NOMMU: Make mmap allocation page trimming behaviour configurable.
NOMMU mmap allocates a piece of memory for an mmap that's rounded up in size to
the nearest power-of-2 number of pages. Currently it then discards the excess
pages back to the page allocator, making that memory available for use by other
things. This can, however, cause greater amount of fragmentation.
To counter this, a sysctl is added in order to fine-tune the trimming
behaviour. The default behaviour remains to trim pages aggressively, while
this can either be disabled completely or set to a higher page-granular
watermark in order to have finer-grained control.
vm region vm_top bits taken from an earlier patch by David Howells.
Signed-off-by: Paul Mundt <lethal@linux-sh.org>
Signed-off-by: David Howells <dhowells@redhat.com>
Tested-by: Mike Frysinger <vapier.adi@gmail.com>
diff --git a/mm/nommu.c b/mm/nommu.c
index 0d363df..a6e8ccf 100644
--- a/mm/nommu.c
+++ b/mm/nommu.c
@@ -10,7 +10,7 @@
* Copyright (c) 2000-2003 David McCullough <davidm@snapgear.com>
* Copyright (c) 2000-2001 D Jeff Dionne <jeff@uClinux.org>
* Copyright (c) 2002 Greg Ungerer <gerg@snapgear.com>
- * Copyright (c) 2007 Paul Mundt <lethal@linux-sh.org>
+ * Copyright (c) 2007-2008 Paul Mundt <lethal@linux-sh.org>
*/
#include <linux/module.h>
@@ -66,6 +66,7 @@
int sysctl_overcommit_memory = OVERCOMMIT_GUESS; /* heuristic overcommit */
int sysctl_overcommit_ratio = 50; /* default is 50% */
int sysctl_max_map_count = DEFAULT_MAX_MAP_COUNT;
+int sysctl_nr_trim_pages = 1; /* page trimming behaviour */
int heap_stack_gap = 0;
atomic_t mmap_pages_allocated;
@@ -455,6 +456,8 @@
last = rb_entry(lastp, struct vm_region, vm_rb);
if (unlikely(last->vm_end <= last->vm_start))
BUG();
+ if (unlikely(last->vm_top < last->vm_end))
+ BUG();
while ((p = rb_next(lastp))) {
region = rb_entry(p, struct vm_region, vm_rb);
@@ -462,7 +465,9 @@
if (unlikely(region->vm_end <= region->vm_start))
BUG();
- if (unlikely(region->vm_start < last->vm_end))
+ if (unlikely(region->vm_top < region->vm_end))
+ BUG();
+ if (unlikely(region->vm_start < last->vm_top))
BUG();
lastp = p;
@@ -536,7 +541,7 @@
/*
* release a reference to a region
* - the caller must hold the region semaphore, which this releases
- * - the region may not have been added to the tree yet, in which case vm_end
+ * - the region may not have been added to the tree yet, in which case vm_top
* will equal vm_start
*/
static void __put_nommu_region(struct vm_region *region)
@@ -547,7 +552,7 @@
BUG_ON(!nommu_region_tree.rb_node);
if (atomic_dec_and_test(®ion->vm_usage)) {
- if (region->vm_end > region->vm_start)
+ if (region->vm_top > region->vm_start)
delete_nommu_region(region);
up_write(&nommu_region_sem);
@@ -558,7 +563,7 @@
* from ramfs/tmpfs mustn't be released here */
if (region->vm_flags & VM_MAPPED_COPY) {
kdebug("free series");
- free_page_series(region->vm_start, region->vm_end);
+ free_page_series(region->vm_start, region->vm_top);
}
kmem_cache_free(vm_region_jar, region);
} else {
@@ -999,6 +1004,10 @@
int ret;
ret = vma->vm_file->f_op->mmap(vma->vm_file, vma);
+ if (ret == 0) {
+ vma->vm_region->vm_top = vma->vm_region->vm_end;
+ return ret;
+ }
if (ret != -ENOSYS)
return ret;
@@ -1027,11 +1036,14 @@
*/
if (vma->vm_file) {
ret = vma->vm_file->f_op->mmap(vma->vm_file, vma);
- if (ret != -ENOSYS) {
+ if (ret == 0) {
/* shouldn't return success if we're not sharing */
- BUG_ON(ret == 0 && !(vma->vm_flags & VM_MAYSHARE));
- return ret; /* success or a real error */
+ BUG_ON(!(vma->vm_flags & VM_MAYSHARE));
+ vma->vm_region->vm_top = vma->vm_region->vm_end;
+ return ret;
}
+ if (ret != -ENOSYS)
+ return ret;
/* getting an ENOSYS error indicates that direct mmap isn't
* possible (as opposed to tried but failed) so we'll try to
@@ -1051,23 +1063,25 @@
if (!pages)
goto enomem;
- /* we allocated a power-of-2 sized page set, so we need to trim off the
- * excess */
total = 1 << order;
atomic_add(total, &mmap_pages_allocated);
point = rlen >> PAGE_SHIFT;
- while (total > point) {
- order = ilog2(total - point);
- n = 1 << order;
- kdebug("shave %lu/%lu @%lu", n, total - point, total);
- atomic_sub(n, &mmap_pages_allocated);
- total -= n;
- set_page_refcounted(pages + total);
- __free_pages(pages + total, order);
+
+ /* we allocated a power-of-2 sized page set, so we may want to trim off
+ * the excess */
+ if (sysctl_nr_trim_pages && total - point >= sysctl_nr_trim_pages) {
+ while (total > point) {
+ order = ilog2(total - point);
+ n = 1 << order;
+ kdebug("shave %lu/%lu @%lu", n, total - point, total);
+ atomic_sub(n, &mmap_pages_allocated);
+ total -= n;
+ set_page_refcounted(pages + total);
+ __free_pages(pages + total, order);
+ }
}
- total = rlen >> PAGE_SHIFT;
for (point = 1; point < total; point++)
set_page_refcounted(&pages[point]);
@@ -1075,6 +1089,7 @@
region->vm_flags = vma->vm_flags |= VM_MAPPED_COPY;
region->vm_start = (unsigned long) base;
region->vm_end = region->vm_start + rlen;
+ region->vm_top = region->vm_start + (total << PAGE_SHIFT);
vma->vm_start = region->vm_start;
vma->vm_end = region->vm_start + len;
@@ -1110,6 +1125,7 @@
free_page_series(region->vm_start, region->vm_end);
region->vm_start = vma->vm_start = 0;
region->vm_end = vma->vm_end = 0;
+ region->vm_top = 0;
return ret;
enomem:
@@ -1401,7 +1417,7 @@
npages = (addr - vma->vm_start) >> PAGE_SHIFT;
if (new_below) {
- region->vm_end = new->vm_end = addr;
+ region->vm_top = region->vm_end = new->vm_end = addr;
} else {
region->vm_start = new->vm_start = addr;
region->vm_pgoff = new->vm_pgoff += npages;
@@ -1418,6 +1434,7 @@
vma->vm_region->vm_pgoff = vma->vm_pgoff += npages;
} else {
vma->vm_region->vm_end = vma->vm_end = addr;
+ vma->vm_region->vm_top = addr;
}
add_nommu_region(vma->vm_region);
add_nommu_region(new->vm_region);
@@ -1454,10 +1471,12 @@
down_write(&nommu_region_sem);
delete_nommu_region(region);
- if (from > region->vm_start)
- region->vm_end = from;
- else
+ if (from > region->vm_start) {
+ to = region->vm_top;
+ region->vm_top = region->vm_end = from;
+ } else {
region->vm_start = to;
+ }
add_nommu_region(region);
up_write(&nommu_region_sem);
