From: Andrey Ryabinin <aryabinin@virtuozzo.com>
To: Andrey Konovalov <andreyknvl@google.com>
Cc: Christoph Lameter <cl@linux.com>,
Pekka Enberg <penberg@kernel.org>,
David Rientjes <rientjes@google.com>,
Joonsoo Kim <iamjoonsoo.kim@lge.com>,
Andrew Morton <akpm@linux-foundation.org>,
Alexander Potapenko <glider@google.com>,
Dmitry Vyukov <dvyukov@google.com>,
Linux Memory Management List <linux-mm@kvack.org>,
LKML <linux-kernel@vger.kernel.org>,
kasan-dev <kasan-dev@googlegroups.com>,
Kostya Serebryany <kcc@google.com>
Subject: Re: [PATCH] kasan, slub: fix handling of kasan_slab_free hook
Date: Wed, 7 Mar 2018 15:43:51 +0300 [thread overview]
Message-ID: <c7249bc3-8488-00c9-666a-8d31fb3feb83@virtuozzo.com> (raw)
In-Reply-To: <CAAeHK+y4hze8CUDMJ_G6W+diBO88+WYu892SK9QAt36y8nbZYQ@mail.gmail.com>
On 03/06/2018 08:42 PM, Andrey Konovalov wrote:
>>> - if (s->flags & SLAB_KASAN && !(s->flags & SLAB_TYPESAFE_BY_RCU))
>>> - return;
>>> - do_slab_free(s, page, head, tail, cnt, addr);
>>> + slab_free_freelist_hook(s, &head, &tail);
>>> + if (head != NULL)
>>
>> That's an additional branch in non-debug fast-path. Find a way to avoid this.
>
> Hm, there supposed to be a branch here. We either have objects that we
> need to free, or we don't, and we need to do different things in those
> cases. Previously this was done with a hardcoded "if (s->flags &
> SLAB_KASAN && ..." statement, not it's a different "if (head !=
> NULL)".
>
They are different. "if (s->flags & SLAB_KASAN && ..." can be optimized away by compiler when CONFIG_KASAN=n,
"if (head != NULL)" - can not.
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prev parent reply other threads:[~2018-03-07 12:44 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-02-23 15:53 Andrey Konovalov
2018-03-02 12:10 ` Andrey Ryabinin
2018-03-06 17:42 ` Andrey Konovalov
2018-03-06 17:47 ` Andrey Konovalov
2018-03-07 12:43 ` Andrey Ryabinin [this message]
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