From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-15.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id B064BC56202 for ; Thu, 26 Nov 2020 09:56:41 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 37682208CA for ; Thu, 26 Nov 2020 09:56:40 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="SDO+oy5Y" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2387470AbgKZJ4Z (ORCPT ); Thu, 26 Nov 2020 04:56:25 -0500 Received: from us-smtp-delivery-124.mimecast.com ([63.128.21.124]:43928 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726099AbgKZJ4Y (ORCPT ); Thu, 26 Nov 2020 04:56:24 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1606384582; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=XL2h/hir+tmct6ROumYIQmrzt7JrIUdXPqptvlCNWjc=; b=SDO+oy5YgaCWMa5ozRHVXyan/7v4X/DnKd6P5hkhvJCBvEfiABJtlwtOi4/505zEj6oYw5 VVjbvZZGElHY+Rt1KKiVrS9y8aZGCXgPY6Cf9Wgh060Qg8xlInW1DjuQHEQOpQjydemzji XnW2tFolfUp63FsKr86vwLYpYfs91n4= Received: from mail-ed1-f71.google.com (mail-ed1-f71.google.com [209.85.208.71]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-74-Ozlmav_SOGm6ACRil7JVzQ-1; Thu, 26 Nov 2020 04:56:16 -0500 X-MC-Unique: Ozlmav_SOGm6ACRil7JVzQ-1 Received: by mail-ed1-f71.google.com with SMTP id s7so809571eds.17 for ; Thu, 26 Nov 2020 01:56:14 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:in-reply-to:references:date :message-id:mime-version; bh=XL2h/hir+tmct6ROumYIQmrzt7JrIUdXPqptvlCNWjc=; b=N3V8QBOPgzvrdLZAEkmcjM10a29YOyY6jXS5tPAp2dtqufFoloreeErFN8vfNhC8AY 6tivcMPzWmI4jQumRYFOA2uKGWHxhNv8hHTv0tNiUcUCaRBeRGCRU+uLP0ACQLET5xNv +NLAV28TDafBlxctqbrdHpSfiL+BplTYQvtljTkPfuVUt2bmLL5b3uxUJq8he+CKS1Af hHzQn56AoeyIq+geOe2OmUX0qSj1/EbFk0y0J3/0mCf46TsmVvZbVm4eQN0K+52KsiIA 9p9whG/6eIaypcqWH3282K0jOqOBu8fWmt96/Kq375ra9BpxqNHsuRxyY3OAdHgPE3vs xYQQ== X-Gm-Message-State: AOAM531fBJErIrpBHfEyjImR5IfTzZAjDDYHicKHsz1ud36auMDlxEoY RL6rwZScRnTR6/1DCXpAOUh4Znv89T5jNUOO5xJXpDdwjWCqiNhHYPAxPVz0aqFiEYND6LAeEpw jPKVMMwbhGjbOFnlz X-Received: by 2002:a17:906:4149:: with SMTP id l9mr2025941ejk.48.1606384573589; Thu, 26 Nov 2020 01:56:13 -0800 (PST) X-Google-Smtp-Source: ABdhPJxpwWVFyFaUq292qnGC1BLOcKdLXpzzdLATaHboam1LmcQEjYpWqGxMbDjjskkqrrnuIe1btQ== X-Received: by 2002:a17:906:4149:: with SMTP id l9mr2025917ejk.48.1606384573185; Thu, 26 Nov 2020 01:56:13 -0800 (PST) Received: from alrua-x1.borgediget.toke.dk ([2a0c:4d80:42:443::2]) by smtp.gmail.com with ESMTPSA id jr13sm2742167ejb.50.2020.11.26.01.56.12 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 26 Nov 2020 01:56:12 -0800 (PST) Received: by alrua-x1.borgediget.toke.dk (Postfix, from userid 1000) id 13A1E183064; Thu, 26 Nov 2020 10:56:12 +0100 (CET) From: Toke =?utf-8?Q?H=C3=B8iland-J=C3=B8rgensen?= To: Roman Gushchin , Daniel Borkmann Cc: bpf@vger.kernel.org, ast@kernel.org, netdev@vger.kernel.org, andrii@kernel.org, akpm@linux-foundation.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-team@fb.com, hannes@cmpxchg.org, tj@kernel.org Subject: Re: [PATCH bpf-next v8 06/34] bpf: prepare for memcg-based memory accounting for bpf maps In-Reply-To: <20201126023000.GB840171@carbon.dhcp.thefacebook.com> References: <20201125030119.2864302-1-guro@fb.com> <20201125030119.2864302-7-guro@fb.com> <20201126023000.GB840171@carbon.dhcp.thefacebook.com> X-Clacks-Overhead: GNU Terry Pratchett Date: Thu, 26 Nov 2020 10:56:12 +0100 Message-ID: <87lfeol9vn.fsf@toke.dk> MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org Roman Gushchin writes: > On Thu, Nov 26, 2020 at 01:21:41AM +0100, Daniel Borkmann wrote: >> On 11/25/20 4:00 AM, Roman Gushchin wrote: >> > In the absolute majority of cases if a process is making a kernel >> > allocation, it's memory cgroup is getting charged. >> > >> > Bpf maps can be updated from an interrupt context and in such >> > case there is no process which can be charged. It makes the memory >> > accounting of bpf maps non-trivial. >> > >> > Fortunately, after commit 4127c6504f25 ("mm: kmem: enable kernel >> > memcg accounting from interrupt contexts") and b87d8cefe43c >> > ("mm, memcg: rework remote charging API to support nesting") >> > it's finally possible. >> > >> > To do it, a pointer to the memory cgroup of the process, which created >> > the map, is saved, and this cgroup can be charged for all allocations >> > made from an interrupt context. This commit introduces 2 helpers: >> > bpf_map_kmalloc_node() and bpf_map_alloc_percpu(). They can be used in >> > the bpf code for accounted memory allocations, both in the process and >> > interrupt contexts. In the interrupt context they're using the saved >> > memory cgroup, otherwise the current cgroup is getting charged. >> > >> > Signed-off-by: Roman Gushchin >> >> Thanks for updating the cover letter; replying in this series instead >> on one more item that came to mind: >> >> [...] >> > diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c >> > index f3fe9f53f93c..4154c616788c 100644 >> > --- a/kernel/bpf/syscall.c >> > +++ b/kernel/bpf/syscall.c >> > @@ -31,6 +31,8 @@ >> > #include >> > #include >> > #include >> > +#include >> > +#include >> > #define IS_FD_ARRAY(map) ((map)->map_type == BPF_MAP_TYPE_PERF_EVENT_ARRAY || \ >> > (map)->map_type == BPF_MAP_TYPE_CGROUP_ARRAY || \ >> > @@ -456,6 +458,77 @@ void bpf_map_free_id(struct bpf_map *map, bool do_idr_lock) >> > __release(&map_idr_lock); >> > } >> > +#ifdef CONFIG_MEMCG_KMEM >> > +static void bpf_map_save_memcg(struct bpf_map *map) >> > +{ >> > + map->memcg = get_mem_cgroup_from_mm(current->mm); >> > +} >> > + >> > +static void bpf_map_release_memcg(struct bpf_map *map) >> > +{ >> > + mem_cgroup_put(map->memcg); >> > +} >> > + >> > +void *bpf_map_kmalloc_node(const struct bpf_map *map, size_t size, gfp_t flags, >> > + int node) >> > +{ >> > + struct mem_cgroup *old_memcg; >> > + bool in_interrupt; >> > + void *ptr; >> > + >> > + /* >> > + * If the memory allocation is performed from an interrupt context, >> > + * the memory cgroup to charge can't be determined from the context >> > + * of the current task. Instead, we charge the memory cgroup, which >> > + * contained the process created the map. >> > + */ >> > + in_interrupt = in_interrupt(); >> > + if (in_interrupt) >> > + old_memcg = set_active_memcg(map->memcg); >> > + >> > + ptr = kmalloc_node(size, flags, node); >> > + >> > + if (in_interrupt) >> > + set_active_memcg(old_memcg); >> > + >> > + return ptr; >> > +} >> > + >> > +void __percpu *bpf_map_alloc_percpu(const struct bpf_map *map, size_t size, >> > + size_t align, gfp_t gfp) >> > +{ >> > + struct mem_cgroup *old_memcg; >> > + bool in_interrupt; >> > + void *ptr; >> > + >> > + /* >> > + * If the memory allocation is performed from an interrupt context, >> > + * the memory cgroup to charge can't be determined from the context >> > + * of the current task. Instead, we charge the memory cgroup, which >> > + * contained the process created the map. >> > + */ >> > + in_interrupt = in_interrupt(); >> > + if (in_interrupt) >> > + old_memcg = set_active_memcg(map->memcg); >> > + >> > + ptr = __alloc_percpu_gfp(size, align, gfp); >> > + >> > + if (in_interrupt) >> > + set_active_memcg(old_memcg); >> >> For this and above bpf_map_kmalloc_node() one, wouldn't it make more sense to >> perform the temporary memcg unconditionally? >> >> old_memcg = set_active_memcg(map->memcg); >> ptr = kmalloc_node(size, flags, node); >> set_active_memcg(old_memcg); >> >> I think the semantics are otherwise a bit weird and the charging unpredictable; >> this way it would /always/ be accounted against the prog in the memcg that >> originally created the map. >> >> E.g. maps could be shared between progs attached to, say, XDP/tc where in_interrupt() >> holds true with progs attached to skb-cgroup/egress where we're still in process >> context. So some part of the memory is charged against the original map's memcg and >> some other part against the current process' memcg which seems odd, no? Or, for example, >> if we start to run a tracing BPF prog which updates state in a BPF map ... that tracing >> prog now interferes with processes in other memcgs which may not be intentional & could >> lead to potential failures there as opposed when the tracing prog is not run. My concern >> is that the semantics are not quite clear and behavior unpredictable compared to always >> charging against map->memcg. >> >> Similarly, what if an orchestration prog creates dedicated memcg(s) for maps with >> individual limits ... the assumed behavior (imho) would be that whatever memory is >> accounted on the map it can be accurately retrieved from there & similarly limits >> enforced, no? It seems that would not be the case currently. >> >> Thoughts? > > I did consider this option. There are pros and cons. In general we > tend to charge the cgroup which actually allocates the memory, and I > decided to stick with this rule. I agree, it's fairly easy to come > with arguments why always charging the map creator is better. The > opposite is also true: it's not clear why bpf is different here. So > I'm fine with both options, if there is a wide consensus, I'm happy to > switch to the other option. In general, I believe that the current > scheme is more flexible: if someone want to pay in advance, they are > free to preallocate the map. Otherwise it's up to whoever wants to > populate it. I think I agree with Daniel here: conceptually the memory used by a map ought to belong to that map's memcg. I can see how the other scheme can be more flexible, but as Daniel points out it seems like it can lead to hard-to-debug errors... (Side note: I'm really excited about this work in general! The ulimit thing has been a major pain...) -Toke