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Date:   Fri, 18 Jun 2021 12:47:13 -0700 (PDT)
From:   David Rientjes <rientjes@google.com>
To:     Claudio Imbrenda <imbrenda@linux.ibm.com>
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, Uladzislau Rezki <urezki@gmail.com>,
        Nicholas Piggin <npiggin@gmail.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>,
        Christoph Hellwig <hch@infradead.org>
Subject: Re: [PATCH v4 1/2] mm/vmalloc: add vmalloc_no_huge
In-Reply-To: <20210614132357.10202-2-imbrenda@linux.ibm.com>
Message-ID: <1ab3bba4-dc91-4f8-ecd5-b18b17ec6d8@google.com>
References: <20210614132357.10202-1-imbrenda@linux.ibm.com> <20210614132357.10202-2-imbrenda@linux.ibm.com>
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On Mon, 14 Jun 2021, Claudio Imbrenda wrote:

> Commit 121e6f3258fe3 ("mm/vmalloc: hugepage vmalloc mappings") added
> support for hugepage vmalloc mappings, it also added the flag
> VM_NO_HUGE_VMAP for __vmalloc_node_range to request the allocation to
> be performed with 0-order non-huge 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 non-huge pages, because of a hardware limitation.
> 
> This patch adds the function vmalloc_no_huge, which works like vmalloc,
> but it is guaranteed to always back the mapping using small pages. This
> new function is exported, therefore it is usable by modules.
> 
> Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
> Reviewed-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
> Acked-by: Nicholas Piggin <npiggin@gmail.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Nicholas Piggin <npiggin@gmail.com>
> Cc: Uladzislau Rezki (Sony) <urezki@gmail.com>
> Cc: Catalin Marinas <catalin.marinas@arm.com>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: David Rientjes <rientjes@google.com>
> Cc: Christoph Hellwig <hch@infradead.org>

Acked-by: David Rientjes <rientjes@google.com>