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Date: Fri, 11 Feb 2022 19:42:33 +0000
From: Song Liu <songliubraving@...com>
To: Daniel Borkmann <daniel@...earbox.net>
CC: Song Liu <song@...nel.org>,
Linux Memory Management List <linux-mm@...ck.org>,
bpf <bpf@...r.kernel.org>,
Network Development <netdev@...r.kernel.org>,
Alexei Starovoitov <ast@...nel.org>,
"Andrii Nakryiko" <andrii@...nel.org>,
Kernel Team <Kernel-team@...com>,
Andrew Morton <akpm@...ux-foundation.org>,
Eric Dumazet <eric.dumazet@...il.com>,
"Michal Hocko" <mhocko@...e.com>
Subject: Re: [PATCH bpf-next 2/2] bpf: flexible size for bpf_prog_pack
> On Feb 11, 2022, at 6:35 AM, Daniel Borkmann <daniel@...earbox.net> wrote:
>
> On 2/10/22 5:51 PM, Song Liu wrote:
>>> On Feb 10, 2022, at 12:25 AM, Daniel Borkmann <daniel@...earbox.net> wrote:
>>> On 2/10/22 7:41 AM, Song Liu wrote:
>>>> bpf_prog_pack uses huge pages to reduce pressue on instruction TLB.
>>>> To guarantee allocating huge pages for bpf_prog_pack, it is necessary to
>>>> allocate memory of size PMD_SIZE * num_online_nodes().
>>>> On the other hand, if the system doesn't support huge pages, it is more
>>>> efficient to allocate PAGE_SIZE bpf_prog_pack.
>>>> Address different scenarios with more flexible bpf_prog_pack_size().
>>>> Signed-off-by: Song Liu <song@...nel.org>
>>>> ---
>>>> kernel/bpf/core.c | 47 +++++++++++++++++++++++++++--------------------
>>>> 1 file changed, 27 insertions(+), 20 deletions(-)
>>>> diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
>>>> index 42d96549a804..d961a1f07a13 100644
>>>> --- a/kernel/bpf/core.c
>>>> +++ b/kernel/bpf/core.c
>>>> @@ -814,46 +814,53 @@ int bpf_jit_add_poke_descriptor(struct bpf_prog *prog,
>>>> * allocator. The prog_pack allocator uses HPAGE_PMD_SIZE page (2MB on x86)
>>>> * to host BPF programs.
>>>> */
>>>> -#ifdef CONFIG_TRANSPARENT_HUGEPAGE
>>>> -#define BPF_PROG_PACK_SIZE HPAGE_PMD_SIZE
>>>> -#else
>>>> -#define BPF_PROG_PACK_SIZE PAGE_SIZE
>>>> -#endif
>>>> #define BPF_PROG_CHUNK_SHIFT 6
>>>> #define BPF_PROG_CHUNK_SIZE (1 << BPF_PROG_CHUNK_SHIFT)
>>>> #define BPF_PROG_CHUNK_MASK (~(BPF_PROG_CHUNK_SIZE - 1))
>>>> -#define BPF_PROG_CHUNK_COUNT (BPF_PROG_PACK_SIZE / BPF_PROG_CHUNK_SIZE)
>>>> struct bpf_prog_pack {
>>>> struct list_head list;
>>>> void *ptr;
>>>> - unsigned long bitmap[BITS_TO_LONGS(BPF_PROG_CHUNK_COUNT)];
>>>> + unsigned long bitmap[];
>>>> };
>>>> -#define BPF_PROG_MAX_PACK_PROG_SIZE BPF_PROG_PACK_SIZE
>>>> #define BPF_PROG_SIZE_TO_NBITS(size) (round_up(size, BPF_PROG_CHUNK_SIZE) / BPF_PROG_CHUNK_SIZE)
>>>> static DEFINE_MUTEX(pack_mutex);
>>>> static LIST_HEAD(pack_list);
>>>> +static inline int bpf_prog_pack_size(void)
>>>> +{
>>>> + /* If vmap_allow_huge == true, use pack size of the smallest
>>>> + * possible vmalloc huge page: PMD_SIZE * num_online_nodes().
>>>> + * Otherwise, use pack size of PAGE_SIZE.
>>>> + */
>>>> + return get_vmap_allow_huge() ? PMD_SIZE * num_online_nodes() : PAGE_SIZE;
>>>> +}
>>>
>>> Imho, this is making too many assumptions about implementation details. Can't we
>>> just add a new module_alloc*() API instead which internally guarantees allocating
>>> huge pages when enabled/supported (e.g. with a __weak function as fallback)?
>> I agree that this is making too many assumptions. But a new module_alloc_huge()
>> may not work, because we need the caller to know the proper size to ask for.
>> (Or maybe I misunderstood your suggestion?)
>> How about we introduce something like
>> /* minimal size to get huge pages from vmalloc. If not possible,
>> * return 0 (or -1?)
>> */
>> int vmalloc_hpage_min_size(void)
>> {
>> return vmap_allow_huge ? PMD_SIZE * num_online_nodes() : 0;
>> }
>
> And that would live inside mm/vmalloc.c and is exported to users ...
Yeah, this will go to vmalloc.c.
>
>> /* minimal size to get huge pages from module_alloc */
>> int module_alloc_hpage_min_size(void)
>> {
>> return vmalloc_hpage_min_size();
>> }
>
> ... and this one as wrapper in module alloc infra with __weak attr?
And this goes to some module.c file(s). I am not quite sure whether we
need __weak attr or not.
>
>> static inline int bpf_prog_pack_size(void)
>> {
>> return module_alloc_hpage_min_size() ? : PAGE_SIZE;
>> }
>
> Could probably work. It's not nice, but at least in the corresponding places so it's
> not exposed / hard coded inside bpf and assuming implementation details which could
> potentially break later on.
I don't really like it either.
Another way to do this is to test the required size for bpf_prog_pack
in BPF code, something like the following. The pro of this version is
that we don't need changes in vmalloc and module code.
Thanks,
Song
diff --git i/kernel/bpf/core.c w/kernel/bpf/core.c
index 44623c9b5bb1..3cfd0f0c93d2 100644
--- i/kernel/bpf/core.c
+++ w/kernel/bpf/core.c
@@ -814,15 +814,9 @@ int bpf_jit_add_poke_descriptor(struct bpf_prog *prog,
* allocator. The prog_pack allocator uses HPAGE_PMD_SIZE page (2MB on x86)
* to host BPF programs.
*/
-#ifdef CONFIG_TRANSPARENT_HUGEPAGE
-#define BPF_PROG_PACK_SIZE HPAGE_PMD_SIZE
-#else
-#define BPF_PROG_PACK_SIZE PAGE_SIZE
-#endif
#define BPF_PROG_CHUNK_SHIFT 6
#define BPF_PROG_CHUNK_SIZE (1 << BPF_PROG_CHUNK_SHIFT)
#define BPF_PROG_CHUNK_MASK (~(BPF_PROG_CHUNK_SIZE - 1))
-#define BPF_PROG_CHUNK_COUNT (BPF_PROG_PACK_SIZE / BPF_PROG_CHUNK_SIZE)
struct bpf_prog_pack {
struct list_head list;
@@ -830,30 +824,56 @@ struct bpf_prog_pack {
unsigned long bitmap[];
};
-#define BPF_PROG_MAX_PACK_PROG_SIZE BPF_PROG_PACK_SIZE
#define BPF_PROG_SIZE_TO_NBITS(size) (round_up(size, BPF_PROG_CHUNK_SIZE) / BPF_PROG_CHUNK_SIZE)
+static int bpf_prog_pack_size = -1;
+
+static inline int bpf_prog_chunk_count(void)
+{
+ WARN_ON_ONCE(bpf_prog_pack_size == -1);
+ return bpf_prog_pack_size / BPF_PROG_CHUNK_SIZE;
+}
+
static DEFINE_MUTEX(pack_mutex);
static LIST_HEAD(pack_list);
static struct bpf_prog_pack *alloc_new_pack(void)
{
struct bpf_prog_pack *pack;
+ void *ptr;
+ int size;
- pack = kzalloc(sizeof(*pack) + BITS_TO_BYTES(BPF_PROG_CHUNK_COUNT), GFP_KERNEL);
- if (!pack)
+ /* Test whether we can get huge pages. If not just use PAGE_SIZE
+ * packs.
+ */
+ if (bpf_prog_pack_size == -1) {
+ size = PMD_SIZE * num_online_nodes();
+ ptr = module_alloc(size);
+ if (is_vm_area_hugepages(ptr)) {
+ bpf_prog_pack_size = size;
+ goto got_ptr;
+ } else {
+ bpf_prog_pack_size = PAGE_SIZE;
+ vfree(ptr);
+ }
+ }
+
+ ptr = module_alloc(bpf_prog_pack_size);
+ if (!ptr)
return NULL;
- pack->ptr = module_alloc(BPF_PROG_PACK_SIZE);
- if (!pack->ptr) {
- kfree(pack);
+got_ptr:
+ pack = kzalloc(sizeof(*pack) + BITS_TO_BYTES(bpf_prog_chunk_count()), GFP_KERNEL);
+ if (!pack) {
+ vfree(ptr);
return NULL;
}
- bitmap_zero(pack->bitmap, BPF_PROG_PACK_SIZE / BPF_PROG_CHUNK_SIZE);
+ pack->ptr = ptr;
+ bitmap_zero(pack->bitmap, bpf_prog_pack_size / BPF_PROG_CHUNK_SIZE);
list_add_tail(&pack->list, &pack_list);
set_vm_flush_reset_perms(pack->ptr);
- set_memory_ro((unsigned long)pack->ptr, BPF_PROG_PACK_SIZE / PAGE_SIZE);
- set_memory_x((unsigned long)pack->ptr, BPF_PROG_PACK_SIZE / PAGE_SIZE);
+ set_memory_ro((unsigned long)pack->ptr, bpf_prog_pack_size / PAGE_SIZE);
+ set_memory_x((unsigned long)pack->ptr, bpf_prog_pack_size / PAGE_SIZE);
return pack;
}
@@ -864,7 +884,7 @@ static void *bpf_prog_pack_alloc(u32 size)
unsigned long pos;
void *ptr = NULL;
- if (size > BPF_PROG_MAX_PACK_PROG_SIZE) {
+ if (size > bpf_prog_pack_size) {
size = round_up(size, PAGE_SIZE);
ptr = module_alloc(size);
if (ptr) {
@@ -876,9 +896,9 @@ static void *bpf_prog_pack_alloc(u32 size)
}
mutex_lock(&pack_mutex);
list_for_each_entry(pack, &pack_list, list) {
- pos = bitmap_find_next_zero_area(pack->bitmap, BPF_PROG_CHUNK_COUNT, 0,
+ pos = bitmap_find_next_zero_area(pack->bitmap, bpf_prog_chunk_count(), 0,
nbits, 0);
- if (pos < BPF_PROG_CHUNK_COUNT)
+ if (pos < bpf_prog_chunk_count())
goto found_free_area;
}
@@ -904,12 +924,12 @@ static void bpf_prog_pack_free(struct bpf_binary_header *hdr)
unsigned long pos;
void *pack_ptr;
- if (hdr->size > BPF_PROG_MAX_PACK_PROG_SIZE) {
+ if (hdr->size > bpf_prog_pack_size) {
module_memfree(hdr);
return;
}
- pack_ptr = (void *)((unsigned long)hdr & ~(BPF_PROG_PACK_SIZE - 1));
+ pack_ptr = (void *)((unsigned long)hdr & ~(bpf_prog_pack_size - 1));
mutex_lock(&pack_mutex);
list_for_each_entry(tmp, &pack_list, list) {
@@ -926,8 +946,8 @@ static void bpf_prog_pack_free(struct bpf_binary_header *hdr)
pos = ((unsigned long)hdr - (unsigned long)pack_ptr) >> BPF_PROG_CHUNK_SHIFT;
bitmap_clear(pack->bitmap, pos, nbits);
- if (bitmap_find_next_zero_area(pack->bitmap, BPF_PROG_CHUNK_COUNT, 0,
- BPF_PROG_CHUNK_COUNT, 0) == 0) {
+ if (bitmap_find_next_zero_area(pack->bitmap, bpf_prog_chunk_count(), 0,
+ bpf_prog_chunk_count(), 0) == 0) {
list_del(&pack->list);
module_memfree(pack->ptr);
kfree(pack);
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