82 lines
2 KiB
Plaintext
82 lines
2 KiB
Plaintext
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.TH XALLOC 9
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.SH NAME
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xalloc, xallocz, xspanalloc, xfree, xsummary \- basic memory management
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.SH SYNOPSIS
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.ta \w'\fLvoid* 'u
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.B
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void* xalloc(ulong size)
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.PP
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.B
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void* xallocz(ulong size, int clr)
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.PP
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.B
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void* xspanalloc(ulong size, int align, ulong span)
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.PP
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.B
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void xfree(void *p)
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.PP
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.B
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void xsummary(void)
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.SH DESCRIPTION
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These are primitives used by higher-level memory allocators in the kernel,
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such as
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.IR malloc (9).
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They are not intended for use directly by most kernel routines.
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The main exceptions are routines that permanently allocate large structures,
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or need the special alignment properties guaranteed by
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.IR xspanalloc .
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.PP
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.I Xalloc
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returns a pointer to a range of size bytes of memory. The memory will be zero filled and aligned on a 8 byte
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.RB ( BY2V )
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address. If the memory is not available,
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.B xalloc
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returns a null pointer.
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.PP
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.I Xmallocz
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will clear the memory after allocation if
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.I clr
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is set to a value other than zero. Since it is used by
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.IR xmalloc ,
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the same diagnostics apply.
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.PP
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.I Xspanalloc
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allocates memory given alignment and spanning constraints.
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The block returned will contain
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.I size
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bytes, aligned on a boundary that is
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.BI "0 mod" " align,"
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in such a way that the memory in the block does not
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span an address that is
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.BI "0 mod" " span."
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.I Xspanalloc
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is intended for use
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allocating hardware data structures (eg, page tables) or I/O buffers
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that must satisfy specific alignment restrictions.
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If
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.I xspanalloc
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cannot allocate memory to satisfy the given constraints, it will
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.IR panic (9).
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The technique it uses can sometimes cause memory to be wasted.
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Consequently,
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.I xspanalloc
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should be used sparingly.
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.PP
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.I Xfree
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frees the block of memory at
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.IR p ,
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which must be an address previously returned by
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.I xalloc
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(not
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.IR xspanalloc ).
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.PP
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.I Xsummary
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dumps memory allocation statistics to the console.
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The output includes the total free space, the number of free holes,
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and a summary of active holes.
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Each line shows `address top size'.
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.SH SOURCE
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.B /sys/src/9/port/xalloc.c
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.SH SEE ALSO
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.IR malloc (9)
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