linux-kernel - Re: [PATCH v5 5/8] mm: HUGE

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Message-ID: <2bd2e0a4-37bc-680d-1e11-f6f44204c317@csgroup.eu>
Date:   Fri, 21 Aug 2020 14:43:58 +0200
From:   Christophe Leroy <christophe.leroy@...roup.eu>
To:     Nicholas Piggin <npiggin@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org
Cc:     Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        linux-arch@...r.kernel.org, linux-kernel@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, Zefan Li <lizefan@...wei.com>
Subject: Re: [PATCH v5 5/8] mm: HUGE_VMAP arch support cleanup



Le 21/08/2020 à 12:39, Nicholas Piggin a écrit :
> Excerpts from Christophe Leroy's message of August 21, 2020 3:40 pm:
>>
>>
>> Le 21/08/2020 à 06:44, Nicholas Piggin a écrit :
>>> This changes the awkward approach where architectures provide init
>>> functions to determine which levels they can provide large mappings for,
>>> to one where the arch is queried for each call.
>>>
>>> This removes code and indirection, and allows constant-folding of dead
>>> code for unsupported levels.
>>
>> I think that in order to allow constant-folding of dead code for
>> unsupported levels, you must define arch_vmap_xxx_supported() as static
>> inline in a .h
>>
>> If you have them in .c files, you'll get calls to tiny functions that
>> will always return false, but will still be called and dead code won't
>> be eliminated. And performance wise, that's probably not optimal either.
> 
> Yeah that's true actually, I think I didn't find a good place to add
> the prototypes in the arch code but I'll have another look and either
> rewrite the changelog or remove it. Although this does get a step closer
> at least.
> 

linux/vmalloc.h includes asm/vmalloc.h
Should it go there ?

Christophe