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Subject[PATCH 4/4] munmap: documentation of munmap operation interface
Date
From: Geunsik Lim <geunsik.lim@samsung.com>

kernel documentation to utilize flexible memory unmap operation
interface for the ideal scheduler latency.

Signed-off-by: Geunsik Lim <geunsik.lim@samsung.com>
Acked-by: Hyunjin Choi <hj89.choi@samsung.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@kvack.org
S: Maintained
F: mm/memcontrol.c

+MEMORY UNMAP OPERATION UNIT INTERFACE
+M: Geunsik Lim <geunsik.lim@samsung.com>
+L: linux-rt-users@vger.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@infradead.org>
L: linux-mtd@lists.infradead.org
--
1.7.3.4


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