From: Roland Dreier <rdreier@cisco.com>
To: Greg Freemyer <greg.freemyer@gmail.com>
Cc: Richard Sharpe <realrichardsharpe@gmail.com>,
david@lang.hm, Markus Trippelsdorf <markus@trippelsdorf.de>,
Matthew Wilcox <willy@linux.intel.com>,
Hugh Dickins <hugh.dickins@tiscali.co.uk>,
Nitin Gupta <ngupta@vflare.org>, Ingo Molnar <mingo@elte.hu>,
Peter Zijlstra <peterz@infradead.org>,
linux-kernel@vger.kernel.org, linux-mm@kvack.org,
linux-scsi@vger.kernel.org, linux-ide@vger.kernel.org,
Linux RAID <linux-raid@vger.kernel.org>
Subject: Re: Discard support
Date: Fri, 14 Aug 2009 14:56:26 -0700 [thread overview]
Message-ID: <adafxbu3vqt.fsf@cisco.com> (raw)
In-Reply-To: <87f94c370908141433h111f819j550467bf31c60776@mail.gmail.com> (Greg Freemyer's message of "Fri, 14 Aug 2009 17:33:49 -0400")
> It seems to me that unmap is not all that different, why do we need to
> do it even close in time proximity to the deletes? With a bitmap, we
> have total timing control of when the unmaps are forwarded down to the
> device. I like that timing control much better than a cache and
> coalesce approach.
The trouble I see with a bitmap is the amount of memory it consumes. It
seems that discards must be tracked on no bigger than 4KB sectors (and
possibly even 512 byte sectors). But even with 4KB, then, say, a 32 TB
volume (just 16 * 2TB disks, or even lower end with thin provisioning)
requires 1 GB of bitmap memory. Which is a lot just to store, let alone
walk over etc.
- R.
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next prev parent reply other threads:[~2009-08-14 21:56 UTC|newest]
Thread overview: 90+ messages / expand[flat|nested] mbox.gz Atom feed top
2009-08-12 14:37 [PATCH] swap: send callback when swap slot is freed Nitin Gupta
2009-08-12 22:48 ` Hugh Dickins
2009-08-13 2:30 ` Nitin Gupta
2009-08-13 6:53 ` Peter Zijlstra
2009-08-13 14:44 ` Nitin Gupta
2009-08-13 17:45 ` Hugh Dickins
2009-08-13 2:41 ` Nitin Gupta
2009-08-13 5:05 ` compcache as a pre-swap area (was: [PATCH] swap: send callback when swap slot is freed) Al Boldi
2009-08-13 17:31 ` Nitin Gupta
2009-08-14 4:02 ` Al Boldi
2009-08-14 4:53 ` compcache as a pre-swap area Nitin Gupta
2009-08-14 15:49 ` Al Boldi
2009-08-15 11:00 ` Al Boldi
2009-08-13 15:13 ` Discard support (was Re: [PATCH] swap: send callback when swap slot is freed) Matthew Wilcox
2009-08-13 15:17 ` david
2009-08-13 15:26 ` Matthew Wilcox
2009-08-13 15:43 ` James Bottomley
2009-08-13 18:22 ` Ric Wheeler
2009-08-13 16:13 ` Nitin Gupta
2009-08-13 16:26 ` Markus Trippelsdorf
2009-08-13 16:33 ` david
2009-08-13 18:15 ` Greg Freemyer
2009-08-13 19:18 ` James Bottomley
2009-08-13 20:31 ` Richard Sharpe
2009-08-14 22:03 ` Mark Lord
2009-08-14 22:54 ` Greg Freemyer
2009-08-15 13:12 ` Mark Lord
2009-08-13 20:44 ` david
2009-08-13 20:54 ` Bryan Donlan
2009-08-14 22:10 ` Mark Lord
2009-08-14 23:21 ` Chris Worley
2009-08-14 23:45 ` Matthew Wilcox
2009-08-15 0:19 ` Chris Worley
2009-08-15 0:30 ` Greg Freemyer
2009-08-15 0:38 ` Chris Worley
2009-08-15 1:55 ` Greg Freemyer
2009-08-15 13:20 ` Mark Lord
2009-08-16 22:52 ` Chris Worley
2009-08-17 2:03 ` Mark Lord
2009-08-15 12:59 ` James Bottomley
2009-08-15 13:22 ` Mark Lord
2009-08-15 13:55 ` James Bottomley
2009-08-15 17:39 ` jim owens
2009-08-16 17:08 ` Robert Hancock
2009-08-16 14:05 ` Alan Cox
2009-08-16 14:16 ` Mark Lord
2009-08-16 15:34 ` Arjan van de Ven
2009-08-16 15:44 ` Theodore Tso
2009-08-16 17:28 ` Mark Lord
2009-08-16 17:37 ` Mark Lord
2009-08-16 17:37 ` Mark Lord
2009-08-17 16:30 ` Bill Davidsen
2009-08-17 16:56 ` jim owens
2009-08-17 17:14 ` Bill Davidsen
2009-08-17 17:37 ` jim owens
2009-08-16 15:52 ` James Bottomley
2009-08-16 16:32 ` Mark Lord
2009-08-16 18:07 ` James Bottomley
2009-08-16 18:19 ` Mark Lord
2009-08-16 18:24 ` James Bottomley
2009-08-17 16:37 ` Bill Davidsen
2009-08-17 17:08 ` Greg Freemyer
2009-08-17 17:19 ` James Bottomley
2009-08-17 18:16 ` Ric Wheeler
2009-08-17 18:21 ` Greg Freemyer
2009-08-17 19:18 ` James Bottomley
2009-08-17 20:19 ` Mark Lord
2009-08-17 20:28 ` James Bottomley
2009-08-17 20:28 ` Mark Lord
2009-08-16 16:59 ` Christoph Hellwig
2009-08-17 4:24 ` Douglas Gilbert
2009-08-17 13:56 ` James Bottomley
2009-08-17 14:10 ` Matthew Wilcox
2009-08-17 19:12 ` Christoph Hellwig
2009-08-17 19:24 ` James Bottomley
2009-08-16 21:50 ` Discard support Roland Dreier
2009-08-16 22:06 ` Jeff Garzik
2009-08-16 22:13 ` Theodore Tso
2009-08-16 22:51 ` Mark Lord
2009-08-16 19:29 ` Discard support (was Re: [PATCH] swap: send callback when swap slot is freed) Alan Cox
2009-08-16 23:05 ` John Robinson
2009-08-17 2:05 ` Mark Lord
2009-08-13 21:28 ` Greg Freemyer
2009-08-13 22:20 ` Richard Sharpe
2009-08-14 0:19 ` Greg Freemyer
[not found] ` <46b8a8850908131758s781b07f6v2729483c0e50ae7a@mail.gmail.com>
2009-08-14 21:33 ` Greg Freemyer
2009-08-14 21:56 ` Roland Dreier [this message]
2009-08-14 22:10 ` Discard support Greg Freemyer
2009-08-13 17:19 ` Discard support (was Re: [PATCH] swap: send callback when swap slot is freed) Hugh Dickins
2009-08-13 18:08 ` Douglas Gilbert
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