David Miller a écrit :
From: Eric Dumazet <[EMAIL PROTECTED]>
Date: Sat, 19 May 2007 20:07:11 +0200
Maybe David has an idea how this can be done properly ?
ref : http://marc.info/?l=linux-netdev&m=117706074825048&w=2
You need to use __GFP_COMP or similar to make this splitting+freeing
thing work.
Otherwise the individual pages don't have page references, only
the head page of the high-order page will.
Oh thanks David for the hint.
I added a split_page() call and it seems to work now.
[PATCH] 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 <[EMAIL PROTECTED]>
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index ae96dd8..7c219eb 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -3350,6 +3350,21 @@ void *__init alloc_large_system_hash(const char
*tablename,
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);
