Re: [PATCH v4 bpf-next 5/8] bpf: use module_alloc_huge for bpf_prog_pack

From: Mike Rapoport <rppt@kernel.org>
To: Song Liu <song@kernel.org>
Cc: linux-kernel@vger.kernel.org, bpf@vger.kernel.org,
	linux-mm@kvack.org, ast@kernel.org, daniel@iogearbox.net,
	peterz@infradead.org, mcgrof@kernel.org,
	torvalds@linux-foundation.org, rick.p.edgecombe@intel.com,
	kernel-team@fb.com
Subject: Re: [PATCH v4 bpf-next 5/8] bpf: use module_alloc_huge for bpf_prog_pack
Date: Tue, 24 May 2022 10:22:00 +0300	[thread overview]
Message-ID: <YoyHmGoEN7kQSw3N@kernel.org> (raw)
In-Reply-To: <20220520235758.1858153-6-song@kernel.org>

On Fri, May 20, 2022 at 04:57:55PM -0700, Song Liu wrote:
> Use module_alloc_huge for bpf_prog_pack so that BPF programs sit on
> PMD_SIZE pages. This benefits system performance by reducing iTLB miss
> rate. Benchmark of a real web service workload shows this change gives
> another ~0.2% performance boost on top of PAGE_SIZE bpf_prog_pack
> (which improve system throughput by ~0.5%).
> 
> Also, remove set_vm_flush_reset_perms() from alloc_new_pack() and use
> set_memory_[nx|rw] in bpf_prog_pack_free(). This is because
> VM_FLUSH_RESET_PERMS does not work with huge pages yet. [1]
> 
> [1] https://lore.kernel.org/bpf/aeeeaf0b7ec63fdba55d4834d2f524d8bf05b71b.camel@intel.com/
> Suggested-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
> Signed-off-by: Song Liu <song@kernel.org>
> ---
>  kernel/bpf/core.c | 12 +++++++-----
>  1 file changed, 7 insertions(+), 5 deletions(-)
> 
> diff --git a/kernel/bpf/core.c b/kernel/bpf/core.c
> index cacd8684c3c4..b64d91fcb0ba 100644
> --- a/kernel/bpf/core.c
> +++ b/kernel/bpf/core.c
> @@ -857,7 +857,7 @@ static size_t select_bpf_prog_pack_size(void)
>  	void *ptr;
>  
>  	size = BPF_HPAGE_SIZE * num_online_nodes();
> -	ptr = module_alloc(size);
> +	ptr = module_alloc_huge(size);
>  
>  	/* Test whether we can get huge pages. If not just use PAGE_SIZE
>  	 * packs.
> @@ -881,7 +881,7 @@ static struct bpf_prog_pack *alloc_new_pack(bpf_jit_fill_hole_t bpf_fill_ill_ins
>  		       GFP_KERNEL);
>  	if (!pack)
>  		return NULL;
> -	pack->ptr = module_alloc(bpf_prog_pack_size);
> +	pack->ptr = module_alloc_huge(bpf_prog_pack_size);
>  	if (!pack->ptr) {
>  		kfree(pack);
>  		return NULL;
> @@ -890,7 +890,6 @@ static struct bpf_prog_pack *alloc_new_pack(bpf_jit_fill_hole_t bpf_fill_ill_ins
>  	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);
>  	return pack;
> @@ -909,10 +908,9 @@ static void *bpf_prog_pack_alloc(u32 size, bpf_jit_fill_hole_t bpf_fill_ill_insn
>  
>  	if (size > bpf_prog_pack_size) {
>  		size = round_up(size, PAGE_SIZE);
> -		ptr = module_alloc(size);
> +		ptr = module_alloc_huge(size);
>  		if (ptr) {
>  			bpf_fill_ill_insns(ptr, size);
> -			set_vm_flush_reset_perms(ptr);
>  			set_memory_ro((unsigned long)ptr, size / PAGE_SIZE);
>  			set_memory_x((unsigned long)ptr, size / PAGE_SIZE);
>  		}
> @@ -949,6 +947,8 @@ static void bpf_prog_pack_free(struct bpf_binary_header *hdr)
>  
>  	mutex_lock(&pack_mutex);
>  	if (hdr->size > bpf_prog_pack_size) {
> +		set_memory_nx((unsigned long)hdr, hdr->size / PAGE_SIZE);
> +		set_memory_rw((unsigned long)hdr, hdr->size / PAGE_SIZE);

set_memory_{nx,rw} can fail. Please take care of error handling.

>  		module_memfree(hdr);
>  		goto out;
>  	}
> @@ -975,6 +975,8 @@ static void bpf_prog_pack_free(struct bpf_binary_header *hdr)
>  	if (bitmap_find_next_zero_area(pack->bitmap, bpf_prog_chunk_count(), 0,
>  				       bpf_prog_chunk_count(), 0) == 0) {
>  		list_del(&pack->list);
> +		set_memory_nx((unsigned long)pack->ptr, bpf_prog_pack_size / PAGE_SIZE);
> +		set_memory_rw((unsigned long)pack->ptr, bpf_prog_pack_size / PAGE_SIZE);

ditto.

>  		module_memfree(pack->ptr);
>  		kfree(pack);
>  	}
> -- 
> 2.30.2
> 
> 

-- 
Sincerely yours,
Mike.