From: Mark Lord Subject: Re: [PATCH 1/2] fs: Do not dispatch FITRIM through separate super_operation Date: Thu, 18 Nov 2010 16:37:34 -0500 Message-ID: <4CE59C9E.6050902@teksavvy.com> 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> Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Cc: Christoph Hellwig , Matthew Wilcox , Josef Bacik , Lukas Czerner , tytso@mit.edu, linux-ext4@vger.kernel.org, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, sandeen@redhat.com To: James Bottomley Return-path: In-Reply-To: <1290100750.3041.72.camel@mulgrave.site> Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-ext4.vger.kernel.org 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