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

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Message-ID: <x494obe4kd5.fsf@segfault.boston.devel.redhat.com>
Date:	Thu, 18 Nov 2010 12:22:46 -0500
From:	Jeff Moyer <jmoyer@...hat.com>
To:	James Bottomley <James.Bottomley@...e.de>
Cc:	Christoph Hellwig <hch@...radead.org>,
	Matthew Wilcox <matthew@....cx>,
	Josef Bacik <josef@...hat.com>,
	Lukas Czerner <lczerner@...hat.com>, tytso@....edu,
	linux-ext4@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, sandeen@...hat.com
Subject: Re: [PATCH 1/2] fs: Do not dispatch FITRIM through separate super_operation

James Bottomley <James.Bottomley@...e.de> writes:

> Not stepping into the debate: I'm happy to see punch go to the mapping
> data and FITRIM pick it up later.
>
> However, I think it's time to question whether we actually still want to
> allow online discard at all.  Most of the benchmarks show it to be a net

Define online discard, please.

> lose to almost everything (either SSD or Thinly Provisioned arrays), so
> it's become an "enable this to degrade performance" option with no
> upside.

Some SSDs very much require TRIMming to perform well as they age.  If
you're suggesting that we move from doing discards in journal commits to
a batched discard, like the one Lukas implemented, then I think that's
fine.  If we need to reintroduce the finer-grained discards due to some
hardware changes in the future, we can always do that.

Cheers,
Jeff
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