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SubjectRe: [RFC] tree-based bootmem
On Sat, Nov 17, 2001 at 01:14:15AM -0800, William Lee Irwin III wrote:
> This is a repost including some corrections of a bootmem allocator that
> tracks ranges explicitly, and uses segment trees to assist in searching
> for available memory. Perhaps it is even a new version. Some prior
> reports indicated mail headers were munged, preventing replies and some
> people from seeing it at all.

Some more corrections are needed, and many thanks to Russell King for
assisting me in finding them, and for providing access to a system in
order to debug these issues.

(1) prevent integer overflow in FEASIBLE()
(2) prevent integer overflow in ENDS_ABOVE()
(3) test for !segment_contains_point(optimum, goal)
in __alloc_bootmem_core() as an additional condition under
which the the goal should be discounted as a possible starting
address for the returned interval. The symptom seen without
the test is an interval that wraps around ULONG_MAX


This patch tested on ARM.


Cheers,
Bill


--- linux/mm/bootmem.c Sun Nov 18 23:42:26 2001
+++ linux-arm/mm/bootmem.c Wed Nov 21 07:58:25 2001
@@ -462,14 +440,18 @@
* that is not sufficient because of alignment constraints.
*/

-#define FEASIBLE(seg, len, align) \
- ((RND_UP(segment_start(seg), align) + (len) - 1) <= segment_end(seg))
+#define FEASIBLE(seg, len, align) \
+( \
+ (segment_end(seg) >= RND_UP(segment_start(seg), align)) \
+ && \
+ ((segment_end(seg) - RND_UP(segment_start(seg), align)) > (len))\
+)

#define STARTS_BELOW(seg,goal,align,len) \
(RND_UP(segment_start(seg), align) <= (goal))

#define ENDS_ABOVE(seg, goal, align, len) \
- (segment_end(seg) > ((goal) + (len)))
+ ((segment_end(seg) > (goal)) && ((segment_end(seg) - (goal)) > (len)))

#define GOAL_WITHIN(seg,goal,align,len) \
(STARTS_BELOW(seg,goal,align,len) && ENDS_ABOVE(seg,goal,align,len))
@@ -635,7 +608,9 @@

segment_set_endpoints(&reserved, goal, goal + length - 1);

- if(!segment_contains(optimum, &reserved))
+ if(!segment_contains_point(optimum, goal)
+ || !segment_contains(optimum, &reserved))
+
segment_set_endpoints(&reserved,
RND_UP(segment_start(optimum), align),
RND_UP(segment_start(optimum),align)+length-1);
-
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