From: Song Liu <email@example.com>
To: Claudio Imbrenda <firstname.lastname@example.org>
Cc: Christoph Hellwig <email@example.com>,
Nicholas Piggin <firstname.lastname@example.org>,
Song Liu <email@example.com>,
Linux Memory Management List <firstname.lastname@example.org>,
bpf <email@example.com>, Networking <firstname.lastname@example.org>,
X86 ML <email@example.com>, Alexei Starovoitov <firstname.lastname@example.org>,
Daniel Borkmann <email@example.com>,
Kernel Team <Kernelfirstname.lastname@example.org>,
Subject: Re: [PATCH bpf 0/4] introduce HAVE_ARCH_HUGE_VMALLOC_FLAG for bpf_prog_pack
Date: Fri, 8 Apr 2022 21:22:47 +0000 [thread overview]
Message-ID: <3D4CC64A-1852-45B3-BA35-17EAD2504447@fb.com> (raw)
> On Apr 8, 2022, at 3:08 AM, Claudio Imbrenda <email@example.com> wrote:
> On Thu, 7 Apr 2022 19:57:25 +0000
> Song Liu <firstname.lastname@example.org> wrote:
>> Hi Nicholas and Claudio,
>>> On Apr 5, 2022, at 4:54 PM, Song Liu <email@example.com> wrote:
>>>> On Apr 5, 2022, at 12:07 AM, Christoph Hellwig <firstname.lastname@example.org> wrote:
>>>> On Fri, Apr 01, 2022 at 10:22:00PM +0000, Song Liu wrote:
>>>>>>> Please fix the underlying issues instead of papering over them and
>>>>>>> creating a huge maintainance burden for others.
>>>>> After reading the code a little more, I wonder what would be best strategy.
>>>>> IIUC, most of the kernel is not ready for huge page backed vmalloc memory.
>>>>> For example, all the module_alloc cannot work with huge pages at the moment.
>>>>> And the error Paul Menzel reported in drm_fb_helper.c will probably hit
>>>>> powerpc with 5.17 kernel as-is? (trace attached below)
>>>>> Right now, we have VM_NO_HUGE_VMAP to let a user to opt out of huge pages.
>>>>> However, given there are so many users of vmalloc, vzalloc, etc., we
>>>>> probably do need a flag for the user to opt-in?
>>>>> Does this make sense? Any recommendations are really appreciated.
>>>> I think there is multiple aspects here:
>>>> - if we think that the kernel is not ready for hugepage backed vmalloc
>>>> in general we need to disable it in powerpc for now.
>>> Nicholas and Claudio,
>>> What do you think about the status of hugepage backed vmalloc on powerpc?
>>> I found module_alloc and kvm_s390_pv_alloc_vm() opt-out of huge pages.
>>> But I am not aware of users that benefit from huge pages (except vfs hash,
>>> which was mentioned in 8abddd968a30). Does an opt-in flag (instead of
>>> current opt-out flag, VM_NO_HUGE_VMAP) make sense to you?
>> Could you please share your comments on this? Specifically, does it make
>> sense to replace VM_NO_HUGE_VMAP with an opt-in flag? If we think current
>> opt-out flag is better approach, what would be the best practice to find
>> all the cases to opt-out?
> An opt in flag would surely make sense, and it would be more backwards
> compatible with existing code. That way each user can decide whether to
> fix the code to allow for hugepages, if possible at all. For example,
> the case you mentioned for s390 (kvm_s390_pv_alloc_vm) would not be
> fixable, because of a hardware limitation (the whole area _must_ be
> mapped with 4k pages)
> If the consensus were to keep the current opt-put, then I guess each
> user would have to check each usage of vmalloc and similar, and see if
> anything breaks. To be honest, I think an opt-out would only be
> possible after having the opt-in for a (long) while, when most users
> would have fixed their code.
> In short, I fully support opt-in.
I will prepare patches to replace VM_NO_HUGE_VMAP with an opt-in flag,
and use the new flag in BPF. Please let me know any comments/suggestions
ont this direction.
prev parent reply other threads:[~2022-04-08 21:24 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-03-30 22:56 [PATCH bpf 0/4] introduce HAVE_ARCH_HUGE_VMALLOC_FLAG for bpf_prog_pack Song Liu
2022-03-30 22:56 ` [PATCH bpf 1/4] x86: disable HAVE_ARCH_HUGE_VMALLOC Song Liu
2022-03-30 23:47 ` Thomas Gleixner
2022-03-30 22:56 ` [PATCH bpf 2/4] vmalloc: introduce HAVE_ARCH_HUGE_VMALLOC_FLAG Song Liu
2022-03-30 23:40 ` Edgecombe, Rick P
2022-03-31 0:26 ` Song Liu
2022-03-30 22:56 ` [PATCH bpf 3/4] x86: select HAVE_ARCH_HUGE_VMALLOC_FLAG for X86_64 Song Liu
2022-03-30 23:54 ` Thomas Gleixner
2022-03-31 0:30 ` Song Liu
2022-03-30 22:56 ` [PATCH bpf 4/4] bpf: use __vmalloc_node_range() with VM_TRY_HUGE_VMAP for bpf_prog_pack Song Liu
2022-03-31 0:00 ` Thomas Gleixner
2022-03-31 0:31 ` Song Liu
2022-03-31 0:04 ` [PATCH bpf 0/4] introduce HAVE_ARCH_HUGE_VMALLOC_FLAG " Edgecombe, Rick P
2022-03-31 0:46 ` Song Liu
2022-03-31 16:19 ` Edgecombe, Rick P
2022-03-31 5:37 ` Christoph Hellwig
2022-03-31 23:59 ` Song Liu
2022-04-01 22:22 ` Song Liu
2022-04-05 7:07 ` Christoph Hellwig
2022-04-05 23:54 ` Song Liu
2022-04-07 19:57 ` Song Liu
2022-04-08 10:08 ` Claudio Imbrenda
2022-04-08 21:22 ` Song Liu [this message]
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