linux-kernel - Re: [PATCH v6] fat: Batched discard support for fat

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Date:	Tue, 24 May 2011 23:19:00 +0900
From:	OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
To:	Lukas Czerner <lczerner@...hat.com>
Cc:	Kyungmin Park <kmpark@...radead.org>,
	Arnd Bergmann <arnd@...db.de>, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH v6] fat: Batched discard support for fat

Lukas Czerner <lczerner@...hat.com> writes:

>> What is size of file system or underlying devices? You force to find the
>> device which target FS is using? Even if you can get size of underlying
>> devices, you force to user to insane loop in size of devices?
>
> Look, I do not have time to argue with you forever and I do not even
> understand what is your point. Just go and read other filesystems
> implementation of FITRIM (ext4,ext3,xfs,btrfs?) and you'll see what you
> need to do.
>
> If you do not want to get the file system size, then FINE! just pass the
> damn UULONG_MAX as length. I have no clue what insane loop are you
> talking about! It is *easy* just discard the whole thing (with
> UULONG_MAX) or, if you want to do it per-partes, then do it as long as
> it does not return EINVAL, once it does you know that your "start" is
> out of the filesystem and you are done!

You are not even understanding current implementations. See
ext3_trim_fs(), and ext4_trim_fs().

What happen if "start" was outside of max_blks:

ext3 returns 0
ext4 returns EINVAL

What means "start" is 0

ext3 maps to 1
ext4 just remove 0 from request

I missing something?

>> Why can you guarantee it's not big deal in design? Why can't you admit
>> userland can't make optimized loop?
>
> And what do you mean by that ?
>
> -Lukas

-- 
OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
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