linux-ext4 - Re: [PATCH 1/2] fs: Do not dispatch FITRIM through separate super

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Date:	Tue, 7 Dec 2010 04:27:49 -0500
From:	Christoph Hellwig <hch@...radead.org>
To:	Mark Lord <kernel@...savvy.com>
Cc:	Christoph Hellwig <hch@...radead.org>,
	Chris Mason <chris.mason@...cle.com>,
	James Bottomley <james.bottomley@...e.de>,
	Matthew Wilcox <matthew@....cx>,
	Josef Bacik <josef@...hat.com>,
	Lukas Czerner <lczerner@...hat.com>, tytso <tytso@....edu>,
	linux-ext4 <linux-ext4@...r.kernel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	sandeen <sandeen@...hat.com>
Subject: Re: [PATCH 1/2] fs: Do not dispatch FITRIM through separate
 super_operation

On Fri, Nov 19, 2010 at 10:21:35AM -0500, Mark Lord wrote:
> >I really hate to rely on this third party hearsay (from all sides), and
> >have implement TRIM support in qemu now.  I'll soon install win7 and
> >will check out the TRIM patters myself.
> 
> Excellent!

I did a Windows 7 installation under qemu today, and the result is:

 - it TRIMs the whole device early during the installation
 - after that I see a constant stream of small trims during the
   installation.  It's using lots of non-contiguous ranges in a single
   TRIM command, with sizes down to 8 sectors (4k) for a single range.
 - after installation there's is some background-trimming going on
   even when doing no user interaction with the VM at all.
 - removing files leads to an instant stream of TRIMs, again vectored
   and of all sizes down to 4k.  Note that the TRIMs are a lot more
   instant than even with btrfs and -o discard, which delays most
   TRIMs until doing a sync.
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