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Thu, 17 Nov 2022 11:23:12 -0800 (PST) Received: from fedora ([2607:f598:b99a:be1:dfa7:eed0:45ca:de3c]) by smtp.gmail.com with ESMTPSA id e22-20020a635456000000b00477078686a9sm1358130pgm.42.2022.11.17.11.23.10 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 17 Nov 2022 11:23:11 -0800 (PST) Date: Thu, 17 Nov 2022 11:23:09 -0800 From: Dennis Zhou To: Baoquan He , Vlastimil Babka Cc: kernel test robot , oe-kbuild-all@lists.linux.dev, Linux Memory Management List , 42.hyeyoo@gmail.com Subject: Re: [linux-next:master 5002/7443] include/linux/compiler_types.h:357:45: error: call to '__compiletime_assert_474' declared with attribute error: BUILD_BUG_ON failed: PERCPU_DYNAMIC_EARLY_SIZE < NR_KMALLOC_TYPES * KMALLOC_SHIFT_HIGH * sizeof(struct kmem_cache_cpu) Message-ID: References: <202211120436.HzD1i2yQ-lkp@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1668712994; 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dkim=none; dmarc=fail reason="SPF not aligned (relaxed), No valid DKIM" header.from=kernel.org (policy=none); spf=pass (imf06.hostedemail.com: domain of dennisszhou@gmail.com designates 209.85.216.50 as permitted sender) smtp.mailfrom=dennisszhou@gmail.com X-Rspam-User: X-Stat-Signature: 5gxxaid9z8ojux4pjhib1z7uofscyz8b X-Rspamd-Queue-Id: 0860E180007 X-Rspamd-Server: rspam11 X-HE-Tag: 1668712993-465112 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Wed, Nov 16, 2022 at 07:32:03PM +0800, Baoquan He wrote: > On 11/15/22 at 12:00pm, Dennis Zhou wrote: > > On Tue, Nov 15, 2022 at 05:08:52PM +0800, Baoquan He wrote: > > > Hi Dennis, > > > > > > On 11/14/22 at 08:13pm, Dennis Zhou wrote: > > > > Hi Vlastimil & Baoquan, > > > > > > > > On Mon, Nov 14, 2022 at 06:58:13PM +0100, Vlastimil Babka wrote: > > > > > On 11/14/22 08:44, Baoquan He wrote: > > > > > > Hi, > > > > > > > > > > > > I reproduced the build failure according to lkp report and made a patch > > > > > > as below to fix it. > > > > > > > > > > > > From dae7dd9705015ce36db757e88c78802584f949b1 Mon Sep 17 00:00:00 2001 > > > > > > From: Baoquan He > > > > > > Date: Sun, 13 Nov 2022 18:08:27 +0800 > > > > > > Subject: [PATCH] percpu: adjust the value of PERCPU_DYNAMIC_EARLY_SIZE > > > > > > Content-type: text/plain > > > > > > > > > > > > LKP reported a build failure as below on the patch "mm/slub, percpu: > > > > > > correct the calculation of early percpu allocation size" > > > > > > > > > > Since I have that patch in slab.git exposed to -next, should I take this fix > > > > > too, to make things simpler? Dennis? > > > > > > > > > > > > > I don't have any problems with you running a fix, but I'm not quite sure > > > > this is the right fix. Though this might cause a trivial merge conflict > > > > with: d667c94962c1 ("mm/percpu: remove unused PERCPU_DYNAMIC_EARLY_SLOTS") > > > > in my percpu#for-6.2 branch. > > > > > > > > If I'm understanding this correctly, slub requires additional percpu > > > > memory due to the use of 64k pages. By increasing > > > > PERCPU_DYNAMIC_EARLY_SIZE, we solve the problem for 64k page users, but > > > > require a few unnecessary pages that can bloat the size of subsequent > > > > percpu chunks. Though, I'm not sure if that's an issue today for > > > > embedded devices. > > > > > > Thanks for looking into this. > > > > > > I guess you are talking about PERCPU_DYNAMIC_EARLY_SIZE will impact the > > > first dynamic chunk size of page first chunk, because the embed first > > > chunk will take PERCPU_DYNAMIC_RESERVE. And the impact is done in below > > > max() invacation. > > > > > > static struct pcpu_alloc_info * __init __flatten pcpu_build_alloc_info( > > > size_t reserved_size, size_t dyn_size, > > > size_t atom_size, > > > pcpu_fc_cpu_distance_fn_t cpu_distance_fn) > > > { > > > ...... > > > /* calculate size_sum and ensure dyn_size is enough for early alloc */ > > > size_sum = PFN_ALIGN(static_size + reserved_size + > > > max_t(size_t, dyn_size, PERCPU_DYNAMIC_EARLY_SIZE)); > > > ...... > > > } > > > > > > > > > > > I think adding parity to PERCPU_DYNAMIC_EARLY_SIZE with > > > > PERCPU_DYNAMIC_RESERVE is defined by BITS_PER_LONG is a safer option > > > > here. A small TODO item would be to make PERCPU_DYNAMIC_RESERVE be a + > > > > value instead of a max() with PERCPU_DYNAMIC_EARLY_SIZE. > > > > > > Hmm, the below change may not take power arch into account. Please > > > check arch/powerpc/include/asm/page.h, seems the 32bit ppc could have > > > 256K pages too. Adding PERCPU_DYNAMIC_EARLY_SIZE to 20K may cost extra > > > memory during boot. But th left space of 1st dynamic chunk will join > > > the later percpu dynamic allocation, it's not wasted, right? > > > > > > Not sure if I got your point. > > > > > > > > > > Ah, I'm not familiar with all the PAGE_SIZE and word length > > combinations. > > > > The first chunk is smaller in the embedded case with the assumption that > > static percpu variables are highly accessed along with the limited > > initial allocations. While adding an additional 8KB is not the biggest > > deal to the first chunk, this can cause the unit_size for subsequent > > chunks to be larger. For example, x86 unit size jumps in powers of 2 due > > to alignment and packing against an allocation size of 2MB. So if we're > > at say 60KB for the first chunk, subsequent chunks could be 64KB. But > > adding 8KB, we'd go from 60KB -> 68KB and a chunk size of 64KB -> 128KB. > > I could have misunderstanding about the first chunk usage and percpu > code. Below is my personal uderstanding about the 1st chunk size and > how PERCPU_DYNAMIC_EARLY_SIZE could impact it, please help point out > if I am wrong. > > ~~~ > Abstract the definition of them here for reference. > /* > * Percpu allocator can serve percpu allocations before slab is > * initialized which allows slab to depend on the percpu allocator. > * The following parameter decide how much resource to preallocate > * for this. Keep PERCPU_DYNAMIC_RESERVE equal to or larger than > ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > * PERCPU_DYNAMIC_EARLY_SIZE. > ~~~~~~~~~~~~~~~~~~~~~ > */ > #define PERCPU_DYNAMIC_EARLY_SIZE (12 << 10) > ...... > #if BITS_PER_LONG > 32 > #define PERCPU_DYNAMIC_RESERVE (28 << 10) > #else > #define PERCPU_DYNAMIC_RESERVE (20 << 10) > #endif > > From above definition, we can see that no matter how big > PERCPU_DYNAMIC_RESERVE is , it's >= PERCPU_DYNAMIC_EARLY_SIZE as the > code comment says. So the max() in pcpu_build_alloc_info() won't impact > the embeded 1st chunk at all. > > So, PERCPU_DYNAMIC_EARLY_SIZE can only impact the page 1st chunk case, > namely when calling pcpu_page_first_chunk() to do that. In > pcpu_page_first_chunk(), we don't provide dyn_size, so with the help of > max(), it will get final dyn_size as PERCPU_DYNAMIC_EARLY_SIZE. This is > the only place where PERCPU_DYNAMIC_EARLY_SIZE takes effect on percpu. > However, the atom size of page 1st chunk is PAGE_SIZE, it doesn't have > the issue of possible bloating unit_size by the atom size, e.g 2M on > x86_64. Since pcpu_page_first_chunk() is the fallback of > pcpu_embed_first_chunk(), if we decide to provide PERCPU_DYNAMIC_RESERVE > as the current value, why we grudge setting it as the smaller value, > 20K, whether it's 32bit or 64bit. > I think I might be overindexing on the out of tree modifications here. Currently, I think it's clear how modifying PERCPU_DYNAMIC_RESERVE affects the system with the lower bound being dictated by PERCPU_DYNAMIC_EARLY_SIZE. If we bump PERCPU_DYNAMIC_EARLY_SIZE, it's not inherently obvious you can drop that value lower depending on your system config. Ultimately, it is only a few pages, so is saving it that big of a deal today? Likely not, just a bit wasteful to potentially orphan a few extra pages unnecessarily. Let's just fix this now and I can massage this in the future if anything comes up. I appreciate you taking the time to have this discussion with me. Vlastimil, can you please pick up this fix. Acked-by: Dennis Zhou Thanks, Dennis > > > > > If not `BITS_PER_LONG >32`, we could do `PAGE_SHIFT > 12`. > > > > Thanks, > > Dennis > > > > > > > > > > --- > > > > diff --git a/include/linux/percpu.h b/include/linux/percpu.h > > > > index f1ec5ad1351c..22ce3271eed2 100644 > > > > --- a/include/linux/percpu.h > > > > +++ b/include/linux/percpu.h > > > > @@ -42,7 +42,11 @@ > > > > * larger than PERCPU_DYNAMIC_EARLY_SIZE. > > > > */ > > > > #define PERCPU_DYNAMIC_EARLY_SLOTS 128 > > > > +#if BITS_PER_LONG > 32 > > > > +#define PERCPU_DYNAMIC_EARLY_SIZE (20 << 10) > > > > +#else > > > > #define PERCPU_DYNAMIC_EARLY_SIZE (12 << 10) > > > > +#endif > > > > > > > > /* > > > > * PERCPU_DYNAMIC_RESERVE indicates the amount of free area to piggy > > > > > > > > > > > > > >