[PATCH] provide means to access the zone from the corresponding chunk

[Paolo Bonzini]

This patch enables the zone collector to recover the page_entry and
alloc_zone structures from the address of an arbitrary ggc_alloc-ed 
pointer.  Unfortunately, while very useful, this is quite invasive.

In order to avoid substantial overhead, it changes the data
representation of the zone allocator so that the page_entry, instead of
being in malloced memory, is simply stored as a header in the page.  For 
small-object pages, you retrieve the page_entry by getting the beginning 
of the pages; for large-object pages, the page_entry is just before the 
chunk.

It also simplifies the way PCH's are written, by embedding the
page_entry struct in the PCH (since it is now a header to the PCH data).
   The PCH zone however is special because it is a single big big
page_entry holding all the objects (both small and large) in the PCH.
For this reason the (unused) type field is changed so that it
distinguishes between objects from the PCH zone and from the other zone.

The patch uses new_persistent_ggc_zone from my patch at
http://gcc.gnu.org/ml/gcc-patches/2004-05/msg00047.html but it can be
checked in independent of that patch simply by changing it to new_ggc_zone.

I can provide a follow-up patch to use this, so that the garbage_zone is 
not scanned.

Bootstrapped/regtested i686-pc-linux-gnu, ok for mainline?

Paolo

2004-05-07  Paolo Bonzini  <bonzini@gnu.org>

	* ggc-common.c (gt_pch_save): Move call to
	ggc_pch_prepare_write after the padding for the mmap-ed
	area has been written.
	* ggc-zone.c (enum object_type): New.
	(alloc_chunk): Make type field a bit wider, and size
	field a bit smaller.
	(page_entry): Add u field to hold a pointer to the first chunk
	or data.  Remove page field.  bytes is not a multiple of the
	page size anymore.	Make the list of entries doubly-linked.
	(PAGE_ENTRY_SIZE): New.
	(pch_zone): New global.
	(ggc_allocated_p): Removed.
	(link_page): New.
	(release_pages): Replace references to page field
	with u.data or u.chunks, carve the page_entry struct
	out of the allocated page and decrement the bytes
	field appropriately.
	(init_ggc): Likewise.
	(sweep_pages): Likewise.
	(check_cookies): Likewise.
	(ggc_collect): Likewise.
	(free_page): Likewise, plus handle doubly-linked list.
	(alloc_small_page): Likewise, plus remove code moved
	to link_page and call it.  Fix head comment.
	(alloc_large_page): Likewise, plus remove code moved
	to link_page and call it.  Fix head comment.
	(ggc_alloc_zone_1): Likewise, plus include zone name into
	the debugging output, and remove code moved to link_page.
	(free_chunk): Likewise, plus include zone name into
	the debugging output.
	(struct ggc_pch_data): Remove ggc_pch_ondisk, we write
	a page_entry.  Move the only field there to the struct.
	Remove the (unused) written field.
	(ggc_pch_count_object): Adjust.
	(ggc_pch_total_size): Adjust and account for the page_entry.
	(ggc_pch_this_base): Account for the space taken by the
	page_entry.
	(ggc_pch_prepare_write): Write a page_entry to disk.
	(ggc_pch_write_object): Remove accesses to the unused
	d->written field.  Set type to OBJ_PCH in the written
	alloc_chunk.
	(ggc_pch_finish): Do not write anything.
	(ggc_pch_read): Link the mmap-ed page_entry in pch_zone.
	Do not create pch_zone here.



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