linux-ext4 - Re: Is TRIM/DISCARD going to be a performance problem?

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Message-ID: <f3177b9e0905111503l1f8f8708u7fe95c34ff74f10a@mail.gmail.com>
Date:	Mon, 11 May 2009 16:03:38 -0600
From:	Chris Worley <worleys@...il.com>
To:	linux-fsdevel@...r.kernel.org, linux-ext4@...r.kernel.org
Subject: Re: Is TRIM/DISCARD going to be a performance problem?

 On Mon, May 11, 2009 at 6:48 AM, Matthew Wilcox <matthew@....cx> wrote:
>
> On Mon, May 11, 2009 at 02:43:25PM +0200, J??rn Engel wrote:
> > Given the hardware braindamage it is relatively sane.  As always, it
> > would be much better to fix the problem and not add workarounds, but we
> > seem to lack the gods favor this time around.
> >
> > Can't anyone explain to the SATA folks that a discard is much closer to
> > a write than to a secure erase or some other rare and slow command?
>
> I've heard the ATA committee are working on an NCQ version of TRIM.

Doesn't this fact make this discussion moot?

If the ATA committee knows they've got a problem, and are fixing it at
the level where the problem exists, why is Linux's job to fix at a
higher level?

The proposed solutions are going to consume CPU and slow down I/O
unnecessarily, as well as inefficiently dispatch Discards (i.e. the
longer the time between the discard and the reuse of a block, the
better).  If they are going to be implemented, then have a special
"brain-dead ATA mode" that doesn't inhibit solutions that can
implement Discard w/o the "queue draining" required by the broken
implementation.

Chris
P.S. Why was ext2/discard functionality removed?
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