From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Sat, 19 May 2007 01:37:24 -0700 From: Andrew Morton Subject: Re: [PATCH] MM : alloc_large_system_hash() can free some memory for non power-of-two bucketsize Message-Id: <20070519013724.3d4b74e0.akpm@linux-foundation.org> In-Reply-To: <20070518115454.d3e32f4d.dada1@cosmosbay.com> References: <20070518115454.d3e32f4d.dada1@cosmosbay.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org Return-Path: To: Eric Dumazet Cc: "linux-mm@kvack.org" , linux kernel , David Miller List-ID: On Fri, 18 May 2007 11:54:54 +0200 Eric Dumazet wrote: > 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. Watch the 200-column text, please. > 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 > --- > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index ae96dd8..2e0ba08 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -3350,6 +3350,20 @@ 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); > + while (used < alloc_end) { > + free_page(used); > + used += PAGE_SIZE; > + } > + } > } > } while (!table && size > PAGE_SIZE && --log2qty); > It went BUG. static inline int put_page_testzero(struct page *page) { VM_BUG_ON(atomic_read(&page->_count) == 0); return atomic_dec_and_test(&page->_count); } http://userweb.kernel.org/~akpm/s5000523.jpg http://userweb.kernel.org/~akpm/config-vmm.txt -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org