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Free large chunks in ggc v2 

This implements the freeing back of large chunks in the ggc madvise path
Richard Guenther asked for.  This way on systems with limited
address space malloc() and other allocators still have
a chance to get back at some of the memory ggc freed. The
fragmented pages are still just given back, but the address space
stays allocated.

I tried freeing only aligned 2MB areas to optimize for 2MB huge
pages, but the hit rate was quite low, so I switched to 1MB+
unaligned areas.

v2: Hardcode free unit size instead of param

gcc/:
2011-10-18  Andi Kleen  <ak@linux.intel.com>

	* ggc-page (release_pages): First free large continuous
	chunks in the madvise path.

From-SVN: r180648
This commit is contained in:
Andi Kleen 2011-10-29 01:01:54 +00:00 committed by Andi Kleen
parent bf72b0094a
commit d33ef9a52b
2 changed files with 53 additions and 0 deletions
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5
gcc/ChangeLog
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@ -1,3 +1,8 @@
2011-10-18 Andi Kleen <ak@linux.intel.com>
* ggc-page (release_pages): First free large continuous
chunks in the madvise path.
2011-10-18 Andi Kleen <ak@linux.intel.com>
* ggc-page.c (alloc_pages): Always round up entry_size.

48
gcc/ggc-page.c
View File

@ -973,6 +973,54 @@ release_pages (void)
page_entry *p, *start_p;
char *start;
size_t len;
size_t mapped_len;
page_entry *next, *prev, *newprev;
size_t free_unit = (GGC_QUIRE_SIZE/2) * G.pagesize;
/* First free larger continuous areas to the OS.
This allows other allocators to grab these areas if needed.
This is only done on larger chunks to avoid fragmentation.
This does not always work because the free_pages list is only
approximately sorted. */
p = G.free_pages;
prev = NULL;
while (p)
{
start = p->page;
start_p = p;
len = 0;
mapped_len = 0;
newprev = prev;
while (p && p->page == start + len)
{
len += p->bytes;
if (!p->discarded)
mapped_len += p->bytes;
newprev = p;
p = p->next;
}
if (len >= free_unit)
{
while (start_p != p)
{
next = start_p->next;
free (start_p);
start_p = next;
}
munmap (start, len);
if (prev)
prev->next = p;
else
G.free_pages = p;
G.bytes_mapped -= mapped_len;
continue;
}
prev = newprev;
}
/* Now give back the fragmented pages to the OS, but keep the address
space to reuse it next time. */
for (p = G.free_pages; p; )
{