From: Geunsik Lim <geunsik.lim@xxxxxxxxxxx> kernel documentation to utilize flexible memory unmap operation interface for the ideal scheduler latency. Signed-off-by: Geunsik Lim <geunsik.lim@xxxxxxxxxxx> Acked-by: Hyunjin Choi <hj89.choi@xxxxxxxxxxx> CC: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> CC: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx> CC: Steven Rostedt <rostedt@xxxxxxxxxx> CC: Hugh Dickins <hughd@xxxxxxxxxx> CC: Randy Dunlap <randy.dunlap@xxxxxxxxxx> CC: Ingo Molnar <mingo@xxxxxxx> --- 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@xxxxxxxxx S: Maintained F: mm/memcontrol.c +MEMORY UNMAP OPERATION UNIT INTERFACE +M: Geunsik Lim <geunsik.lim@xxxxxxxxxxx> +S: Maintained +F: mm/munmap_unit_size.c +F: include/linux/munmap_unit_size.h + MEMORY TECHNOLOGY DEVICES (MTD) M: David Woodhouse <dwmw2@xxxxxxxxxxxxx> L: linux-mtd@xxxxxxxxxxxxxxxxxxx -- 1.7.3.4 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. 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: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>