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gc_md.h
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C/C++ Source or Header
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1998-09-15
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4KB
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101 lines
/*
* @(#)gc_md.h 1.5 98/07/01
*
* Copyright 1995-1998 by Sun Microsystems, Inc.,
* 901 San Antonio Road, Palo Alto, California, 94303, U.S.A.
* All rights reserved.
*
* This software is the confidential and proprietary information
* of Sun Microsystems, Inc. ("Confidential Information"). You
* shall not disclose such Confidential Information and shall use
* it only in accordance with the terms of the license agreement
* you entered into with Sun.
*/
#ifndef _GC_MD_H_
#define _GC_MD_H_
/*---- Win32 defines for garbage collection ----*/
#ifdef DEBUG
/* local debug & error checking flag */
/* #define LDEBUG 1 */
/* Define below if you want lots of verbose info at runtime */
/* #define TRACEGC 1 */
/* define to send strs to debugger (on Mac) */
#undef DPRINTFDEBUG
#endif
#ifdef TRACEGC
/* define below for REALLY detailed print */
#undef TRACEMARK
#undef TRACEFREE
#undef TRACECOMPACT
#undef PDEBUG
#endif
#ifdef PAGED_HEAPS /************ PAGED HEAPS: ********************/
/* In order for the OS to allocate many chunks of aligned memory, leave a little
* room at the end of our chunks that the OS can use for it's own purposes for
* the next allocation.
*/
#define OS_BLOCK_OVERHEAD 0 /* in bytes */
/* On MacOS for instance, sysMemAlign allocates a block that may not be aligned
* and returns an aligned pointer into that block. We may be able to use that
* space, so keep track of it.
*/
#undef WASTED_SPACE_IN_LEADER
/* TUNING ISSUES:
* On machines that don't have a real memalign, WASTED_SPACE_IN_LEADER will be
* true. So chosing a page size is a trade off between wasting up to a page
* per chunk to achive alignment, and using up memory for a large page map.
* Note that a page is the smallest ammount that the gc will request from the
* OS, so it should be reasonable (eg. not 1M on a 4M machine!)
*
* AlignmentWaste(worst) = PAGE_ALIGNMENT / MIN_XXX_PAGES *
* memory used / PAGE_ALIGNMENT;
* = memory used / MIN_XXX_PAGES;
* AlignmentWaste(avg) = memory used / (2 * MIN_XXX_PAGES);
*
* PageMapSize(worst) = address space / PAGE_ALIGNMENT * 8
*
* MITIGATING FACTORS:
* A) The allocator tries to store the mark bits for a chunk in the aligment
* waste area. Note that we need two mark bits for every two words, so:
* MarkBitsSize = memory used / 32;
* There are various round-off issues, but accounting for the savings of
* storing the marks in the waste:
* AlignmentWaste(mitigated_avg) = memory used / (2 * MIN_XXX_PAGES) -
* memory used / 32;
* So, if you keep MIN_XXX_PAGES > 16, AlignmentWaste approaches zero.
*
* B) The page map is only large enough to span the pages handed to us by the
* OS, and it's unlikly that the OS will give us some pages at 0x00000000,
* then a few more pages near 0xFFFFFFFF.
*
* So, keep MIN_XXX_PAGES > 16, maximize PAGE_ALIGNMENT (especially if address
* space is large), but try to keep PAGE_ALIGNMENT * MIN_XXX_PAGES to a
* size that the OS will usually be able to allocate.
*
*/
#define PAGE_ALIGNMENT (64 * 1024) /* page size is the same. */
/* # of bits to shift a pointer to get a page number
* 2 ^ PTR_2_PAGE_SHIFT == PAGE_ALIGNMENT */
#define PTR_2_PAGE_SHIFT (16)
#ifdef LDEBUG /* stress testing */
#define MIN_OBJ_PAGES (2) /* min # of pages to allocate for objects */
#define MIN_HANDLE_PAGES (2) /* min # of pages to allocate for handles */
#else
#define MIN_OBJ_PAGES (32) /* min # of pages to allocate for objects */
#define MIN_HANDLE_PAGES (8) /* min # of pages to allocate for handles */
#endif /* LDEBUG */
#endif /************ END PAGED HEAPS ********************/
#endif /* !_GC_MD_H_ */