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SubjectRe: Memory Problem in 2.4.10-pre2 / __alloc_pages failed
Date
Reposted to include Alex's correction.  Alex, could you please check this?

On September 2, 2001 09:32 pm, Alex Bligh - linux-kernel wrote:
> IDEA: Attempt not to allocate sets of pages buddied with 'nearly
> free' sets of pages.
>
> When freeing pages, we work our way up the orders until
> we find a buddy which is non-empty. Let's assume that
> the free area, and our (non-empty) buddy, are of order N.
> Let's look at whether at order N-1, it's merely half full,
> or completely full. If completely full, we guess that
> the buddy is unlikely to become free soon, and thus
> add our area to the front of the memory queue (mem_add_head)
> else we guess it's more likely to have its buddy freed
> and add it to the back of the memory queue (mem_add_tail).
>
> /Completely/ untested (i.e. uncompiled) patch attached

Rediffed to 2.4.9, whitespace and wrapping problems fixed, and compiled
but not tested. Now we just need a victi^H^H^H^H^H volunteer to try it...
(Stephan?)

--- ../2.4.9.clean/mm/page_alloc.c Thu Aug 16 12:43:02 2001
+++ ./mm/page_alloc.c Sun Sep 2 21:09:05 2001
@@ -69,6 +69,8 @@
struct page *base;
zone_t *zone;

+ int addfront=1;
+
if (page->buffers)
BUG();
if (page->mapping)
@@ -112,10 +114,22 @@
if (area >= zone->free_area + MAX_ORDER)
BUG();
if (!__test_and_change_bit(index, area->map))
- /*
- * the buddy page is still allocated.
- */
- break;
+ {
+ /*
+ * the buddy page is still allocated.
+ *
+ * see how many bits are set in its bitmap;
+ * if 50% or more, we conclude the buddy is
+ * unlikely to be freed soon, and add the
+ * area to the head of the queue; else we
+ * conclude the buddy may be free soon and
+ * add it to the head.
+ */
+ if (mask & 1) /* not order 0 merge */
+ addfront = ( !test_bit((index^1)<<1, (area-1)->map) &&
+ !test_bit(((index^1)<<1) | 1, (area-1)->map) );
+ break;
+ }
/*
* Move the buddy up one level.
*/
@@ -132,7 +146,11 @@
index >>= 1;
page_idx &= mask;
}
- memlist_add_head(&(base + page_idx)->list, &area->free_list);
+
+ if (addfront)
+ memlist_add_head(&(base + page_idx)->list, &area->free_list);
+ else
+ memlist_add_tail(&(base + page_idx)->list, &area->free_list);

spin_unlock_irqrestore(&zone->lock, flags);

-
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