netdev - Re: [PATCH bpf 1/2] vmalloc: replace VM_NO_HUGE_VMAP with VM_ALLOW_HUGE

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Message-ID: <4D0216A9-E667-4936-8FF7-A1B94E973720@fb.com>
Date:   Sun, 10 Apr 2022 01:25:40 +0000
From:   Song Liu <songliubraving@...com>
To:     Christoph Hellwig <hch@...radead.org>
CC:     Song Liu <song@...nel.org>, bpf <bpf@...r.kernel.org>,
        Networking <netdev@...r.kernel.org>,
        Linux Memory Management List <linux-mm@...ck.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Kernel Team <Kernel-team@...com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "rick.p.edgecombe@...el.com" <rick.p.edgecombe@...el.com>,
        "imbrenda@...ux.ibm.com" <imbrenda@...ux.ibm.com>
Subject: Re: [PATCH bpf 1/2] vmalloc: replace VM_NO_HUGE_VMAP with
 VM_ALLOW_HUGE_VMAP



> On Apr 8, 2022, at 10:28 PM, Christoph Hellwig <hch@...radead.org> wrote:
> 
> On Fri, Apr 08, 2022 at 03:34:42PM -0700, Song Liu wrote:
>> Huge page backed vmalloc memory could benefit performance in many cases.
>> Since some users of vmalloc may not be ready to handle huge pages,
>> VM_NO_HUGE_VMAP was introduced to allow vmalloc users to opt-out huge
>> pages. However, it is not easy to add VM_NO_HUGE_VMAP to all the users
>> that may try to allocate >= PMD_SIZE pages, but are not ready to handle
>> huge pages properly.
>> 
>> Replace VM_NO_HUGE_VMAP with an opt-in flag, VM_ALLOW_HUGE_VMAP, so that
>> users that benefit from huge pages could ask specificially.
> 
> Given that the huge page backing was added explicitly for some big boot
> time allocated hashed,those should probably have the VM_ALLOW_HUGE_VMAP
> added from the start (maybe not in this patch, but certainly in this
> series).  We'll probably also need a vmalloc_huge interface for those.

Will add it in v2. 

Thanks,
Song