linux-ext4 - Re: [PATCH v2] ext4: dynamical adjust the length of zero-out chunk

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Message-ID: <20120813173224.GF9117@lenny.home.zabbo.net>
Date:	Mon, 13 Aug 2012 10:32:24 -0700
From:	Zach Brown <zab@...hat.com>
To:	"Theodore Ts'o" <tytso@....edu>
Cc:	Andreas Dilger <adilger@...ger.ca>,
	Zheng Liu <wenqing.lz@...bao.com>,
	Eric Sandeen <sandeen@...hat.com>,
	Zheng Liu <gnehzuil.liu@...il.com>,
	ext4 development <linux-ext4@...r.kernel.org>
Subject: Re: [PATCH v2] ext4: dynamical adjust the length of zero-out chunk

> I also reworded the commit description slightly, and this is what I
> currently have in my tree.  What do people think?

(well, you asked! :))

>     we allow it to be tunable via sysfs and set an initial default value
>     of 32, so instead of creating uninitalized extents smaller than

s/32/16/?

>     256k (assuming a 4k block size), they will be zeroed out instead.

Having to qualify the zeroout len with the block size caught my
attention!

> --- a/fs/ext4/super.c
> +++ b/fs/ext4/super.c
> @@ -2541,6 +2541,7 @@ EXT4_RW_ATTR_SBI_UI(mb_order2_req, s_mb_order2_reqs);
>  EXT4_RW_ATTR_SBI_UI(mb_stream_req, s_mb_stream_request);
>  EXT4_RW_ATTR_SBI_UI(mb_group_prealloc, s_mb_group_prealloc);
>  EXT4_RW_ATTR_SBI_UI(max_writeback_mb_bump, s_max_writeback_mb_bump);
> +EXT4_RW_ATTR_SBI_UI(extent_zeroout_len, s_extent_zeroout_len);
>  EXT4_ATTR(trigger_fs_error, 0200, NULL, trigger_test_error);

"len" seems to stand out amongst all those "mb" names :)

It'd be nice to define the tunable in terms of some fixed unit, kb or
mb, whatever, and then translate to the block size in the code so people
don't have to do that math by hand.

No?

- z
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