Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757228Ab1F0NnE (ORCPT ); Mon, 27 Jun 2011 09:43:04 -0400 Received: from mail-pv0-f174.google.com ([74.125.83.174]:54692 "EHLO mail-pv0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754835Ab1F0Nmj (ORCPT ); Mon, 27 Jun 2011 09:42:39 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=from:to:cc:subject:date:message-id:x-mailer:in-reply-to:references; b=NbYgoxFpyxjgt6czUCa3cOI0v+x0E663cNANFQzmcRtbOCSS591oqSg51OTUBo8sWA 9yxRYgOlmcHoxB3mF7Lt+eNDp8VwmwtCjF9sxPKqgspvtVkJz0beiUfVVmn1iilQpcNO KYRae51HKKd8GDMnZZHLcs7hTarb6mQ40ro1g= From: Geunsik Lim To: Ingo Molnar , Andrew Morton , Peter Zijlstra , Hugh Dickins , Steven Rostedt Cc: Thomas Gleixner , "H. Peter Anvin" , Darren Hart , linux-kernel , linux-mm Subject: [PATCH V2 4/4] munmap: documentation of munmap operation interface Date: Mon, 27 Jun 2011 22:41:56 +0900 Message-Id: <1309182116-26698-5-git-send-email-leemgs1@gmail.com> X-Mailer: git-send-email 1.7.3.4 In-Reply-To: <1309182116-26698-1-git-send-email-leemgs1@gmail.com> References: <1309182116-26698-1-git-send-email-leemgs1@gmail.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3469 Lines: 98 From: Geunsik Lim kernel documentation to utilize flexible memory unmap operation interface for the ideal scheduler latency. Signed-off-by: Geunsik Lim Acked-by: Hyunjin Choi CC: Andrew Morton CC: Peter Zijlstra CC: Steven Rostedt CC: Hugh Dickins CC: Randy Dunlap CC: Ingo Molnar --- Documentation/sysctl/vm.txt | 36 ++++++++++++++++++++++++++++++++++++ MAINTAINERS | 7 +++++++ 2 files changed, 43 insertions(+), 0 deletions(-) diff --git a/Documentation/sysctl/vm.txt b/Documentation/sysctl/vm.txt index 30289fa..5d70098 100644 --- a/Documentation/sysctl/vm.txt +++ b/Documentation/sysctl/vm.txt @@ -40,6 +40,7 @@ Currently, these files are in /proc/sys/vm: - min_slab_ratio - min_unmapped_ratio - mmap_min_addr +- munmap_unit_size - nr_hugepages - nr_overcommit_hugepages - nr_pdflush_threads @@ -409,6 +410,42 @@ against future potential kernel bugs. ============================================================== +munmap_unit_size + +unmap_vmas(= unmap a range of memory covered by a list of vma) is treading +a delicate and uncomfortable line between high performance and low latency. +We've chosen to improve performance at the expense of latency. + +So although there may be no need to reschedule right now, +if we keep on gathering more and more memory without flushing, +we'll be very unresponsive when a reschedule is needed later on. + +Consider the best suitable result between high performance and low latency +on preemptive mode or non-preemptive mode. Select optimal munmap size to +return memory space that is allocated by mmap system call. + +For example, for recording mass files, if we try to unmap memory that we +allocated with 100MB for recording in embedded devices, we have to wait +for more than 3 seconds to change mode from play mode to recording mode. +This results from the unit of memory unmapped size when we are recording +mass files like camcorder particularly. + +This value can be changed after boot using the +/proc/sys/vm/munmap_unit_size tunable. + +Examples: + 2048 => 8,388,608 bytes : for straight-line efficiency + 1024 => 4,194,304 bytes + 512 => 2,097,152 bytes + 256 => 1,048,576 bytes + 128 => 524,288 bytes + 64 => 262,144 bytes + 32 => 131,072 bytes + 16 => 65,536 bytes + 8 => 32,768 bytes : for low-latency + +============================================================== + nr_hugepages Change the minimum size of the hugepage pool. diff --git a/MAINTAINERS b/MAINTAINERS index 1380312..3f1960a 100644 --- a/MAINTAINERS +++ b/MAINTAINERS @@ -4128,6 +4128,12 @@ L: linux-mm@kvack.org S: Maintained F: mm/memcontrol.c +MEMORY UNMAP OPERATION UNIT INTERFACE +M: Geunsik Lim +S: Maintained +F: mm/munmap_unit_size.c +F: include/linux/munmap_unit_size.h + MEMORY TECHNOLOGY DEVICES (MTD) M: David Woodhouse L: linux-mtd@lists.infradead.org -- 1.7.3.4 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/