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

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Message-ID: <4A898FE4.1090104@tmr.com>
Date:	Mon, 17 Aug 2009 13:14:12 -0400
From:	Bill Davidsen <davidsen@....com>
To:	jim owens <jowens@...com>
CC:	Mark Lord <liml@....ca>, Theodore Tso <tytso@....edu>,
	Arjan van de Ven <arjan@...radead.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	James Bottomley <James.Bottomley@...e.de>,
	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)

jim owens wrote:
> Bill Davidsen wrote:
>>
>> I assume that it really is artificial, rather than the device really 
>> being ready for another operation (other than another TRIM). I lack 
>> the hardware, but the test would be the time to complete a read, trim 
>> and read, and two trim and read operations. Just my thought that the 
>> TRIM in progress may only block the next TRIM, rather than other 
>> operations.
>
> I don't know his test sequence but READ is not the likely command
> before and after TRIM unless we are talking about TRIM being issued
> only in delayed host garbage collection.  Filesystems send WRITES
> during delete.

My idea is to test using a command which will definitely not need to 
prepare the media before completion, thus read. If TRIM doesn't block 
reads, then NCQ may allow reads to take place. Because of buffering slow 
reads hurt more than slow writes in terms of user perception.

-- 
bill davidsen <davidsen@....com>
  CTO TMR Associates, Inc

"You are disgraced professional losers. And by the way, give us our money back."
    - Representative Earl Pomeroy,  Democrat of North Dakota
on the A.I.G. executives who were paid bonuses  after a federal bailout.


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