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Date:   Wed, 19 Jan 2022 13:48:13 +0000
From:   Matthew Wilcox <willy@...radead.org>
To:     Kefeng Wang <wangkefeng.wang@...wei.com>
Cc:     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,
        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>
Subject: Re: [PATCH v2 1/3] mm: vmalloc: Let user to control huge vmalloc
 default behavior

On Wed, Jan 19, 2022 at 09:44:20PM +0800, Kefeng Wang wrote:
> 
> On 2022/1/19 21:22, Matthew Wilcox wrote:
> > On Wed, Jan 19, 2022 at 08:57:58PM +0800, Kefeng Wang wrote:
> > > 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,
> > But why do only some products want it?  What goes wrong if all products
> > enable it?  Features should be auto-tuning, not relying on admins to
> > understand them.
> 
> Because this feature will use more memory for vmalloc/vmap, that's why we
> add some explicit
> interfaces as said above in our kernel to control the user.

Have you validated that?  What sort of performance penalty do you see?

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