From mboxrd@z Thu Jan 1 00:00:00 1970 From: Yuri Tikhonov Subject: Re[2]: [PATCH 07/11] md: rewrite handle_stripe_dirtying6 in asynchronous way Date: Fri, 16 Jan 2009 17:24:03 +0300 Message-ID: <1141743016.20090116172403@emcraft.com> References: <200812090057.33890.yur@emcraft.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7BIT Return-path: In-Reply-To: Sender: linux-raid-owner@vger.kernel.org To: Dan Williams Cc: linux-raid@vger.kernel.org, linuxppc-dev@ozlabs.org, dzu@denx.de, wd@denx.de, yanok@emcraft.com List-Id: linux-raid.ids On Friday, January 16, 2009 you wrote: > On Thu, Jan 15, 2009 at 2:51 PM, Dan Williams wrote: >> On Mon, Dec 8, 2008 at 2:57 PM, Yuri Tikhonov wrote: >> What's the reasoning behind changing the logic here, i.e. removing >> must_compute and such? I'd feel more comfortable seeing copy and >> paste where possible with cleanups separated out into their own patch. >> > Ok, I now see why this change was made. Please make this changelog > more descriptive than "Rewrite handle_stripe_dirtying6 function to > work asynchronously." Sure, how about the following: " md: rewrite handle_stripe_dirtying6 in asynchronous way Processing stripe dirtying in asynchronous way requires some changes to the handle_stripe_dirtying6() algorithm. In the synchronous implementation of the stripe dirtying we processed dirtying of a degraded stripe (with partially changed strip(s) located on the failed drive(s)) inside one handle_stripe_dirtying6() call: - we computed the missed strips from the old parities, and thus got the fully up-to-date stripe, then - we did reconstruction using the new data to write. In the asynchronous case of handle_stripe_dirtying6() we don't process anything right inside this function (since we under the lock), but only schedule the necessary operations with flags. Thus, if handle_stripe_dirtying6() is performed on the top of a degraded array we should schedule the reconstruction operation when the failed strips are marked (by previously called fetch_block6()) as to be computed (with the R5_Wantcompute flag), and all the other strips of the stripe are UPTODATE. The schedule_reconstruction() function will set the STRIPE_OP_POSTXOR flag [for new parity calculation], which is then handled in raid_run_ops() after the STRIPE_OP_COMPUTE_BLK one [which causes computing of the data missed]. " Regards, Yuri -- Yuri Tikhonov, Senior Software Engineer Emcraft Systems, www.emcraft.com