From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail138.messagelabs.com (mail138.messagelabs.com [216.82.249.35]) by kanga.kvack.org (Postfix) with SMTP id 53F336B004D for ; Thu, 13 Aug 2009 16:54:48 -0400 (EDT) Received: by ewy18 with SMTP id 18so1141056ewy.38 for ; Thu, 13 Aug 2009 13:54:54 -0700 (PDT) MIME-Version: 1.0 In-Reply-To: References: <200908122007.43522.ngupta@vflare.org> <20090813151312.GA13559@linux.intel.com> <20090813162621.GB1915@phenom2.trippelsdorf.de> <87f94c370908131115r680a7523w3cdbc78b9e82373c@mail.gmail.com> From: Bryan Donlan Date: Thu, 13 Aug 2009 16:54:34 -0400 Message-ID: <3e8340490908131354q167840fcv124ec56c92bbb830@mail.gmail.com> Subject: Re: Discard support (was Re: [PATCH] swap: send callback when swap slot is freed) Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable Sender: owner-linux-mm@kvack.org To: david@lang.hm Cc: Greg Freemyer , Markus Trippelsdorf , Matthew Wilcox , Hugh Dickins , Nitin Gupta , Ingo Molnar , Peter Zijlstra , linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-scsi@vger.kernel.org, linux-ide@vger.kernel.org, Linux RAID List-ID: On Thu, Aug 13, 2009 at 4:44 PM, wrote: > On Thu, 13 Aug 2009, Greg Freemyer wrote: > >> On Thu, Aug 13, 2009 at 12:33 PM, wrote: >>> >>> On Thu, 13 Aug 2009, Markus Trippelsdorf wrote: >>> >>>> On Thu, Aug 13, 2009 at 08:13:12AM -0700, Matthew Wilcox wrote: >>>>> >>>>> I am planning a complete overhaul of the discard work. =A0Users can s= end >>>>> down discard requests as frequently as they like. =A0The block layer = will >>>>> cache them, and invalidate them if writes come through. =A0Periodical= ly, >>>>> the block layer will send down a TRIM or an UNMAP (depending on the >>>>> underlying device) and get rid of the blocks that have remained >>>>> unwanted >>>>> in the interim. >>>> >>>> That is a very good idea. I've tested your original TRIM implementatio= n >>>> on >>>> my Vertex yesterday and it was awful ;-). The SSD needs hundreds of >>>> milliseconds to digest a single TRIM command. And since your >>>> implementation >>>> sends a TRIM for each extent of each deleted file, the whole system is >>>> unusable after a short while. >>>> An optimal solution would be to consolidate the discard requests, bund= le >>>> them and send them to the drive as infrequent as possible. >>> >>> or queue them up and send them when the drive is idle (you would need t= o >>> keep track to make sure the space isn't re-used) >>> >>> as an example, if you would consider spinning down a drive you don't hu= rt >>> performance by sending accumulated trim commands. >>> >>> David Lang >> >> An alternate approach is the block layer maintain its own bitmap of >> used unused sectors / blocks. Unmap commands from the filesystem just >> cause the bitmap to be updated. =A0No other effect. > > how does the block layer know what blocks are unused by the filesystem? > > or would it be a case of the filesystem generating discard/trim requests = to > the block layer so that it can maintain it's bitmap, and then the block > layer generating the requests to the drive below it? Perhaps an interface (ioctl, etc) can be added to ask a filesystem to discard all unused blocks in a certain range? (That is, have the filesystem validate the request under any necessary locks before passing it to the block IO layer) -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org