linux-kernel - Re: Discard support (was Re: [PATCH] swap: send callback when swap slot is freed)

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Sat, 15 Aug 2009 07:59:36 -0500
From:	James Bottomley <James.Bottomley@...e.de>
To:	Chris Worley <worleys@...il.com>
Cc:	Matthew Wilcox <matthew@....cx>, Mark Lord <liml@....ca>,
	Bryan Donlan <bdonlan@...il.com>, david@...g.hm,
	Greg Freemyer <greg.freemyer@...il.com>,
	Markus Trippelsdorf <markus@...ppelsdorf.de>,
	Matthew Wilcox <willy@...ux.intel.com>,
	Hugh Dickins <hugh.dickins@...cali.co.uk>,
	Nitin Gupta <ngupta@...are.org>, Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <peterz@...radead.org>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	linux-scsi@...r.kernel.org, linux-ide@...r.kernel.org,
	Linux RAID <linux-raid@...r.kernel.org>
Subject: Re: Discard support (was Re: [PATCH] swap: send callback when swap
  slot is freed)

On Fri, 2009-08-14 at 18:19 -0600, Chris Worley wrote:
> On Fri, Aug 14, 2009 at 5:45 PM, Matthew Wilcox<matthew@....cx> wrote:
> > On Fri, Aug 14, 2009 at 05:21:32PM -0600, Chris Worley wrote:
> >> Sooner is better than waiting to coalesce.  The longer an LBA is
> >> inactive, the better for any management scheme.  If you wait until
> >> it's reused, you might as well forgo the advantages of TRIM/UNMAP.  If
> >> a the controller wants to coalesce, let it coalesce.
> >
> > I'm sorry, you're wrong.  There is a tradeoff point, and it's different
> > for each drive model.  Sending down a steady stream of tiny TRIMs is
> > going to give terrible performance.
> 
> Sounds like you might be using junk for a device?
> 
> For junk, a little coalescing may be warranted... like in the I/O
> schedular, but no more than 100usecs wait before posting, or then you
> effect high performing devices too.

Um, I think you missed the original point in all of this at the
beginning of the thread:  On ATA TRIM commands cannot be tagged.  This
means you have to drain the outstanding NCQ commands (stalling the
device) before you can send a TRIM.   If we do this for every discard,
the performance impact will be pretty devastating, hence the need to
coalesce.  It's nothing really to do with device characteristics, it's
an ATA protocol problem.

James


--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/