Message-ID: <4CE59C9E.6050902@teksavvy.com>
Date: Thu, 18 Nov 2010 16:37:34 -0500
From: Mark Lord <kernel@teksavvy.com>
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To: James Bottomley <James.Bottomley@suse.de>
CC: Christoph Hellwig <hch@infradead.org>, Matthew Wilcox <matthew@wil.cx>,
        Josef Bacik <josef@redhat.com>, Lukas Czerner <lczerner@redhat.com>,
        tytso@mit.edu, linux-ext4@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
        sandeen@redhat.com
Subject: Re: [PATCH 1/2] fs: Do not dispatch FITRIM through separate super_operation
References: <1290065809-3976-1-git-send-email-lczerner@redhat.com>	 <20101118130630.GJ6178@parisc-linux.org>	 <20101118134804.GN5618@dhcp231-156.rdu.redhat.com>	 <20101118141957.GK6178@parisc-linux.org>	 <20101118142918.GA18510@infradead.org> <1290100750.3041.72.camel@mulgrave.site>
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On 10-11-18 12:19 PM, James Bottomley wrote:
>
> 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
> lose to almost everything (either SSD or Thinly Provisioned arrays), so
> it's become an "enable this to degrade performance" option with no
> upside.

I also suspect that online TRIM exerts significant premature wear on the SSDs.
TRIM operations most likely trigger immediate copy/erase operations internal
to most SSDs, often regardless of the amount of data being trimmed.

Performing a 256KB erase because of a 1024-byte TRIM, over and over, is going
to harm the expected lifetime of an SSD.  Sure, some SSDs may do things differently
internally, but I don't see it working that way in much of the current crop of SSDs.

Currently, I patch my kernels to remove the automatic online TRIMs.
Is there a knob somewhere for this in the later kernels?

Cheers
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