47 lines
2.1 KiB
XML
47 lines
2.1 KiB
XML
<?xml version="1.0" encoding='UTF-8'?>
|
|
<!DOCTYPE sect1 PUBLIC "-//OASIS//DTD DocBook V4.5//EN"
|
|
"http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd">
|
|
|
|
<sect1 id="setup-maxmem"><title>Changing Cygwin's Maximum Memory</title>
|
|
|
|
<para>
|
|
Cygwin's heap is extensible. However, it does start out at a fixed size
|
|
and attempts to extend it may run into memory which has been previously
|
|
allocated by Windows. In some cases, this problem can be solved by
|
|
changing a field in the file header which is utilized by Cygwin since
|
|
to keep the initial size of the application heap. If the field contains 0,
|
|
which is the default, the application heap defaults to a size of 384 Megabyte
|
|
on 32 bit Cygwin, 512 Megabyte on 64 bit Cygwin. If the field is set to any
|
|
other value between 4 and 2048, Cygwin tries to reserve as much Megabytes
|
|
for the application heap. The field used for this is the "LoaderFlags" field
|
|
in the NT-specific PE header structure
|
|
(<literal>(IMAGE_NT_HEADER)->OptionalHeader.LoaderFlags</literal>).</para>
|
|
|
|
<para>
|
|
This value can be changed for any executable by using a more recent version
|
|
of the <command>peflags</command> tool from the <literal>rebase</literal>
|
|
Cygwin package. Example:
|
|
|
|
<screen>
|
|
$ peflags --cygwin-heap foo.exe
|
|
foo.exe: initial Cygwin heap size: 0 (0x0) MB
|
|
$ peflags --cygwin-heap=500 foo.exe
|
|
foo.exe: initial Cygwin heap size: 500 (0x1f4) MB
|
|
</screen>
|
|
</para>
|
|
|
|
<para>
|
|
Heap memory can be allocated up to the size of the biggest available free
|
|
block in the processes virtual memory (VM). By default, the VM per process
|
|
is 2 GB for 32 processes. To get more VM for a process, the executable
|
|
must have the "large address aware" flag set in the file header. You can
|
|
use the aforementioned <command>peflags</command> tool to set this flag.
|
|
On 64 bit systems this results in a 4 GB VM for a process started from that
|
|
executable. On 32 bit systems you also have to prepare the system to allow
|
|
up to 3 GB per process. See the Microsoft article
|
|
<ulink url="http://msdn.microsoft.com/en-us/library/bb613473%28VS.85%29.aspx">4-Gigabyte Tuning</ulink>
|
|
for more information.
|
|
</para>
|
|
|
|
</sect1>
|