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Date:   Wed, 9 Jun 2021 18:28:09 +0200
From:   Claudio Imbrenda <imbrenda@linux.ibm.com>
To:     Christoph Hellwig <hch@infradead.org>
Cc:     linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
        linux-s390@vger.kernel.org, frankja@linux.ibm.com,
        borntraeger@de.ibm.com, cohuck@redhat.com, david@redhat.com,
        linux-mm@kvack.org, Andrew Morton <akpm@linux-foundation.org>,
        Nicholas Piggin <npiggin@gmail.com>,
        Uladzislau Rezki <urezki@gmail.com>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>,
        David Rientjes <rientjes@google.com>
Subject: Re: [PATCH v2 1/2] mm/vmalloc: export __vmalloc_node_range
Message-ID: <20210609182809.7ae07aad@ibm-vm>
In-Reply-To: <YMDlVdB8m62AhbB7@infradead.org>
References: <20210608180618.477766-1-imbrenda@linux.ibm.com>
        <20210608180618.477766-2-imbrenda@linux.ibm.com>
        <YMDlVdB8m62AhbB7@infradead.org>
Organization: IBM
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On Wed, 9 Jun 2021 16:59:17 +0100
Christoph Hellwig <hch@infradead.org> wrote:

> On Tue, Jun 08, 2021 at 08:06:17PM +0200, Claudio Imbrenda wrote:
> > The recent patches to add support for hugepage vmalloc mappings
> > added a flag for __vmalloc_node_range to allow to request small
> > pages. This flag is not accessible when calling vmalloc, the only
> > option is to call directly __vmalloc_node_range, which is not
> > exported.
> > 
> > This means that a module can't vmalloc memory with small pages.
> > 
> > Case in point: KVM on s390x needs to vmalloc a large area, and it
> > needs to be mapped with small pages, because of a hardware
> > limitation.
> > 
> > This patch exports __vmalloc_node_range so it can be used in modules
> > too.  
> 
> No.  I spent a lot of effort to mak sure such a low-level API is
> not exported.

ok, but then how can we vmalloc memory with small pages from KVM?