From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail172.messagelabs.com (mail172.messagelabs.com [216.82.254.3]) by kanga.kvack.org (Postfix) with SMTP id 2FC6A5F0001 for ; Tue, 14 Apr 2009 10:26:21 -0400 (EDT) From: Nick Piggin Subject: Re: [RFC][PATCH v3 1/6] mm: Don't unmap gup()ed page Date: Wed, 15 Apr 2009 00:26:34 +1000 References: <20090414151204.C647.A69D9226@jp.fujitsu.com> <2f11576a0904140639l426e137ewdc46296cdb377dd@mail.gmail.com> <20090414141209.GB31644@random.random> In-Reply-To: <20090414141209.GB31644@random.random> MIME-Version: 1.0 Content-Disposition: inline Message-Id: <200904150026.36142.nickpiggin@yahoo.com.au> Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org To: Andrea Arcangeli Cc: KOSAKI Motohiro , LKML , Linus Torvalds , Andrew Morton , Jeff Moyer , linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, Hugh Dickins List-ID: On Wednesday 15 April 2009 00:12:09 Andrea Arcangeli wrote: > On Tue, Apr 14, 2009 at 10:39:54PM +0900, KOSAKI Motohiro wrote: > > I guess you dislike get_user_page_fast() grab pte_lock too, right? > > If get_user_page_fast is vetoed to run a set_bit on the already cache > hot and exclusive struct page, I doubt taking a potentially cache > cold, mm-wide or pmd-wide pte_lock is ok. Yes, I'd *really* rather not. I actually implemented gup_fast in response to problem reported with DB2 workload hitting the ptl (and not the more obvious mmap_sem, although certainly they had some gain from removing that cacheline as well). gup_fast iirc is worth nearly 10% on a 4 socket x86 system with DB2. That's the same order of magnitude as the speedups quoted to justify the addition of hugepages, or O_DIRECT itself. Andrea: I didn't veto that set_bit change of yours as such. I just noted there could be more atomic operations. Actually I would welcome more comparison between our two approaches, but they seem to be stuck with Linus refusing (I think) to copy the page at fork() time :( -- 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