From: Zeev Tarantov <zeev.tarantov@gmail.com>
Subject: Re: problem(?) in ext4 or mke2fs
Date: Sun, 3 Apr 2011 21:52:58 +0300
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References: <BANLkTi=gE-utOo479RU8qcWM99NpBrFmvQ@mail.gmail.com> <4D98BF34.6040503@redhat.com>
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To: Eric Sandeen <sandeen@redhat.com>
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On Sun, Apr 3, 2011 at 21:40, Eric Sandeen <sandeen@redhat.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 pro=
file output.
>> This was evidently because the command "mke2fs -t ext4 -m 0 -I 128 -=
O
>> ^has_journal,^ext_attr <block device>"
>> =A0created a filesystem with (output of tune2fs):
>> RAID stride: =A0 =A0 =A0 =A0 =A0 =A0 =A01
>> RAID stripe width: =A0 =A0 =A0 =A01
>
> mke2fs queries the block device for its geometry, based on what is
> reported via sysfs:
>
> /*
> =A0* Sets the geometry of a device (stripe/stride), and returns the
> =A0* device's alignment offset, if any, or a negative error.
> =A0*/
> static int get_device_geometry( ...
> ...
> =A0 =A0 =A0 =A0min_io =3D blkid_topology_get_minimum_io_size(tp);
> =A0 =A0 =A0 =A0opt_io =3D blkid_topology_get_optimal_io_size(tp);
> ...
>
> =A0 =A0 =A0 =A0fs_param->s_raid_stride =3D min_io / blocksize;
> =A0 =A0 =A0 =A0fs_param->s_raid_stripe_width =3D 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..=
=2E

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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