From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from a.ns.miles-group.at ([95.130.255.143] helo=radon.swed.at) by bombadil.infradead.org with esmtps (Exim 4.80.1 #2 (Red Hat Linux)) id 1Xu26m-0006qA-3E for linux-mtd@lists.infradead.org; Thu, 27 Nov 2014 16:39:56 +0000 Message-ID: <547753C0.6050604@nod.at> Date: Thu, 27 Nov 2014 17:39:28 +0100 From: Richard Weinberger MIME-Version: 1.0 To: dedekind1@gmail.com Subject: Re: [PATCH 2/6] UBI: Fastmap: Ensure that only one fastmap work is scheduled References: <1416835236-25185-1-git-send-email-richard@nod.at> <1416835236-25185-3-git-send-email-richard@nod.at> <1417102042.5858.102.camel@sauron.fi.intel.com> <54774DB7.5090200@nod.at> <1417106151.5858.122.camel@sauron.fi.intel.com> In-Reply-To: <1417106151.5858.122.camel@sauron.fi.intel.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Cc: linux-mtd@lists.infradead.org, linux-kernel@vger.kernel.org List-Id: Linux MTD discussion mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Am 27.11.2014 um 17:35 schrieb Artem Bityutskiy: > On Thu, 2014-11-27 at 17:13 +0100, Richard Weinberger wrote: >> Am 27.11.2014 um 16:27 schrieb Artem Bityutskiy: >>> On Mon, 2014-11-24 at 14:20 +0100, Richard Weinberger wrote: >>>> If the WL pool runs out of PEBs we schedule a fastmap write >>>> to refill it as soon as possible. >>>> Ensure that only one at a time is scheduled otherwise we might end in >>>> a fastmap write storm because writing the fastmap can schedule another >>>> write if bitflips are detected. >>> >>> Could you please provide some more details about the "write storm". Does >>> it happen when there are 2 fastmap works in the queue? Or if they run >>> simultaneously? Why the storm happens and white kind of "writes" it >>> consists of? >> >> If UBI needs to write a new fastmap while wear leveling (by using get_peb_for_wl()) >> a fastmap work is scheduled. >> We cannot write a fastmap in this context because we're in atomic context. >> At this point one fastmap write is scheduled. If now get_peb_for_wl() is executed >> a second time it will schedule another fastmap work because the pools are still not refilled. > > Sounds like just you do not need any works and any queues at all. All > you need is a "please, fastmap me!" flag. > > Then this flag should be checked every time we enter the background > thread or the fastmap code, and be acted upon. > > So the background thread would first check this flag, and if it is set - > call the fastmap stuff. The go do the WL works. > > Just off-the top of my head, take with grain of salt. So you want me to redesign it? IMHO this is just a matter of taste. Face it, my brain does not work like yours. I design things differently. Thanks, //richard