Re: [PATCH] MM : alloc_large_system_hash() can free some memory for non power-of-two bucketsize

[Eric Dumazet <dada1@cosmosbay.com>]

Andrew Morton a écrit :
> 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);
> }
>
> http://userweb.kernel.org/~akpm/s5000523.jpg
> http://userweb.kernel.org/~akpm/config-vmm.txt

I see :(

Maybe David has an idea how this can be done properly ?

ref : http://marc.info/?l=linux-netdev&m=117706074825048&w=2


-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/