Re: [PATCH v14 01/13] sk_run_filter: add BPF_S_ANC_SECCOMP_LD_W

[Eric Dumazet]

On Tue, 2012-03-13 at 11:04 +0100, Indan Zupancic wrote:
> Hello,
> 
> I made a quick pseudo-patch for BPF JIT support. As far as I can tell,
> the actual code itself is very simple, just:
> 

> -	bpf_jit_compile(fp);
> +	jit = bpf_jit_compile(fp->insns, fp->len, 1);
> +	if (jit) {
> +		fp->bpf_func = jit;
> +		/* Free unused insns memory */
> +		newfp = krealloc(fp, sizeof(*fp), GFP_KERNEL);
> +		if (newfp)
> +			fp = newfp;
> +	}
> 
>  	old_fp = rcu_dereference_protected(sk->sk_filter,
>  					   sock_owned_by_user(sk));

Dont mix unrelated changes in a single patch.

Current krealloc() doesnt alloc a new area if the current one is bigger
than 'new_size', but this might change in next kernel versions.

So this part of your patch does nothing.

If it did, this kind of 'optimization' can actually be not good, because
sizeof(*fp) is small enough (less than half cache line size) to trigger
a possible false sharing issue. (other part of the cache line could be
used to hold a often dirtied object)



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