Stephen Hemminger writes:
> Eric wisely pointed out that for larger sizes of nodes, the
> current allocation in fib_trie wastes lots of memory. For a sample
> of routes extracted from the bugzilla bug the largest node grows
> to 2M bytes on 64 bit system. This leads to 2044K of wasted memory.
>
> There are two possible solutions (see attached). One uses vmalloc()
> rather than alloc_pages, but has to add complexity on freeing.
> The other adds a layer of indirection to the tnode lookup.
>
> Both have been tested on net-2.6.26 with the huge route table.
> I slightly prefer the vmalloc version, but both work fine.
Do we get slower with vmalloc due to TLB-lookups etc? Guess this
should be investigated.
http://mail.nl.linux.org/kernelnewbies/2005-12/msg00212.html
Memory savings (different)
Cheers
--ro
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Total size: 7841 kB
>
> IPV4: fib_trie use vmalloc for large tnodes
>
> Use vmalloc rather than alloc_pages to avoid wasting memory.
> The problem is that tnode structure has a power of 2 sized array,
> plus a header. So the current code wastes almost half the memory
> allocated because it always needs the next bigger size to hold
> that small header.
>
> This is similar to an earlier patch by Eric, but instead of a list
> and lock, I used a workqueue to handle the fact that vfree can't
> be done in interrupt context.
>
> Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
>
> ---
> net/ipv4/fib_trie.c | 25 +++++++++++++++----------
> 1 file changed, 15 insertions(+), 10 deletions(-)
>
> --- a/net/ipv4/fib_trie.c 2008-04-04 08:57:01.000000000 -0700
> +++ b/net/ipv4/fib_trie.c 2008-04-04 08:57:03.000000000 -0700
> @@ -122,7 +122,10 @@ struct tnode {
> unsigned char bits; /* 2log(KEYLENGTH) bits needed */
> unsigned int full_children; /* KEYLENGTH bits needed */
> unsigned int empty_children; /* KEYLENGTH bits needed */
> - struct rcu_head rcu;
> + union {
> + struct rcu_head rcu;
> + struct work_struct work;
> + };
> struct node *child[0];
> };
>
> @@ -350,16 +353,16 @@ static inline void free_leaf_info(struct
>
> static struct tnode *tnode_alloc(size_t size)
> {
> - struct page *pages;
> -
> if (size <= PAGE_SIZE)
> return kzalloc(size, GFP_KERNEL);
> + else
> + return __vmalloc(size, GFP_KERNEL | __GFP_ZERO, PAGE_KERNEL);
> +}
>
> - pages = alloc_pages(GFP_KERNEL|__GFP_ZERO, get_order(size));
> - if (!pages)
> - return NULL;
> -
> - return page_address(pages);
> +static void __tnode_vfree(struct work_struct *arg)
> +{
> + struct tnode *tn = container_of(arg, struct tnode, work);
> + vfree(tn);
> }
>
> static void __tnode_free_rcu(struct rcu_head *head)
> @@ -370,8 +373,10 @@ static void __tnode_free_rcu(struct rcu_
>
> if (size <= PAGE_SIZE)
> kfree(tn);
> - else
> - free_pages((unsigned long)tn, get_order(size));
> + else {
> + INIT_WORK(&tn->work, __tnode_vfree);
> + schedule_work(&tn->work);
> + }
> }
>
> static inline void tnode_free(struct tnode *tn)
> IPV4: fib_trie split child off from tnode
>
> For large tnode's the power of 2 allocation wastes almost half the space
> since the tnode is allocated with the power of 2 sized child pointers.
> To solve this add a layer of indirection. For small nodes (the common case)
> can just use a single allocation, for larger use pages like before.
>
> Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
>
>
> ---
> net/ipv4/fib_trie.c | 43 ++++++++++++++++++++++++++-----------------
> 1 file changed, 26 insertions(+), 17 deletions(-)
>
> --- a/net/ipv4/fib_trie.c 2008-04-03 09:09:45.000000000 -0700
> +++ b/net/ipv4/fib_trie.c 2008-04-03 22:08:33.000000000 -0700
> @@ -120,10 +120,10 @@ struct tnode {
> t_key key;
> unsigned char pos; /* 2log(KEYLENGTH) bits needed */
> unsigned char bits; /* 2log(KEYLENGTH) bits needed */
> + struct node **child;
> unsigned int full_children; /* KEYLENGTH bits needed */
> unsigned int empty_children; /* KEYLENGTH bits needed */
> struct rcu_head rcu;
> - struct node *child[0];
> };
>
> #ifdef CONFIG_IP_FIB_TRIE_STATS
> @@ -348,30 +348,40 @@ static inline void free_leaf_info(struct
> call_rcu(&leaf->rcu, __leaf_info_free_rcu);
> }
>
> -static struct tnode *tnode_alloc(size_t size)
> +static struct tnode *tnode_alloc(int bits)
> {
> - struct page *pages;
> -
> - if (size <= PAGE_SIZE)
> - return kzalloc(size, GFP_KERNEL);
> + size_t space = sizeof(struct node *) << bits;
> + size_t size = space + sizeof(struct tnode);
> + struct tnode *tn;
>
> - pages = alloc_pages(GFP_KERNEL|__GFP_ZERO, get_order(size));
> - if (!pages)
> + tn = kzalloc(size > PAGE_SIZE ? sizeof(struct tnode) : size, GFP_KERNEL);
> + if (!tn)
> return NULL;
>
> - return page_address(pages);
> + if (size <= PAGE_SIZE)
> + tn->child = (struct node **) (tn + 1);
> + else {
> + struct page *pages = alloc_pages(GFP_KERNEL|__GFP_ZERO,
> + get_order(space));
> + if (!pages) {
> + kfree(tn);
> + return NULL;
> + }
> + tn->child = page_address(pages);
> + }
> +
> + return tn;
> }
>
> static void __tnode_free_rcu(struct rcu_head *head)
> {
> struct tnode *tn = container_of(head, struct tnode, rcu);
> - size_t size = sizeof(struct tnode) +
> - (sizeof(struct node *) << tn->bits);
> + size_t space = sizeof(struct node *) << tn->bits;
> + size_t size = space + sizeof(struct tnode);
>
> - if (size <= PAGE_SIZE)
> - kfree(tn);
> - else
> - free_pages((unsigned long)tn, get_order(size));
> + if (size > PAGE_SIZE)
> + free_pages((unsigned long)tn->child, get_order(space));
> + kfree(tn);
> }
>
> static inline void tnode_free(struct tnode *tn)
> @@ -404,8 +414,7 @@ static struct leaf_info *leaf_info_new(i
>
> static struct tnode *tnode_new(t_key key, int pos, int bits)
> {
> - size_t sz = sizeof(struct tnode) + (sizeof(struct node *) << bits);
> - struct tnode *tn = tnode_alloc(sz);
> + struct tnode *tn = tnode_alloc(bits);
>
> if (tn) {
> tn->parent = T_TNODE;
--
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