From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail203.messagelabs.com (mail203.messagelabs.com [216.82.254.243]) by kanga.kvack.org (Postfix) with SMTP id 073486B004D for ; Wed, 18 Nov 2009 06:15:11 -0500 (EST) Received: by pwi9 with SMTP id 9so735027pwi.6 for ; Wed, 18 Nov 2009 03:15:10 -0800 (PST) MIME-Version: 1.0 In-Reply-To: <1258541696.3918.237.camel@laptop> References: <20091117161711.3DDA.A69D9226@jp.fujitsu.com> <20091117102903.7cb45ff3@lxorguk.ukuu.org.uk> <20091117200618.3DFF.A69D9226@jp.fujitsu.com> <4B029C40.2020803@gmail.com> <1258490826.3918.29.camel@laptop> <28c262360911171601u618ca555o1dd51ea19168575e@mail.gmail.com> <1258538181.3918.138.camel@laptop> <28c262360911180231o7fcd2128hc9c40f4fffa3f7d6@mail.gmail.com> <1258541696.3918.237.camel@laptop> Date: Wed, 18 Nov 2009 20:15:10 +0900 Message-ID: <28c262360911180315p6905c365we97f984c49c8fe18@mail.gmail.com> Subject: Re: [PATCH 2/7] mmc: Don't use PF_MEMALLOC From: Minchan Kim Content-Type: text/plain; charset=UTF-8 Sender: owner-linux-mm@kvack.org To: Peter Zijlstra Cc: KOSAKI Motohiro , Alan Cox , LKML , linux-mm , Andrew Morton , linux-mmc@vger.kernel.org List-ID: On Wed, Nov 18, 2009 at 7:54 PM, Peter Zijlstra wrote: > On Wed, 2009-11-18 at 19:31 +0900, Minchan Kim wrote: >> > >> > Sure some generic blocklevel infrastructure might work, _but_ you cannot >> > take away the responsibility of determining the amount of memory needed, >> > nor does any of this have any merit if you do not limit yourself to that >> > amount. >> >> Yes. Some one have to take a responsibility. >> >> The intention was we could take away the responsibility from block driver. >> Instead of driver, VM would take the responsibility. >> >> You mean althgouth VM could take the responsiblity, it is hard to >> expect amout of pages needed by block drivers? > > Correct, its near impossible for the VM to accurately guess the amount > of memory needed for a driver, or limit the usage of the driver. > > The driver could be very simple in that it'll just start a DMA on the > page and get an interrupt when done, not consuming much (if any) memory > beyond the generic BIO structure, but it could also be some iSCSI > monstrosity which involves the full network stack and userspace. Wow, Thanks for good example. Until now, I don't know iSCSI is such memory hog driver. > That is why I generally prefer the user of PF_MEMALLOC to take > responsibility, because it knows its own consumption and can limit its > own consumption. Okay. I understand your point by good explanation. > Now, I don't think (but I could be wring here) that you need to bother > with PF_MEMALLOC unless you're swapping. File based pages should always > be able to free some memory due to the dirty-limit, whcih basically > guarantees that there are some clean file pages for every dirty file > page. > > My swap-over-nfs series used to have a block-layer hook to expose the > swap-over-block behaviour: > > http://programming.kicks-ass.net/kernel-patches/vm_deadlock/v12.99/blk_queue_swapdev.patch > > That gives block devices the power to refuse being swapped over, which > could be an alternative to using PF_MEMALLOC. > Thanks for noticing me. I will look at your patches. Thanks again, Peter. -- Kind regards, Minchan Kim -- 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