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Date: Tue, 23 Jul 2013 17:44:09 +0800
From: Robert Yang <liezhi.yang@...driver.com>
To: "Darrick J. Wong" <darrick.wong@...cle.com>
CC: <tytso@....edu>, <dvhart@...ux.intel.com>,
<linux-ext4@...r.kernel.org>
Subject: Re: [PATCH 2/2] debugfs.c: do sparse copy when src is a sparse file
Hi Darrick,
Thank you very much for your very detailed review, I will fix them
one by one and send a V2 sooner.
// Robert
On 07/23/2013 01:30 AM, Darrick J. Wong wrote:
> On Sun, Jul 21, 2013 at 10:38:12AM +0800, Robert Yang wrote:
>>
>> 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.
>
> Well in that case I'll review harder. :)
>
> (Actually I thought of a few more things this morning.)
>
>>
>> // 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@...driver.com>
>>>> Acked-by: Darren Hart <dvhart@...ux.intel.com>
>>>> ---
>>>> 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];
>
> I wonder, do we allow variable length arrays? I recall Ted was trying to get
> rid of these.
>
>>>
>>> ...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;
>
> I suspect that calloc()ing a zero buffer and calling memcmp() would be faster
> than a byte-for-byte comparison.
>
>>>> + 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;
>
> I think the entire make_holes clause could be lifted out of the inner while and
> placed in the outer while, since the is-zero-buffer test depends only on the
> input.
>
> You could use FIEMAP/FIBMAP or SEEK_DATA or something to efficiently walk the
> allocated regions of the incoming file. If they're available...
>
>>>> + }
>>>> + }
>>>> + /* Normal copy */
>>>> + if (got > 0) {
>
> Then you don't need the test here.
>
>>>> + *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) {
>
> Well, that's one way to detect a sparse file coming in -- but do we care about
> the case of copying in a non-sparse file that contains a lot of zero regions?
>
> Maybe we could add a flag to the 'write' command to force make_holes=1?
>
> (Or just figure it out ourselves via fiemap as suggested above.)
>
>>>> + 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.
>
> I don't think removing the extents flag is necessary; "touch /mnt/emptyfile"
> creates an empty flag with the extents flag set.
>
> --D
>>>> + */
>>>> + 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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>>>
>>>
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