Allocate backwards, ready for metadata.

[ccan] / alloc / alloc.c

diff --git a/alloc/alloc.c b/alloc/alloc.c
index f3638340949fedc9187c68e8567af73489cbf318..3ec6952c82c8b6d20187ea722d56a907d518548f 100644 (file)
--- a/alloc/alloc.c
+++ b/alloc/alloc.c
@@ -48,7 +48,8 @@ static unsigned long metadata_length(void *pool, unsigned long poolsize)
 void *alloc_get(void *pool, unsigned long poolsize,
                unsigned long size, unsigned long align)
 {
-       unsigned long i, free, want, metalen;
+       long i;
+       unsigned long free, want, metalen;
 
        if (poolsize < MIN_SIZE)
                return NULL;
@@ -61,20 +62,22 @@ void *alloc_get(void *pool, unsigned long poolsize,
        metalen = metadata_length(pool, poolsize);
 
        free = 0;
-       for (i = 0; i < (poolsize - metalen) / getpagesize(); i++) {
+       /* We allocate from far end, to increase ability to expand metadata. */
+       for (i = (poolsize - metalen) / getpagesize() - 1; i >= 0; i--) {
                switch (get_page_state(pool, i)) {
                case FREE:
                        if (++free >= want) {
-                               unsigned int j;
+                               unsigned long j;
                                char *ret = (char *)pool + metalen
-                                       + (i - want + 1) * getpagesize();
+                                       + i * getpagesize();
 
+                               /* They might ask for multi-page alignment. */
                                if ((unsigned long)ret % align)
                                        continue;
 
-                               for (j = i; j > i - want + 1; j--)
+                               for (j = i+1; j < i + want; j++)
                                        set_page_state(pool, j, TAKEN);
-                               set_page_state(pool, i - want + 1, TAKEN_START);
+                               set_page_state(pool, i, TAKEN_START);
                                return ret;
                        }
                        break;