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diff --git a/winsup/doc/setup-maxmem.xml b/winsup/doc/setup-maxmem.xml new file mode 100644 index 000000000..1f5ee31a6 --- /dev/null +++ b/winsup/doc/setup-maxmem.xml @@ -0,0 +1,66 @@ +<?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 +version 1.7.10 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. 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> + +<note> +<para> +Older Cygwin releases only supported a global registry setting to +change the initial heap size for all Cygwin processes. This setting is +not used anymore. However, if you're running an older Cygwin release +than 1.7.10, you can add the <literal>DWORD</literal> value +<literal>heap_chunk_in_mb</literal> and set it to the desired memory limit +in decimal MB. You have to stop all Cygwin processes for this setting to +have any effect. It is preferred to do this in Cygwin using the +<command>regtool</command> program included in the Cygwin package. +(see <xref linkend="regtool"></xref>) This example sets the memory limit +to 1024 MB for all Cygwin processes (use HKCU instead of HKLM if you +want to set this only for the current user): + +<screen> +$ regtool -i set /HKLM/Software/Cygwin/heap_chunk_in_mb 1024 +$ regtool -v list /HKLM/Software/Cygwin +</screen> +</para> +</note> + +</sect1> |