MM: alloc_large_system_hash() can free some memory for non power-of-two bucketsize
alloc_large_system_hash() is called at boot time to allocate space for
several large hash tables.
Lately, TCP hash table was changed and its bucketsize is not a power-of-two
anymore.
On most setups, alloc_large_system_hash() allocates one big page (order >
0) with __get_free_pages(GFP_ATOMIC, order). This single high_order page
has a power-of-two size, bigger than the needed size.
We can free all pages that wont be used by the hash table.
On a 1GB i386 machine, this patch saves 128 KB of LOWMEM memory.
TCP established hash table entries: 32768 (order: 6, 393216 bytes)
Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 092b2d8..8dadda6 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3584,6 +3584,21 @@
for (order = 0; ((1UL << order) << PAGE_SHIFT) < size; order++)
;
table = (void*) __get_free_pages(GFP_ATOMIC, order);
+ /*
+ * If bucketsize is not a power-of-two, we may free
+ * some pages at the end of hash table.
+ */
+ if (table) {
+ unsigned long alloc_end = (unsigned long)table +
+ (PAGE_SIZE << order);
+ unsigned long used = (unsigned long)table +
+ PAGE_ALIGN(size);
+ split_page(virt_to_page(table), order);
+ while (used < alloc_end) {
+ free_page(used);
+ used += PAGE_SIZE;
+ }
+ }
}
} while (!table && size > PAGE_SIZE && --log2qty);