linux-kernel - Re: [PATCH RFC 3/4] mm, slab: add static key for should

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Date: Sat, 1 Jun 2024 22:57:29 +0200
From: Vlastimil Babka <vbabka@...e.cz>
To: Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc: Akinobu Mita <akinobu.mita@...il.com>, Christoph Lameter <cl@...ux.com>,
 David Rientjes <rientjes@...gle.com>, Alexei Starovoitov <ast@...nel.org>,
 Daniel Borkmann <daniel@...earbox.net>, Andrii Nakryiko <andrii@...nel.org>,
 "Naveen N. Rao" <naveen.n.rao@...ux.ibm.com>,
 Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>,
 "David S. Miller" <davem@...emloft.net>,
 Masami Hiramatsu <mhiramat@...nel.org>, Steven Rostedt
 <rostedt@...dmis.org>, Mark Rutland <mark.rutland@....com>,
 Jiri Olsa <jolsa@...nel.org>, Roman Gushchin <roman.gushchin@...ux.dev>,
 Hyeonggon Yoo <42.hyeyoo@...il.com>, LKML <linux-kernel@...r.kernel.org>,
 linux-mm <linux-mm@...ck.org>, bpf <bpf@...r.kernel.org>,
 linux-trace-kernel <linux-trace-kernel@...r.kernel.org>
Subject: Re: [PATCH RFC 3/4] mm, slab: add static key for should_failslab()

On 5/31/24 6:43 PM, Alexei Starovoitov wrote:
> On Fri, May 31, 2024 at 2:33 AM Vlastimil Babka <vbabka@...e.cz> wrote:
>>         might_alloc(flags);
>>
>> -       if (unlikely(should_failslab(s, flags)))
>> -               return NULL;
>> +       if (static_branch_unlikely(&should_failslab_active)) {
>> +               if (should_failslab(s, flags))
>> +                       return NULL;
>> +       }
> 
> makes sense.
> Acked-by: Alexei Starovoitov <ast@...nel.org>

Thanks :) but please note the cover letter where I explain how I need help
with the bpftrace side (and ftrace, but that seems sorted). Without that
part, bpftrace will silently stop doing the injection as the static key will
remain disabled.

> Do you have any microbenchmark numbers before/after this optimization?

Also in cover letter, but will include it in the patch commit log next time.