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

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Date:   Wed, 19 Jan 2022 20:57:58 +0800
From:   Kefeng Wang <wangkefeng.wang@...wei.com>
To:     Nicholas Piggin <npiggin@...il.com>,
        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>,
        <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


On 2022/1/18 10:52, Nicholas Piggin wrote:
> 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.

nohugevmalloc is like blacklists, on the other hand, Add a 
HUGE_VMALLOC_DEFAULT_ENABLED

to close hugevmalloc default and enable it only via hugevmalloc=on is 
whiteList.


Only parts of our products wants this feature,  we add some interfaces 
which only

alloc hugevmalloc for them, eg, 
vmap_hugepage/vmalloc_hugepage/remap_vmalloc_hugepage_range..

for our products, but it's not the choice of most products, also add 
nohugevmalloc

for most products is expensive, so this is the reason for adding the patch.

more config/cmdline are more flexible for test/products，

>
> 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.

but yes, this patch is optional， could others give some more comments 
about this way？

Thanks.

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