Messages in this thread Patch in this message | | | Date | Sat, 19 May 2007 22:36:52 +0200 | From | Eric Dumazet <> | Subject | Re: [PATCH] MM : alloc_large_system_hash() can free some memory for non power-of-two bucketsize |
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David Miller a écrit : > From: Eric Dumazet <dada1@cosmosbay.com> > 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 <dada1@cosmosbay.com> 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); | |