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diff --git a/sag-0.6.1-www/Invisible/sag-0.6/node61.html b/sag-0.6.1-www/Invisible/sag-0.6/node61.html new file mode 100644 index 0000000..5385417 --- /dev/null +++ b/sag-0.6.1-www/Invisible/sag-0.6/node61.html @@ -0,0 +1,93 @@ +<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0//EN"> +<!--Converted with LaTeX2HTML 96.1-h (September 30, 1996) by Nikos Drakos (nikos@cbl.leeds.ac.uk), CBLU, University of Leeds --> +<HTML> +<HEAD> +<TITLE>Creating a swap space</TITLE> +<META NAME="description" CONTENT="Creating a swap space"> +<META NAME="keywords" CONTENT="sag"> +<META NAME="resource-type" CONTENT="document"> +<META NAME="distribution" CONTENT="global"> +<LINK REL=STYLESHEET HREF="sag.css"> +</HEAD> +<BODY LANG="EN" > + <A NAME="tex2html1082" HREF="node62.html"><IMG WIDTH=37 HEIGHT=24 ALIGN=BOTTOM ALT="next" SRC="./next_motif.gif"></A> <A NAME="tex2html1080" HREF="node59.html"><IMG WIDTH=26 HEIGHT=24 ALIGN=BOTTOM ALT="up" SRC="./up_motif.gif"></A> <A NAME="tex2html1074" HREF="node60.html"><IMG WIDTH=63 HEIGHT=24 ALIGN=BOTTOM ALT="previous" SRC="./previous_motif.gif"></A> <A NAME="tex2html1084" HREF="node1.html"><IMG WIDTH=65 HEIGHT=24 ALIGN=BOTTOM ALT="contents" SRC="./contents_motif.gif"></A> <A NAME="tex2html1085" HREF="node114.html"><IMG WIDTH=43 HEIGHT=24 ALIGN=BOTTOM ALT="index" SRC="./index_motif.gif"></A> <BR> +<B> Next:</B> <A NAME="tex2html1083" HREF="node62.html">Using a swap space</A> +<B>Up:</B> <A NAME="tex2html1081" HREF="node59.html">Memory Management</A> +<B> Previous:</B> <A NAME="tex2html1075" HREF="node60.html">What is virtual memory?</A> +<BR> <P> +<H1><A NAME="SECTION00620000000000000000">Creating a swap space</A></H1> +<P> + A swap file is an ordinary file; it is in no way special to + the kernel. The only thing that matters to the kernel is that + it has no holes, and that it is prepared for use with + <tt>mkswap</tt><A NAME="1891"> </A>. It must reside on a local disk, however; it + can't reside in a filesystem that has been mounted over NFS + due to implementation reasons. +<P> + The bit about holes is important. The swap file + reserves the disk space so that the kernel can quickly swap out + a page without having to go through all the things + that are necessary when allocating a disk sector to a file. + The kernel merely uses any sectors that have already been + allocated to the file. Because a hole in a file means that + there are no disk sectors allocated (for that place in the + file), it is not good for the kernel to try to use them. +<P> + One good way to create the swap file without holes is through + the following command: + <BLOCKQUOTE> <TT> +<code>$</code> <I>dd if=/dev/zero of=/extra-swap bs=1024 count=1024</I><BR> +<code>1024+0 records in</code> <BR> +<code>1024+0 records out</code> <BR> +<code>$</code> + </TT></BLOCKQUOTE> + where <tt>/extra-swap</tt><A NAME="1893"> </A> is the name of the swap file and + the size of is given after the <tt>count=</tt>. It is best for + the size to be a multiple of 4, because the kernel writes out + <b>memory pages</b>, which are 4 kilobytes in size. If the + size is not a multiple of 4, the last couple of kilobytes may + be unused. +<P> + A swap partition is also not special in any way. You create it + just like any other partition; the only difference is that it is + used as a raw partition, that is, it will not contain any + filesystem at all. It is a good idea to mark swap partitions as + type 82 (Linux swap); this will the make partition listings + clearer, even though it is not strictly necessary to the kernel. +<P> + After you have created a swap file or a swap partition, you + need to write a signature to its beginning; this contains some + administrative information and is used by the kernel. The + command to do this is <tt>mkswap</tt><A NAME="1896"> </A>, used like this: + <BLOCKQUOTE> <TT> +<code>$</code> <I>mkswap /extra-swap 1024</I> <BR> +<code>Setting up swapspace, size = 1044480 bytes</code> <BR> +<code>$</code> + </TT></BLOCKQUOTE> + Note that the swap space is still not in use yet: it + exists, but the kernel does not use it to provide virtual + memory. +<P> + You should be very careful when using <tt>mkswap</tt><A NAME="1898"> </A>, since it + does not check that the file or partition isn't used for anything + else. <em>You can easily overwrite important files and + partitions with <tt>mkswap</tt><A NAME="1900"> </A>!</em> Fortunately, you should only + need to use <tt>mkswap</tt><A NAME="1902"> </A> when you install your system. +<P> + The Linux memory manager limits the size of each swap space to + about 127 MB (for various technical reasons, the actual limit + is <IMG WIDTH=78 HEIGHT=12 ALIGN=MIDDLE ALT="tex2html_wrap_inline4269" SRC="img11.gif"> bytes, or + 127.6875 megabytes). You can, however, use up to + 16 swap spaces simultaneously, for a total of almost + 2 GB.<A NAME="tex2html27" HREF="footnode.html#1836"><IMG ALIGN=BOTTOM ALT="gif" SRC="./foot_motif.gif"></A> +<P> +<HR><A NAME="tex2html1082" HREF="node62.html"><IMG WIDTH=37 HEIGHT=24 ALIGN=BOTTOM ALT="next" SRC="./next_motif.gif"></A> <A NAME="tex2html1080" HREF="node59.html"><IMG WIDTH=26 HEIGHT=24 ALIGN=BOTTOM ALT="up" SRC="./up_motif.gif"></A> <A NAME="tex2html1074" HREF="node60.html"><IMG WIDTH=63 HEIGHT=24 ALIGN=BOTTOM ALT="previous" SRC="./previous_motif.gif"></A> <A NAME="tex2html1084" HREF="node1.html"><IMG WIDTH=65 HEIGHT=24 ALIGN=BOTTOM ALT="contents" SRC="./contents_motif.gif"></A> <A NAME="tex2html1085" HREF="node114.html"><IMG WIDTH=43 HEIGHT=24 ALIGN=BOTTOM ALT="index" SRC="./index_motif.gif"></A> <BR> +<B> Next:</B> <A NAME="tex2html1083" HREF="node62.html">Using a swap space</A> +<B>Up:</B> <A NAME="tex2html1081" HREF="node59.html">Memory Management</A> +<B> Previous:</B> <A NAME="tex2html1075" HREF="node60.html">What is virtual memory?</A> +<P><ADDRESS> +<I>Lars Wirzenius <BR> +Sat Nov 15 02:32:11 EET 1997</I> +</ADDRESS> +</BODY> +</HTML> |