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Date:	Sun, 3 Apr 2011 21:52:58 +0300
From:	Zeev Tarantov <zeev.tarantov@...il.com>
To:	Eric Sandeen <sandeen@...hat.com>
Cc:	linux-ext4@...r.kernel.org
Subject: Re: problem(?) in ext4 or mke2fs

On Sun, Apr 3, 2011 at 21:40, Eric Sandeen <sandeen@...hat.com> wrote:
> On 4/3/11 11:07 AM, Zeev Tarantov wrote:
>> While testing zram I ran a script that creates a block devices,
>> creates a filesystem on in and untars Qt on that filesystem.
>> I was surprised to find ext4_mb_scan_aligned near the top of the profile output.
>> This was evidently because the command "mke2fs -t ext4 -m 0 -I 128 -O
>> ^has_journal,^ext_attr <block device>"
>>  created a filesystem with (output of tune2fs):
>> RAID stride:              1
>> RAID stripe width:        1
>
> mke2fs queries the block device for its geometry, based on what is
> reported via sysfs:
>
> /*
>  * Sets the geometry of a device (stripe/stride), and returns the
>  * device's alignment offset, if any, or a negative error.
>  */
> static int get_device_geometry( ...
> ...
>        min_io = blkid_topology_get_minimum_io_size(tp);
>        opt_io = blkid_topology_get_optimal_io_size(tp);
> ...
>
>        fs_param->s_raid_stride = min_io / blocksize;
>        fs_param->s_raid_stripe_width = opt_io / blocksize;
>
> What does
>
> # blockdev --getiomin --getioopt /dev/<yourdevice>
>
> say for your device?

get logical block (sector) size: 4096
get physical block (sector) size: 4096
get minimum I/O size: 4096
get optimal I/O size: 4096
get alignment offset in bytes: 0
get max sectors per request: 255
get blocksize: 4096
get readahead: 256

> The device may be reporting odd values, but mke2fs probably
> should be smart enough not to set block-sized stripe unit and width...

If the filesystem created with the default options is slow or has
higher cpu usage, it should be changed.

> -Eric

-Z.T.
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