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From:   Marco Elver <elver@google.com>
Date:   Fri, 2 Oct 2020 23:28:12 +0200
Message-ID: <CANpmjNN7s3o4DYbP64iLYo0MeDWciQnKd61njJKLsiZv+ZLQdA@mail.gmail.com>
Subject: Re: [PATCH v4 01/11] mm: add Kernel Electric-Fence infrastructure
To:     Jann Horn <jannh@google.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
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On Fri, 2 Oct 2020 at 21:32, Jann Horn <jannh@google.com> wrote:

> > That's another check; we don't want to make this more expensive.
>
> Ah, right, I missed that this is the one piece of KFENCE that is
> actually really hot code until Dmitry pointed that out.
>
> But actually, can't you reduce how hot this is for SLUB by moving
> is_kfence_address() down into the freeing slowpath? At the moment you
> use it in slab_free_freelist_hook(), which is in the super-hot
> fastpath, but you should be able to at least move it down into
> __slab_free()...
>
> Actually, you already have hooked into __slab_free(), so can't you
> just get rid of the check in the slab_free_freelist_hook()?

I missed this bit: the loop that follows wants the free pointer, so I
currently see how this might work. :-/

We'll look at your other email re optimizing is_kfence_address() next
week; and thank you for the detailed comments thus far!

Thanks,
-- Marco