Re: running mkfs.ext4 causes very high system load

[Nikola Ciprich <nikola.ciprich@linuxbox.cz>]

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hi Ted!

> Mke2fs generates a large number of writes, and with LVM, if you are
> writing a lot to an LV which uses physical disks shared by other LV's,
> ultimately you are going to run into disk contention.  It sounds like
> from your description that your system is pretty busy, and other
> applications are using the disks pretty heavily.
> 
> The other potential thing that could be happening is that mke2fs is
> dirtying a lot of memory blocks when it writes to the disk, and so
> your system is thrashing due memory pressure.

You're pretty right! After applying Your patch (+ one more small
fix to build on centos5) and using -D parameter, mkfs really got slower,
bud didn't affect system load almost at all!

> If it is caused by memory pressure it may be that using direct I/O
> will help make mke2fs be more "polite" at the expensive of taking a bit longer.
> 
> Here are patches versus the latest e2fsprogs (1.42.1) that might be
> helpful.  After you apply them, run mke2fs with the -D option to force
> the use of direct I/O.  Let me know if it makes a difference for you.

so it really made the difference. 

Thanks a lot!

with regards

nik


> 
> Regards,
> 
> 						 - Ted
> 
> diff --git a/lib/ext2fs/initialize.c b/lib/ext2fs/initialize.c
> index a63ea18..b06371c 100644
> --- a/lib/ext2fs/initialize.c
> +++ b/lib/ext2fs/initialize.c
> @@ -119,6 +119,8 @@ errcode_t ext2fs_initialize(const char *name, int flags,
>  	io_flags = IO_FLAG_RW;
>  	if (flags & EXT2_FLAG_EXCLUSIVE)
>  		io_flags |= IO_FLAG_EXCLUSIVE;
> +	if (flags & EXT2_FLAG_DIRECT_IO)
> +		io_flags |= IO_FLAG_DIRECT_IO;
>  	retval = manager->open(name, io_flags, &fs->io);
>  	if (retval)
>  		goto cleanup;
> diff --git a/misc/mke2fs.8.in b/misc/mke2fs.8.in
> index 8e78249..9f1fa29 100644
> --- a/misc/mke2fs.8.in
> +++ b/misc/mke2fs.8.in
> @@ -18,6 +18,9 @@ mke2fs \- create an ext2/ext3/ext4 filesystem
>  .I block-size
>  ]
>  [
> +.B \-D
> +]
> +[
>  .B \-f
>  .I fragment-size
>  ]
> @@ -184,6 +187,11 @@ Check the device for bad blocks before creating the file system.  If
>  this option is specified twice, then a slower read-write
>  test is used instead of a fast read-only test.
>  .TP
> +.B \-D
> +Use direct I/O when writing to the disk.  This avoids mke2fs dirtying a
> +lot of buffer cache memory which may impact other applications running
> +on a busy server, at the expense of causing mke2fs to run much more slowly.
> +.TP
>  .BI \-E " extended-options"
>  Set extended options for the filesystem.  Extended options are comma
>  separated, and may take an argument using the equals ('=') sign.  The
> diff --git a/misc/mke2fs.c b/misc/mke2fs.c
> index 51435d2..b8ff19b 100644
> --- a/misc/mke2fs.c
> +++ b/misc/mke2fs.c
> @@ -88,6 +88,7 @@ int	verbose;
>  int	quiet;
>  int	super_only;
>  int	discard = 1;	/* attempt to discard device before fs creation */
> +int	direct_io;
>  int	force;
>  int	noaction;
>  int	journal_size;
> @@ -1321,7 +1322,7 @@ profile_error:
>  	}
>  
>  	while ((c = getopt (argc, argv,
> -		    "b:cg:i:jl:m:no:qr:s:t:vC:E:FG:I:J:KL:M:N:O:R:ST:U:V")) != EOF) {
> +		    "b:cg:i:jl:m:no:qr:s:t:vC:DE:FG:I:J:KL:M:N:O:R:ST:U:V")) != EOF) {
>  		switch (c) {
>  		case 'b':
>  			blocksize = strtol(optarg, &tmp, 0);
> @@ -1354,6 +1355,9 @@ profile_error:
>  				exit(1);
>  			}
>  			break;
> +		case 'D':
> +			direct_io = 1;
> +			break;
>  		case 'g':
>  			fs_param.s_blocks_per_group = strtoul(optarg, &tmp, 0);
>  			if (*tmp) {
> @@ -2257,6 +2261,8 @@ int main (int argc, char *argv[])
>  	 * Initialize the superblock....
>  	 */
>  	flags = EXT2_FLAG_EXCLUSIVE;
> +	if (direct_io)
> +		flags |= EXT2_FLAG_DIRECT_IO;
>  	profile_get_boolean(profile, "options", "old_bitmaps", 0, 0,
>  			    &old_bitmaps);
>  	if (!old_bitmaps)
> 

-- 
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Ing. Nikola CIPRICH
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