From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id AD49817E8 for ; Fri, 18 Nov 2022 03:40:18 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1668742817; 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=D9t+eQY+6vN6Lit1lFbVtBnu7nOyqlyFk5Gp4Vgcr5w=; b=WfBmszoYxkaTODlL2jyRiK7apd11QyUJcD09XhPpmG8zjcgLbMsVQ8ca2/BmodFfzb8env RqjMemu0oskygimoi/sEWpJ/sEykp1VYhInMmPzHnRdjcPMUzKvPmtvSAobajpp5Z06zXk fznUJGb8Yxbjxm9s+VMlQbGWuEqVe74= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-144-RTLR-N2tOq-IDNWzLAIkOw-1; Thu, 17 Nov 2022 22:40:07 -0500 X-MC-Unique: RTLR-N2tOq-IDNWzLAIkOw-1 Received: from smtp.corp.redhat.com (int-mx10.intmail.prod.int.rdu2.redhat.com [10.11.54.10]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 6BFC5856507; Fri, 18 Nov 2022 03:40:07 +0000 (UTC) Received: from localhost (ovpn-12-17.pek2.redhat.com [10.72.12.17]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 54B45492B15; Fri, 18 Nov 2022 03:40:06 +0000 (UTC) Date: Fri, 18 Nov 2022 11:40:03 +0800 From: Baoquan He To: Dennis Zhou Cc: Vlastimil Babka , 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> Precedence: bulk X-Mailing-List: oe-kbuild-all@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 In-Reply-To: X-Scanned-By: MIMEDefang 3.1 on 10.11.54.10 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline On 11/17/22 at 11:23am, Dennis Zhou wrote: > 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.