Messages in this thread | | | 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 |
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On Fri, 18 May 2007 11:54:54 +0200 Eric Dumazet <dada1@cosmosbay.com> 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 <dada1@cosmosbay.com> > --- > 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); }
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