Red Hat ENTERPRISE LINUX 3 Reference Manual page 93

proc
Chapter 5. The
improve performance on a system using a lot of swap space by telling the kernel to write pages in
large chunks, minimizing the number of disk seeks.
• max_map_count
In most cases, the default value of
— Specifies in megabytes the size of hugepages—large, physically continuous
• hugetlb_pool
memory pages. These pages can be used to create large TLB virtual memory mappings, which are
useful for RAM-intensive database applications. TLB is a special in-CPU cache designed for such
virtual memory mappings.
Although this feature can be adjusted at runtime, it is sensitive to fragmentation issues when grow-
ing the pool while the
essary to place new settings in
Command for information about
sysctl
Refer to
/usr/src/linux-2.4/Documentation/vm/hugetlbpage.txt
tion about configuring hugepages.
Important
Despite being mentioned in
ist within Red Hat Enterprise Linux. Instead
of hugepages available for the system. Also, it is important to remember that
hugepage units, while
• overcommit_memory
cepted or denied. The following three modes are available:
— The kernel performs heuristic memory overcommit handling, by estimating the amount of
0
•
memory available and failing requests that are blatantly invalid. Unfortunately, since memory
is allocated using a heuristic rather than a precise algorithm, this setting can sometimes allow
overloading the memory available on a system. This is the default setting.
— The kernel performs no memory overcommit handling. Under this setting, the potential for
1
•
memory overload is increased, but so is performance for memory intensive tasks (such as those
executed by some scientific software).
— The kernel fails requests for memory that add up to all of swap plus the percent of physi-
2
•
cal RAM specified in
desire less risk of memory overcommitment.
Note
This setting is only recommended for systems with swap areas larger than physical memory.
• overcommit_ratio
/proc/sys/vm/overcommit_memory
— Controls the percentage of total system memory used for page cache. The following
•
pagecache
is a typical output for this file:
1 15
The first value sets the minimum memory to be used as buffer and page cache memory. The middle
value sets the percentage of system memory dedicated to buffer and page cache memory where the
memory management subsystem begins to clear buffer cache more than other kinds of memory to
compensate for a general lack of free memory. The final value specifies the maximum memory to
be used as buffer memory, but is not yet implemented.
File System
— Configures the maximum number of memory map areas a process may have.
65536
field of
MemFree
/etc/sysctl.conf
hugetlbpage.txt
hugetlb_pool
— Configures the conditions under which a large memory request is ac-
/proc/sys/vm/overcommit_ratio
— Specifies the percentage of physical RAM considered when
100
is appropriate.
is low. For this reason, it may be nec-
/proc/meminfo
and reboot. Refer to Section 5.4 Using the
.
sysctl
, the file
/proc/sys/vm/nr_hugepages
should be used to configure the number
hugetlb_pool
configures hugepages in megabytes.
is set to . The default value is
2
for more informa-
nr_hugepages
. This setting is best for those who
.
50
75
does not ex-
uses