linux-kernel - Re: [PATCH] bpf: Convert lpm_trie::lock to 'raw_spinlock

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Message-ID: <CAADnVQJBGKioLA0JuyCQdD-jRKn2bpb7A7r6Yo4drBb9G1tvbg@mail.gmail.com>
Date: Sat, 16 Nov 2024 08:42:49 -0800
From: Alexei Starovoitov <alexei.starovoitov@...il.com>
To: Thomas Weißschuh <linux@...ssschuh.net>
Cc: Sebastian Andrzej Siewior <bigeasy@...utronix.de>, Thomas Gleixner <tglx@...utronix.de>, 
	Kunwu Chan <kunwu.chan@...ux.dev>, Alexei Starovoitov <ast@...nel.org>, 
	Daniel Borkmann <daniel@...earbox.net>, Andrii Nakryiko <andrii@...nel.org>, 
	Martin KaFai Lau <martin.lau@...ux.dev>, Eddy Z <eddyz87@...il.com>, Song Liu <song@...nel.org>, 
	Yonghong Song <yonghong.song@...ux.dev>, John Fastabend <john.fastabend@...il.com>, 
	KP Singh <kpsingh@...nel.org>, Stanislav Fomichev <sdf@...ichev.me>, Hao Luo <haoluo@...gle.com>, 
	Jiri Olsa <jolsa@...nel.org>, clrkwllms@...nel.org, 
	Steven Rostedt <rostedt@...dmis.org>, bpf <bpf@...r.kernel.org>, 
	LKML <linux-kernel@...r.kernel.org>, linux-rt-devel@...ts.linux.dev, 
	syzbot+b506de56cbbb63148c33@...kaller.appspotmail.com, 
	Thomas Weißschuh <thomas.weissschuh@...utronix.de>
Subject: Re: [PATCH] bpf: Convert lpm_trie::lock to 'raw_spinlock_t'

On Sat, Nov 16, 2024 at 8:15 AM Thomas Weißschuh <linux@...ssschuh.net> wrote:
>
> On 2024-11-16 08:01:49-0800, Alexei Starovoitov wrote:
> > On Sat, Nov 16, 2024 at 1:21 AM Sebastian Andrzej Siewior
> > <bigeasy@...utronix.de> wrote:
> > >
> > > On 2024-11-15 23:29:31 [+0100], Thomas Gleixner wrote:
> > > > IIRC, BPF has it's own allocator which can be used everywhere.
> > >
> > > Thomas Weißschuh made something. It appears to work. Need to take a
> > > closer look.
> >
> > Any more details?
> > bpf_mem_alloc is a stop gap.
>
> It is indeed using bpf_mem_alloc.
> It is a fairly straightforward conversion, using one cache for
> intermediate and one for non-intermediate nodes.

Sounds like you're proposing to allocate two lpm specific bpf_ma-s ?
Just use bpf_global_ma.
More ma-s means more memory pinned in bpf specific freelists.
That's the main reason to teach slub and page_alloc about bpf requirements.
All memory should be shared by all subsystems.
Custom memory pools / freelists, whether it's bpf, networking
or whatever else, is a pain point for somebody.
The kernel needs to be optimal for all use cases.

> I'll try to send it early next week.

Looking forward.

> > As Vlastimil Babka suggested long ago:
> > https://lwn.net/Articles/974138/
> > "...next on the target list is the special allocator used by the BPF
> > subsystem. This allocator is intended to succeed in any calling
> > context, including in non-maskable interrupts (NMIs). BPF maintainer
> > Alexei Starovoitov is evidently in favor of this removal if SLUB is
> > able to handle the same use cases..."
> >
> > Here is the first step:
> > https://lore.kernel.org/bpf/20241116014854.55141-1-alexei.starovoitov@gmail.com/