linux-kernel - Re: [PATCH v2] mm: kmalloc_index: make compiler break when size is not supported

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Message-ID: <20210511030343.GB98904@hyeyoo>
Date:   Tue, 11 May 2021 12:03:43 +0900
From:   Hyeonggon Yoo <42.hyeyoo@...il.com>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Vlastimil Babka <vbabka@...e.cz>, cl@...ux.com, penberg@...nel.org,
        rientjes@...gle.com, iamjoonsoo.kim@....com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] mm: kmalloc_index: make compiler break when size is
 not supported

On Mon, May 10, 2021 at 04:44:09PM +0100, Matthew Wilcox wrote:
> On Tue, May 11, 2021 at 12:02:30AM +0900, Hyeonggon Yoo wrote:
> > @@ -382,8 +385,8 @@ static __always_inline unsigned int kmalloc_index(size_t size)
> >  	if (size <=  8 * 1024 * 1024) return 23;
> >  	if (size <=  16 * 1024 * 1024) return 24;
> >  	if (size <=  32 * 1024 * 1024) return 25;
> > -	if (size <=  64 * 1024 * 1024) return 26;
> > -	BUG();
> > +
> > +	BUILD_BUG_ON_MSG(1, "unexpected size in kmalloc_index()");
> 
> we're being encouraged to use static_assert() these days.
> https://en.cppreference.com/w/c/language/_Static_assert
> 

can you tell me difference between static_assert and BUILD_BUG_ON?
it seems that mm subsystem does not make use of it now.