linux-kernel - Re: [Cocci] [PATCH] coccinelle: api: add kvfree script

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Message-ID: <alpine.DEB.2.21.2006052318310.28300@hadrien>
Date:   Fri, 5 Jun 2020 23:19:32 +0200 (CEST)
From:   Julia Lawall <julia.lawall@...ia.fr>
To:     Denis Efremov <efremov@...ux.com>
cc:     cocci@...teme.lip6.fr, linux-kernel@...r.kernel.org
Subject: Re: [Cocci] [PATCH] coccinelle: api: add kvfree script



On Sat, 6 Jun 2020, Denis Efremov wrote:

> On 6/5/20 11:51 PM, Julia Lawall wrote:
> > Is there a strong reason for putting the choice rule first?  It may make
> > things somewhat slower than necessary, if it matches in many places,
> > because the opportunity rule will have to detect that it doesn't care
> > about all of those places.
>
> No, I didn't know that order of rules matters. I just checked it, my PC
> shows no difference in exec time if I swap these rules.

OK, probably choice doesn't match in very many places, so there is not
much impact.

julia

>
> "choice" doesn't check the size. "opportunity" is more strict.
> The motivation for adding 2 rules is that we could recommend to use
> kvmalloc* only when there is a size condition. At the same time, we
> should skip all if (...) {kmalloc()} else {vmalloc()},
> res = kmalloc() if (!res) {vmalloc()} cases as false positives.
>
> It seems that it's not possible to use subexpression rule
> "expression size <= choice.E" in this case.
>
> > Also, there is no need to exceed 80 characters here.  You can put a
> > newline in the middle of a \( ... \)
>
> Ok, I will fix it in v2 after all comments/suggestions.
>
> Thanks,
> Denis
>