Re: [PATCH 2/2] debugfs.c: do sparse copy when src is a sparse file

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Hi Darrick,

Thanks for your reply, it seems that 64K is a good idea since put 128K
on the stack might cause problems, I will wait for one or two days for
more comments on other parts of the patches, then send a V2 with the
updates.

// Robert


On 07/20/2013 02:55 AM, Darrick J. Wong wrote:
On Fri, Jul 19, 2013 at 10:17:37AM +0800, Robert Yang wrote:
Let debugfs do sparse copy when src is a sparse file, just like
"cp --sparse=auto"

* For the
   #define IO_BUFSIZE 32*1024

   This is from coreutils-8.13/src/ioblksize.h (GPL V3):
/* As of Mar 2009, 32KiB is determined to be the minimium
    blksize to best minimize system call overhead.
    This can be tested with this script with the results
    shown for a 1.7GHz pentium-m with 2GB of 400MHz DDR2 RAM:

Um.... GNU updated this to 64K a couple of years ago:
http://git.savannah.gnu.org/gitweb/?p=coreutils.git;a=blob;f=src/ioblksize.h;h=1ae93255e7d0ccf0855208c7ae5888209997bf16;hb=HEAD

Just for laughs I tried it on a T430 with an i5-3320M and 16G of DDR3-1600 RAM:

    1024=3.7 GB/s
    2048=7.1 GB/s
    4096=8.8 GB/s
    8192=14.9 GB/s
   16384=14.3 GB/s
   32768=13.4 GB/s
   65536=15.8 GB/s
  131072=20.7 GB/s
  262144=16.4 GB/s
  524288=15.9 GB/s
1048576=15.8 GB/s
2097152=15.1 GB/s
4194304=11.7 GB/s
8388608=9.9 GB/s
16777216=9.4 GB/s
33554432=9.3 GB/s
67108864=9.3 GB/s
134217728=8.8 GB/s

For that matter, a 2010-era i7-950/DDR3-1066 system showed this:

    1024=3.4 GB/s
    2048=5.6 GB/s
    4096=7.8 GB/s
    8192=9.5 GB/s
   16384=10.8 GB/s
   32768=11.4 GB/s
   65536=11.6 GB/s
  131072=12.2 GB/s
  262144=11.9 GB/s
  524288=12.3 GB/s
1048576=12.4 GB/s
2097152=12.5 GB/s
4194304=12.5 GB/s
8388608=10.3 GB/s
16777216=8.0 GB/s
33554432=7.6 GB/s
67108864=7.8 GB/s
134217728=7.5 GB/s

And for good measure, a cruddy old T2300 Core Duo from 2006 spat out this:

    1024=1.1 GB/s
    2048=2.1 GB/s
    4096=3.6 GB/s
    8192=5.0 GB/s
   16384=6.3 GB/s
   32768=6.5 GB/s
   65536=6.6 GB/s
  131072=7.0 GB/s
  262144=7.1 GB/s
  524288=7.1 GB/s
1048576=6.8 GB/s
2097152=4.4 GB/s
4194304=2.3 GB/s
8388608=2.0 GB/s
16777216=2.0 GB/s
33554432=2.0 GB/s
67108864=2.0 GB/s
134217728=1.9 GB/s

I suspect you could increase the buffer size to 128K (or possibly even BLKRAGET
size?) without much of a problem...


    for i in $(seq 0 10); do
      size=$((8*1024**3)) #ensure this is big enough
      bs=$((1024*2**$i))
      printf "%7s=" $bs
      dd bs=$bs if=/dev/zero of=/dev/null count=$(($size/$bs)) 2>&1 |
      sed -n 's/.* \([0-9.]* [GM]B\/s\)/\1/p'
    done

       1024=734 MB/s
       2048=1.3 GB/s
       4096=2.4 GB/s
       8192=3.5 GB/s
      16384=3.9 GB/s
      32768=5.2 GB/s
      65536=5.3 GB/s
     131072=5.5 GB/s
     262144=5.7 GB/s
     524288=5.7 GB/s
    1048576=5.8 GB/s

    Note that this is to minimize system call overhead.
    Other values may be appropriate to minimize file system
    or disk overhead.  For example on my current GNU/Linux system
    the readahead setting is 128KiB which was read using:

    file="."
    device=$(df -P --local "$file" | tail -n1 | cut -d' ' -f1)
    echo $(( $(blockdev --getra $device) * 512 ))

    However there isn't a portable way to get the above.
    In the future we could use the above method if available
    and default to io_blksize() if not.
  */
enum { IO_BUFSIZE = 32*1024 };

Signed-off-by: Robert Yang <liezhi.yang@xxxxxxxxxxxxx>
Acked-by: Darren Hart <dvhart@xxxxxxxxxxxxxxx>
---
  debugfs/debugfs.c | 70 +++++++++++++++++++++++++++++++++++++++++++++++--------
  1 file changed, 60 insertions(+), 10 deletions(-)

diff --git a/debugfs/debugfs.c b/debugfs/debugfs.c
index b77d0b5..e443703 100644
--- a/debugfs/debugfs.c
+++ b/debugfs/debugfs.c
@@ -37,6 +37,16 @@ extern char *optarg;
  #include "../version.h"
  #include "jfs_user.h"

+/* 32KiB is the minimium blksize to best minimize system call overhead. */
+#ifndef IO_BUFSIZE
+#define IO_BUFSIZE 32*1024
+#endif
+
+/* Block size for `st_blocks' */
+#ifndef S_BLKSIZE
+#define S_BLKSIZE 512
+#endif
+
  ss_request_table *extra_cmds;
  const char *debug_prog_name;
  int sci_idx;
@@ -1571,14 +1581,17 @@ void do_find_free_inode(int argc, char *argv[])
  }

  #ifndef READ_ONLY
-static errcode_t copy_file(int fd, ext2_ino_t newfile)
+static errcode_t copy_file(int fd, ext2_ino_t newfile, int bufsize,
+			int make_holes, int *zero_written)
  {
  	ext2_file_t	e2_file;
  	errcode_t	retval;
  	int		got;
  	unsigned int	written;
-	char		buf[8192];
+	char		buf[bufsize];

...well, I guess it could be more of a problem if you put 128K on the stack.

--D

  	char		*ptr;
+	char		*cp;
+	int		count;

  	retval = ext2fs_file_open(current_fs, newfile,
  				  EXT2_FILE_WRITE, &e2_file);
@@ -1594,14 +1607,30 @@ static errcode_t copy_file(int fd, ext2_ino_t newfile)
  			goto fail;
  		}
  		ptr = buf;
+		cp = ptr;
+		count = got;
  		while (got > 0) {
-			retval = ext2fs_file_write(e2_file, ptr,
-						   got, &written);
-			if (retval)
-				goto fail;
-
-			got -= written;
-			ptr += written;
+			if (make_holes) {
+				/* Check whether all is zero */
+				while (count-- && *cp++ == 0)
+					continue;
+				if (count < 0) {
+					 /* The whole block is zero, make a hole */
+					retval = ext2fs_file_lseek(e2_file, got, EXT2_SEEK_CUR, NULL);
+					if (retval)
+						goto fail;
+					got = 0;
+				}
+			}
+			/* Normal copy */
+			if (got > 0) {
+				*zero_written = 0;
+				retval = ext2fs_file_write(e2_file, ptr, got, &written);
+				if (retval)
+					goto fail;
+				got -= written;
+				ptr += written;
+			}
  		}
  	}
  	retval = ext2fs_file_close(e2_file);
@@ -1620,6 +1649,9 @@ void do_write(int argc, char *argv[])
  	ext2_ino_t	newfile;
  	errcode_t	retval;
  	struct ext2_inode inode;
+	int		bufsize = IO_BUFSIZE;
+	int		make_holes = 0;
+	int 		zero_written = 1;

  	if (common_args_process(argc, argv, 3, 3, "write",
  				"<native file> <new file>", CHECK_FS_RW))
@@ -1684,9 +1716,27 @@ void do_write(int argc, char *argv[])
  		return;
  	}
  	if (LINUX_S_ISREG(inode.i_mode)) {
-		retval = copy_file(fd, newfile);
+		if (statbuf.st_blocks < statbuf.st_size / S_BLKSIZE) {
+			make_holes = 1;
+			/*
+			 * Use I/O blocksize as buffer size when
+			 * copying sparse files.
+			 */
+			bufsize = statbuf.st_blksize;
+		}
+		retval = copy_file(fd, newfile, bufsize, make_holes, &zero_written);
  		if (retval)
  			com_err("copy_file", retval, 0);
+
+		if ((inode.i_flags & EXT4_EXTENTS_FL) && zero_written) {
+			/*
+			 * If no data is copied which indicateds that no write
+			 * happens, we need to turn off the EXT4_EXTENTS_FL.
+			 */
+			inode.i_flags &= ~EXT4_EXTENTS_FL;
+			if (debugfs_write_inode(newfile, &inode, argv[0]))
+				close(fd);
+		}
  	}
  	close(fd);
  }
--
1.8.1.2

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