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netfilter: nf_tables: switch trans_elem to real flex array

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When queueing a set element add or removal operation to the transaction
log, check if the previous operation already asks for a the identical
operation on the same set.

If so, store the element reference in the preceding operation.
This significantlty reduces memory consumption when many set add/delete
operations appear in a single transaction.

Example: 10k elements require 937kb of memory (10k allocations from
kmalloc-96 slab).

Assuming we can compact 4 elements in the same set, 468 kbytes
are needed (64 bytes for base struct, nft_trans_elemn, 32 bytes
for nft_trans_one_elem structure, so 2500 allocations from kmalloc-192
slab).

For large batch updates we can compact up to 62 elements
into one single nft_trans_elem structure (~65% mem reduction):
(64 bytes for base struct, nft_trans_elem, 32 byte for nft_trans_one_elem
 struct).

We can halve size of nft_trans_one_elem struct by moving
timeout/expire/update_flags into a dynamically allocated structure,
this allows to store 124 elements in a 2k slab nft_trans_elem struct.
This is done in a followup patch.

Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
This commit is contained in:
Florian Westphal 2024-11-13 16:35:52 +01:00 committed by Pablo Neira Ayuso
parent 466c9b3b2a
commit b0c4946604
1 changed files with 90 additions and 0 deletions
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90
net/netfilter/nf_tables_api.c
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@ -26,6 +26,9 @@
#define NFT_MODULE_AUTOLOAD_LIMIT (MODULE_NAME_LEN - sizeof("nft-expr-255-"))
#define NFT_SET_MAX_ANONLEN 16
/* limit compaction to avoid huge kmalloc/krealloc sizes. */
#define NFT_MAX_SET_NELEMS ((2048 - sizeof(struct nft_trans_elem)) / sizeof(struct nft_trans_one_elem))
unsigned int nf_tables_net_id __read_mostly;
static LIST_HEAD(nf_tables_expressions);
@ -391,6 +394,86 @@ static void nf_tables_unregister_hook(struct net *net,
return __nf_tables_unregister_hook(net, table, chain, false);
}
static bool nft_trans_collapse_set_elem_allowed(const struct nft_trans_elem *a, const struct nft_trans_elem *b)
{
/* NB: the ->bound equality check is defensive, at this time we only merge
* a new nft_trans_elem transaction request with the transaction tail
* element, but a->bound != b->bound would imply a NEWRULE transaction
* is queued in-between.
*
* The set check is mandatory, the NFT_MAX_SET_NELEMS check prevents
* huge krealloc() requests.
*/
return a->set == b->set && a->bound == b->bound && a->nelems < NFT_MAX_SET_NELEMS;
}
static bool nft_trans_collapse_set_elem(struct nftables_pernet *nft_net,
struct nft_trans_elem *tail,
struct nft_trans_elem *trans,
gfp_t gfp)
{
unsigned int nelems, old_nelems = tail->nelems;
struct nft_trans_elem *new_trans;
if (!nft_trans_collapse_set_elem_allowed(tail, trans))
return false;
/* "cannot happen", at this time userspace element add
* requests always allocate a new transaction element.
*
* This serves as a reminder to adjust the list_add_tail
* logic below in case this ever changes.
*/
if (WARN_ON_ONCE(trans->nelems != 1))
return false;
if (check_add_overflow(old_nelems, trans->nelems, &nelems))
return false;
/* krealloc might free tail which invalidates list pointers */
list_del_init(&tail->nft_trans.list);
new_trans = krealloc(tail, struct_size(tail, elems, nelems), gfp);
if (!new_trans) {
list_add_tail(&tail->nft_trans.list, &nft_net->commit_list);
return false;
}
/*
* new_trans->nft_trans.list contains garbage, but
* list_add_tail() doesn't care.
*/
new_trans->nelems = nelems;
new_trans->elems[old_nelems] = trans->elems[0];
list_add_tail(&new_trans->nft_trans.list, &nft_net->commit_list);
return true;
}
static bool nft_trans_try_collapse(struct nftables_pernet *nft_net,
struct nft_trans *trans, gfp_t gfp)
{
struct nft_trans *tail;
if (list_empty(&nft_net->commit_list))
return false;
tail = list_last_entry(&nft_net->commit_list, struct nft_trans, list);
if (tail->msg_type != trans->msg_type)
return false;
switch (trans->msg_type) {
case NFT_MSG_NEWSETELEM:
case NFT_MSG_DELSETELEM:
return nft_trans_collapse_set_elem(nft_net,
nft_trans_container_elem(tail),
nft_trans_container_elem(trans), gfp);
}
return false;
}
static void nft_trans_commit_list_add_tail(struct net *net, struct nft_trans *trans)
{
struct nftables_pernet *nft_net = nft_pernet(net);
@ -424,11 +507,18 @@ static void nft_trans_commit_list_add_tail(struct net *net, struct nft_trans *tr
static void nft_trans_commit_list_add_elem(struct net *net, struct nft_trans *trans,
gfp_t gfp)
{
struct nftables_pernet *nft_net = nft_pernet(net);
WARN_ON_ONCE(trans->msg_type != NFT_MSG_NEWSETELEM &&
trans->msg_type != NFT_MSG_DELSETELEM);
might_alloc(gfp);
if (nft_trans_try_collapse(nft_net, trans, gfp)) {
kfree(trans);
return;
}
nft_trans_commit_list_add_tail(net, trans);
}