linux-kernel - Re: [PATCH v2 1/3] mm: vmalloc: Let user to control huge vmalloc default behavior

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Date:   Tue, 18 Jan 2022 12:52:56 +1000
From:   Nicholas Piggin <npiggin@...il.com>
To:     Andrew Morton <akpm@...ux-foundation.org>,
        Jonathan Corbet <corbet@....net>,
        linux-arm-kernel@...ts.infradead.org, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linuxppc-dev@...ts.ozlabs.org,
        Kefeng Wang <wangkefeng.wang@...wei.com>, x86@...nel.org
Cc:     Benjamin
 Herrenschmidt 
        <benh@...nel.crashing.org>, Borislav Petkov <bp@...en8.de>,
        Catalin Marinas <catalin.marinas@....com>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Paul Mackerras <paulus@...ba.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Will Deacon <will@...nel.org>,
        Matthew Wilcox <willy@...radead.org>
Subject: Re: [PATCH v2 1/3] mm: vmalloc: Let user to control huge vmalloc
 default behavior

Excerpts from Kefeng Wang's message of December 28, 2021 12:59 am:
> Introduce HUGE_VMALLOC_DEFAULT_ENABLED and make it default y, this
> let user to choose whether or not enable huge vmalloc mappings by
> default.
> 
> Meanwhile, add new hugevmalloc=on/off parameter to enable or disable
> this feature at boot time, nohugevmalloc is still supported and
> equivalent to hugevmalloc=off.

Runtime options are bad enough, Kconfig and boot options are even worse.

The 'nohugevmalloc' option mirrors 'nohugeiomap' and is not expected to
ever be understood by an administrator unless a kernel developer is 
working with them to hunt down a regression.

IMO there should be no new options. You could switch it off for 
CONFIG_BASE_SMALL perhaps, and otherwise just try to work on heuristics
first. Bring in new options once it's proven they're needed.

Aside from that, thanks for working on these ports, great work.

Thanks,
Nick