From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from psmtp.com (na3sys010amx118.postini.com [74.125.245.118]) by kanga.kvack.org (Postfix) with SMTP id 27CE46B004A for ; Sun, 8 Apr 2012 09:50:27 -0400 (EDT) From: Alex Lemberg Date: Sun, 8 Apr 2012 06:50:16 -0700 Subject: RE: swap on eMMC and other flash Message-ID: References: <201203301744.16762.arnd@arndb.de> <201204021145.43222.arnd@arndb.de> <201204021455.25029.arnd@arndb.de> In-Reply-To: <201204021455.25029.arnd@arndb.de> Content-Language: en-US Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: quoted-printable MIME-Version: 1.0 Sender: owner-linux-mm@kvack.org List-ID: To: Arnd Bergmann Cc: "linaro-kernel@lists.linaro.org" , Rik van Riel , "linux-mmc@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "Luca Porzio (lporzio)" , "linux-mm@kvack.org" , Hyojin Jeong , "kernel-team@android.com" , Yejin Moon , Hugh Dickins , Yaniv Iarovici Hi Arnd, Regarding time to issue discard/TRIM commands: It would be advised to issue the discard command immediately after deleting= /freeing a SWAP cluster (i.e. as soon as it becomes available). Regarding SWAP page size: Working with as large as SWAP pages as possible would be recommended (prefe= rably 64KB). Also, writing in a sequential manner as much as possible while= swapping large quantities of data is also advisable. SWAP pages and corresponding transactions should be aligned to the SWAP pag= e size (i.e. 64KB above), the alignment should correspond to the physical s= torage "LBA 0", i.e. to the first LBA of the storage device (and not to a l= ogical/physical partition). Thanks, Alex > -----Original Message----- > From: Arnd Bergmann [mailto:arnd@arndb.de] > Sent: Monday, April 02, 2012 5:55 PM > To: Hugh Dickins > Cc: linaro-kernel@lists.linaro.org; Rik van Riel; linux- > mmc@vger.kernel.org; Alex Lemberg; linux-kernel@vger.kernel.org; Luca > Porzio (lporzio); linux-mm@kvack.org; Hyojin Jeong; kernel- > team@android.com; Yejin Moon > Subject: Re: swap on eMMC and other flash > > On Monday 02 April 2012, Hugh Dickins wrote: > > On Mon, 2 Apr 2012, Arnd Bergmann wrote: > > > > > > Another option would be batched discard as we do it for file > systems: > > > occasionally stop writing to swap space and scanning for areas that > > > have become available since the last discard, then send discard > > > commands for those. > > > > I'm not sure whether you've missed "swapon --discard", which switches > > on discard_swap_cluster() just before we allocate from a new cluster; > > or whether you're musing that it's no use to you because you want to > > repurpose the swap cluster to match erase block: I'm mentioning it in > > case you missed that it's already there (but few use it, since even > > done at that scale it's often more trouble than it's worth). > > I actually argued that discard_swap_cluster is exactly the right thing > to do, especially when clusters match erase blocks on the less capable > devices like SD cards. > > Luca was arguing that on some hardware there is no point in ever > submitting a discard just before we start reusing space, because > at that point it the hardware already discards the old data by > overwriting the logical addresses with new blocks, while > issuing a discard on all blocks as soon as they become available > would make a bigger difference. I would be interested in hearing > from Hyojin Jeong and Alex Lemberg what they think is the best > time to issue a discard, because they would know about other hardware > than Luca. > > Arnd PLEASE NOTE: The information contained in this electronic mail message is i= ntended only for the use of the designated recipient(s) named above. If the= reader of this message is not the intended recipient, you are hereby notif= ied that you have received this message in error and that any review, disse= mination, distribution, or copying of this message is strictly prohibited. = If you have received this communication in error, please notify the sender = by telephone or e-mail (as shown above) immediately and destroy any and all= copies of this message in your possession (whether hard copies or electron= ically stored copies). -- 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/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org