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]

Message-ID: <20090816150530.2bae6d1f@lxorguk.ukuu.org.uk>
Date:	Sun, 16 Aug 2009 15:05:30 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	James Bottomley <James.Bottomley@...e.de>
Cc:	Mark Lord <liml@....ca>, Chris Worley <worleys@...il.com>,
	Matthew Wilcox <matthew@....cx>,
	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 Sat, 15 Aug 2009 08:55:17 -0500
James Bottomley <James.Bottomley@...e.de> wrote:

> On Sat, 2009-08-15 at 09:22 -0400, Mark Lord wrote:
> > James Bottomley wrote:
> > >
> > > 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.
> > ..
> > 
> > I don't think that's really much of an issue -- we already have to do
> > that for cache-flushes whenever barriers are enabled.  Yes it costs,
> > but not too much.
> 
> That's not really what the enterprise is saying about flush barriers.
> True, not all the performance problems are NCQ queue drain, but for a
> steady workload they are significant.

Flush barriers are nightmare for more than enterprise. You drive
basically goes for a hike for a bit which trashes interactivity as well.
If the device can't do trim and the like without a drain I don't see much
point doing it at all, except maybe to wait for idle devices and run a
filesystem managed background 'strimmer' thread to just weed out now idle
blocks that have stayed idle - eg by adding an inode of all the deleted
untrimmed blocks and giving it an irregular empty ?

Alan
--
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/