From mboxrd@z Thu Jan 1 00:00:00 1970 From: Christoph Hellwig Subject: Re: [RFC]raid5: add an option to avoid copy data from bio to stripe cache Date: Mon, 28 Apr 2014 03:17:48 -0700 Message-ID: <20140428101748.GA17026@infradead.org> References: <20140428065841.GA28726@kernel.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20140428065841.GA28726@kernel.org> Sender: linux-raid-owner@vger.kernel.org To: Shaohua Li Cc: neilb@suse.de, linux-raid@vger.kernel.org List-Id: linux-raid.ids On Mon, Apr 28, 2014 at 02:58:41PM +0800, Shaohua Li wrote: > > The stripe cache has two goals: > 1. cache data, so next time if data can be found in stripe cache, disk access > can be avoided. I think this is mostly a side effect. We have a much larger and better tuned page cache to take care of this. > 2. stable data. data is copied from bio to stripe cache and calculated parity. > data written to disk is from stripe cache, so if upper layer changes bio data, > data written to disk isn't impacted. > > In my environment, I can guarantee 2 will not happen. Why just in your environment? Now that we got stable pages in the page cache this should always be the case. > Of course, this shouldn't be enabled by default, so I added an option to > control it. Unless careful benchmarking in various scenarious shows adverse effects this should be the default. And if we can find adverse effects we need to look into them.