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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 5310CC10F1D for ; Tue, 13 Dec 2022 14:57:08 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S235944AbiLMO5G (ORCPT ); Tue, 13 Dec 2022 09:57:06 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42410 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236063AbiLMO47 (ORCPT ); Tue, 13 Dec 2022 09:56:59 -0500 Received: from mail-pl1-x62c.google.com (mail-pl1-x62c.google.com [IPv6:2607:f8b0:4864:20::62c]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id E6A2E6379; Tue, 13 Dec 2022 06:56:58 -0800 (PST) Received: by mail-pl1-x62c.google.com with SMTP id l10so2291474plb.8; Tue, 13 Dec 2022 06:56:58 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:from:to:cc:subject:date:message-id:reply-to; bh=Kuc4nUgO/XR9/IXR1IzCd2vTu1wAL/qMjW/mLLbmkGc=; b=RrmKZVM4DTmK68kBoKwpnqT5fT6a+1ei0i+9pcHm4Y+cQ6tFbr7At3lqFX/Icu5syp lhopjPWl3gtV41Bncc6CU2dib/KKWyZLsgr33J60ZqRyneDLpa51o/m7tE4E9l2U40NS 81yTNjRrQNCy+sRgOgRmVV6ouQeWzBcewWzim0DW638skjvf+aLKvymdDtUsDkKJ5GsD 2atnpsiKPqTLe835f6RIL+DU6yyp9qLo+5duuOLRTiEZOnvuXHY7SdJEunwNQJo/ITYl qxTRLzce2YVzByweQlvhiRiw1IgBfHpkN7XjVitsmcowndoiqdv6nxFt1S6Wo+7PGVF4 5hbA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=in-reply-to:content-disposition:mime-version:references:message-id :subject:cc:to:from:date:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to; bh=Kuc4nUgO/XR9/IXR1IzCd2vTu1wAL/qMjW/mLLbmkGc=; b=5LSpS4zFbEPqfnVHtfAULLGvFfrVDnvxsdDZeQqDlphJZz9PUl03pETY5kKjSZyCPS tPRBd7efrPklWN8wAd3qA8R2oZb38ztS0G3ZHKp2IKCiBO9eTwgA4bLtmsiZ9d9VxnKK NKDLMocVfJp5K17nUvzLx2I9wT4HTxsa8nwV1X2DLxhTwXM15Vej4UgoMnQPUWSErkIu ++prPA1TPuq+f4RSdTPDpWgdywHaHAUZFx+dxnrBGS0dDt6fdXtO/qEZh0c24zosJ3vN vxOjujaJS/LhPX7xWClY0wRq2nBGw/BRi8FqIOmrWkQOOeiNuj6syWAKlk7sZPBzQ1Qe 0nlg== X-Gm-Message-State: ANoB5pkJ3mdVy6TabQeMGnRHGbXgHrr0nQyoDYQMBsA/jaM8KOEt+Dlh bIH5ye0pDorHVjKxFDGgYUo= X-Google-Smtp-Source: AA0mqf6g2cjc5+IZgzWap0jf6DlXtUAS3dfGI+3GOaE7ypcRhl+1saQte0QPwcFhrvzxoJynzD6vLA== X-Received: by 2002:a17:902:f54b:b0:188:5e99:d84f with SMTP id h11-20020a170902f54b00b001885e99d84fmr29273515plf.42.1670943418265; Tue, 13 Dec 2022 06:56:58 -0800 (PST) Received: from hyeyoo ([114.29.91.56]) by smtp.gmail.com with ESMTPSA id s12-20020a170902ea0c00b00189ac5a2340sm8570908plg.124.2022.12.13.06.56.52 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 13 Dec 2022 06:56:57 -0800 (PST) Date: Tue, 13 Dec 2022 23:56:49 +0900 From: Hyeonggon Yoo <42.hyeyoo@gmail.com> To: Yafang Shao Cc: Vlastimil Babka , ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org, kafai@fb.com, songliubraving@fb.com, yhs@fb.com, john.fastabend@gmail.com, kpsingh@kernel.org, sdf@google.com, haoluo@google.com, jolsa@kernel.org, tj@kernel.org, dennis@kernel.org, cl@linux.com, akpm@linux-foundation.org, penberg@kernel.org, rientjes@google.com, iamjoonsoo.kim@lge.com, roman.gushchin@linux.dev, linux-mm@kvack.org, bpf@vger.kernel.org, rcu@vger.kernel.org Subject: Re: [RFC PATCH bpf-next 0/9] mm, bpf: Add BPF into /proc/meminfo Message-ID: References: <20221212003711.24977-1-laoar.shao@gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org On Tue, Dec 13, 2022 at 07:52:42PM +0800, Yafang Shao wrote: > On Tue, Dec 13, 2022 at 1:54 AM Vlastimil Babka wrote: > > > > On 12/12/22 01:37, Yafang Shao wrote: > > > Currently there's no way to get BPF memory usage, while we can only > > > estimate the usage by bpftool or memcg, both of which are not reliable. > > > > > > - bpftool > > > `bpftool {map,prog} show` can show us the memlock of each map and > > > prog, but the memlock is vary from the real memory size. The memlock > > > of a bpf object is approximately > > > `round_up(key_size + value_size, 8) * max_entries`, > > > so 1) it can't apply to the non-preallocated bpf map which may > > > increase or decrease the real memory size dynamically. 2) the element > > > size of some bpf map is not `key_size + value_size`, for example the > > > element size of htab is > > > `sizeof(struct htab_elem) + round_up(key_size, 8) + round_up(value_size, 8)` > > > That said the differece between these two values may be very great if > > > the key_size and value_size is small. For example in my verifaction, > > > the size of memlock and real memory of a preallocated hash map are, > > > > > > $ grep BPF /proc/meminfo > > > BPF: 1026048 B <<< the size of preallocated memalloc pool > > > > > > (create hash map) > > > > > > $ bpftool map show > > > 3: hash name count_map flags 0x0 > > > key 4B value 4B max_entries 1048576 memlock 8388608B > > > > > > $ grep BPF /proc/meminfo > > > BPF: 84919344 B > > > > > > So the real memory size is $((84919344 - 1026048)) which is 83893296 > > > bytes while the memlock is only 8388608 bytes. > > > > > > - memcg > > > With memcg we only know that the BPF memory usage is less than > > > memory.usage_in_bytes (or memory.current in v2). Furthermore, we only > > > know that the BPF memory usage is less than $MemTotal if the BPF > > > object is charged into root memcg :) > > > > > > So we need a way to get the BPF memory usage especially there will be > > > more and more bpf programs running on the production environment. The > > > memory usage of BPF memory is not trivial, which deserves a new item in > > > /proc/meminfo. > > > > > > This patchset introduce a solution to calculate the BPF memory usage. > > > This solution is similar to how memory is charged into memcg, so it is > > > easy to understand. It counts three types of memory usage - > > > - page > > > via kmalloc, vmalloc, kmem_cache_alloc or alloc pages directly and > > > their families. > > > When a page is allocated, we will count its size and mark the head > > > page, and then check the head page at page freeing. > > > - slab > > > via kmalloc, kmem_cache_alloc and their families. > > > When a slab object is allocated, we will mark this object in this > > > slab and check it at slab object freeing. That said we need extra memory > > > to store the information of each object in a slab. > > > - percpu > > > via alloc_percpu and its family. > > > When a percpu area is allocated, we will mark this area in this > > > percpu chunk and check it at percpu area freeing. That said we need > > > extra memory to store the information of each area in a percpu chunk. > > > > > > So we only need to annotate the allcation to add the BPF memory size, > > > and the sub of the BPF memory size will be handled automatically at > > > freeing. We can annotate it in irq, softirq or process context. To avoid > > > counting the nested allcations, for example the percpu backing allocator, > > > we reuse the __GFP_ACCOUNT to filter them out. __GFP_ACCOUNT also make > > > the count consistent with memcg accounting. > > > > So you can't easily annotate the freeing places as well, to avoid the whole > > tracking infrastructure? > > The trouble is kfree_rcu(). for example, > old_item = active_vm_item_set(ACTIVE_VM_BPF); > kfree_rcu(); > active_vm_item_set(old_item); > If we want to pass the ACTIVE_VM_BPF into the deferred rcu context, we > will change lots of code in the RCU subsystem. I'm not sure if it is > worth it. (+Cc rcu folks) IMO adding new kfree_rcu() varient for BPF that accounts BPF memory usage would be much less churn :) > > > I thought there was a patchset for a whole > > bfp-specific memory allocator, where accounting would be implemented > > naturally, I would imagine. > > > > I posted a patchset[1] which annotates both allocating and freeing > several months ago. > But unfortunately after more investigation and verification I found > the deferred freeing context is a problem, which can't be resolved > easily. > That's why I finally decided to annotate allocating only. > > [1]. https://lore.kernel.org/linux-mm/20220921170002.29557-1-laoar.shao@gmail.com/ > > > > To store the information of a slab or a page, we need to create a new > > > member in struct page, but we can do it in page extension which can > > > avoid changing the size of struct page. So a new page extension > > > active_vm is introduced. Each page and each slab which is allocated as > > > BPF memory will have a struct active_vm. The reason it is named as > > > active_vm is that we can extend it to other areas easily, for example in > > > the future we may use it to count other memory usage. > > > > > > The new page extension active_vm can be disabled via CONFIG_ACTIVE_VM at > > > compile time or kernel parameter `active_vm=` at runtime. > > > > The issue with page_ext is the extra memory usage, so it was rather intended > > for debugging features that can be always compiled in, but only enabled at > > runtime when debugging is needed. The overhead is only paid when enabled. > > That's at least the case of page_owner and page_table_check. The 32bit > > page_idle is rather an oddity that could have instead stayed 64-bit only. > > > > Right, it seems currently page_ext is for debugging purposes only. > > > But this is proposing a page_ext functionality supposed to be enabled at all > > times in production, with the goal of improved accounting. Not an on-demand > > debugging. I'm afraid the costs will outweight the benefits. > > > > The memory overhead of this new page extension is (8/4096), which is > 0.2% of total memory. Not too big to be acceptable. It's generally unacceptable to increase sizeof(struct page) (nor enabling page_ext by default, and that's the why page_ext is for debugging purposes only) > If the user really > thinks this overhead is not accepted, he can set "active_vm=off" to > disable it. I'd say many people won't welcome adding 0.2% of total memory by default to get BPF memory usage. > To reduce the memory overhead further, I have a bold idea. > Actually we don't need to allocate such a page extension for every > page, while we only need to allocate it if the user needs to access > it. That said it seems that we can allocate some kind of page > extensions dynamically rather than preallocate at booting, but I > haven't investigated it deeply to check if it can work. What do you > think? > > > Just a quick thought, in case the bpf accounting really can't be handled > > without marking pages and slab objects - since memcg already has hooks there > > without need of page_ext, couldn't it be done by extending the memcg infra > > instead? > > > > We need to make sure the accounting of BPF memory usage is still > workable even without memcg, see also the previous discussion[2]. > > [2]. https://lore.kernel.org/linux-mm/Yy53cgcwx+hTll4R@slm.duckdns.org/ -- Thanks, Hyeonggon