and this page will be uptodate.
    
    I think this is good for pagesize == blocksize environment but there is
    room for improvement on pagesize != blocksize environment.  Because in
    this case a page can have multiple buffers and even if a page is not
    uptodate, some buffers can be uptodate.
    
    So I suggest that when all buffers which correspond to a part of a file
    that we want to read are uptodate, use this pagecache and copy data from
    this pagecache to user buffer even if a page is not uptodate.  This can
    reduce read IO and improve system throughput.
    
    I wrote a benchmark program and got result number with this program.
    
    This benchmark do:
    
      1: mount and open a test file.
    
      2: create a 512MB file.
    
      3: close a file and umount.
    
      4: mount and again open a test file.
    
      5: pwrite randomly 300000 times on a test file.  offset is aligned
         by IO size(1024bytes).
    
      6: measure time of preading randomly 100000 times on a test file.
    
    The result was:
    	2.6.26
            330 sec
    
    	2.6.26-patched
            226 sec
    
    Arch:i386
    Filesystem:ext3
    Blocksize:1024 bytes
    Memory: 1GB
    
    On ext3/4, a file is written through buffer/block.  So random read/write
    mixed workloads or random read after random write workloads are optimized
    with this patch under pagesize != blocksize environment.  This test result
    showed this.
    
    The benchmark program is as follows:
    
    #include <stdio.h>
    #include <sys/types.h>
    #include <sys/stat.h>
    #include <fcntl.h>
    #include <unistd.h>
    #include <time.h>
    #include <stdlib.h>
    #include <string.h>
    #include <sys/mount.h>
    
    #define LEN 1024
    #define LOOP 1024*512 /* 512MB */
    
    main(void)
    {
    	unsigned long i, offset, filesize;
    	int fd;
    	char buf[LEN];
    	time_t t1, t2;
    
    	if (mount("/dev/sda1", "/root/test1/", "ext3", 0, 0) < 0) {
    		perror("cannot mount\n");
    		exit(1);
    	}
    	memset(buf, 0, LEN);
    	fd = open("/root/test1/testfile", O_CREAT|O_RDWR|O_TRUNC);
    	if (fd < 0) {
    		perror("cannot open file\n");
    		exit(1);
    	}
    	for (i = 0; i < LOOP; i++)
    		write(fd, buf, LEN);
    	close(fd);
    	if (umount("/root/test1/") < 0) {
    		perror("cannot umount\n");
    		exit(1);
    	}
    	if (mount("/dev/sda1", "/root/test1/", "ext3", 0, 0) < 0) {
    		perror("cannot mount\n");
    		exit(1);
    	}
    	fd = open("/root/test1/testfile", O_RDWR);
    	if (fd < 0) {
    		perror("cannot open file\n");
    		exit(1);
    	}
    
    	filesize = LEN * LOOP;
    	for (i = 0; i < 300000; i++){
    		offset = (random() % filesize) & (~(LEN - 1));
    		pwrite(fd, buf, LEN, offset);
    	}
    	printf("start test\n");
    	time(&t1);
    	for (i = 0; i < 100000; i++){
    		offset = (random() % filesize) & (~(LEN - 1));
    		pread(fd, buf, LEN, offset);
    	}
    	time(&t2);
    	printf("%ld sec\n", t2-t1);
    	close(fd);
    	if (umount("/root/test1/") < 0) {
    		perror("cannot umount\n");
    		exit(1);
    	}
    }
    Signed-off-by: NHisashi Hifumi <hifumi.hisashi@oss.ntt.co.jp>
    Cc: Nick Piggin <nickpiggin@yahoo.com.au>
    Cc: Christoph Hellwig <hch@infradead.org>
    Cc: Jan Kara <jack@ucw.cz>
    Cc: <linux-ext4@vger.kernel.org>
    Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>
    8ab22b9a
filemap.c 70.0 KB