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Date: Mon, 25 Apr 2011 19:44:32 +0900 From: Geunsik Lim <leemgs1@...il.com> To: Ingo Molnar <mingo@...e.hu>, Andrew Morton <akpm@...ux-foundation.org> Cc: Peter Zijlstra <a.p.zijlstra@...llo.nl>, Thomas Gleixner <tglx@...utronix.de>, "H. Peter Anvin" <hpa@...or.com>, Hugh Dickins <hughd@...gle.com>, Steven Rostedt <rostedt@...dmis.org>, Darren Hart <dvhart@...ux.intel.com>, linux-kernel <linux-kernel@...r.kernel.org>, linux-rt-users <linux-rt-users@...r.kernel.org> Subject: [PATCH 4/4] munmap: documentation of munmap operation interface From: Geunsik Lim <geunsik.lim@...sung.com> kernel documentation to utilize flexible memory unmap operation interface for the ideal scheduler latency. Signed-off-by: Geunsik Lim <geunsik.lim@...sung.com> Acked-by: Hyunjin Choi <hj89.choi@...sung.com> --- 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..9dc4c0a 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 +410,41 @@ 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 hi-performance and low-latency. +We've chosen to improve performance at the expense of latency. + +So although there may be no need to resched right now, +if we keep on gathering more and more without flushing, +we'll be very unresponsive when a resched is needed later on. + +Consider the best suitable result between high performance and low latency +on preemption 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 3seconds 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 => 8,388,608bytes : for straight-line efficiency + 1024 => 4,194,304bytes + 512 => 2,097,152bytes + 256 => 1,048,576bytes + 128 => 524,288bytes + 64 => 262,144bytes + 32 => 131,072bytes + 16 => 65,536bytes + 8 => 32,768bytes : for low-latency + +============================================================== + nr_hugepages Change the minimum size of the hugepage pool. diff --git a/MAINTAINERS b/MAINTAINERS index 1380312..07f4123 100644 --- a/MAINTAINERS +++ b/MAINTAINERS @@ -4128,6 +4128,13 @@ L: linux-mm@...ck.org S: Maintained F: mm/memcontrol.c +MEMORY UNMAP OPERATION UNIT INTERFACE +M: Geunsik Lim <geunsik.lim@...sung.com> +L: linux-rt-users@...r.kernel.org +S: Maintained +F: mm/munmap_unit_size.c +F: include/linux/munmap_unit_size.h + MEMORY TECHNOLOGY DEVICES (MTD) M: David Woodhouse <dwmw2@...radead.org> L: linux-mtd@...ts.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@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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