Struct page entry

概要

• gcc-4.1.0/gcc/ggc-zone.c, gcc-4.1.0/gcc/ggc-page.cにて定義
• 配分ページの状態を記録

実装

ggc-zone.c

• page_entryは、配分ページの状態を記録する。
• これは、全3種類のページの間の一般のデータ(small, large, PCH)。

235 /* A page_entry records the status of an allocation page.  This is the
236    common data between all three kinds of pages - small, large, and
237    PCH.  */
238 typedef struct page_entry
239 {

• 割り当てられたメモリのアドレス

240   /* The address at which the memory is allocated.  */
241   char *page;
242 

• このページエントリが含まれているゾーン

243   /* The zone that this page entry belongs to.  */
244   struct alloc_zone *zone;
245 
246 #ifdef GATHER_STATISTICS

• 生き残っている数

247   /* How many collections we've survived.  */
248   size_t survived;
249 #endif
250 

• このページはsmallオブジェクトに含まれるかlargeオブジェクトに含まれるか

251   /* Does this page contain small objects, or one large object?  */
252   bool large_p;
253 

• ロード済みのPCHの一部か

254   /* Is this page part of the loaded PCH?  */
255   bool pch_p;
256 } page_entry;

ggc-page.c

247 /* A page_entry records the status of an allocation page.  This
248    structure is dynamically sized to fit the bitmap in_use_p.  */
249 typedef struct page_entry
250 {
251   /* The next page-entry with objects of the same size, or NULL if
252      this is the last page-entry.  */
253   struct page_entry *next;
254 
255   /* The previous page-entry with objects of the same size, or NULL if
256      this is the first page-entry.   The PREV pointer exists solely to
257      keep the cost of ggc_free manageable.  */
258   struct page_entry *prev;
259 
260   /* The number of bytes allocated.  (This will always be a multiple
261      of the host system page size.)  */
262   size_t bytes;
263 
264   /* The address at which the memory is allocated.  */
265   char *page;
266 
267 #ifdef USING_MALLOC_PAGE_GROUPS
268   /* Back pointer to the page group this page came from.  */
269   struct page_group *group;
270 #endif
271 
272   /* This is the index in the by_depth varray where this page table
273      can be found.  */
274   unsigned long index_by_depth;
275 
276   /* Context depth of this page.  */
277   unsigned short context_depth;
278 
279   /* The number of free objects remaining on this page.  */
280   unsigned short num_free_objects;
281 
282   /* A likely candidate for the bit position of a free object for the
283      next allocation from this page.  */
284   unsigned short next_bit_hint;
285 
286   /* The lg of size of objects allocated from this page.  */
287   unsigned char order;
288 
289   /* A bit vector indicating whether or not objects are in use.  The
290      Nth bit is one if the Nth object on this page is allocated.  This
291      array is dynamically sized.  */
292   unsigned long in_use_p[1];
293 } page_entry;

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