From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-pg0-f70.google.com (mail-pg0-f70.google.com [74.125.83.70]) by kanga.kvack.org (Postfix) with ESMTP id 8A85C6B0038 for ; Sat, 18 Nov 2017 13:25:51 -0500 (EST) Received: by mail-pg0-f70.google.com with SMTP id r12so5542381pgu.9 for ; Sat, 18 Nov 2017 10:25:51 -0800 (PST) Received: from mail-sor-f65.google.com (mail-sor-f65.google.com. [209.85.220.65]) by mx.google.com with SMTPS id x12sor1582081plv.65.2017.11.18.10.25.49 for (Google Transport Security); Sat, 18 Nov 2017 10:25:49 -0800 (PST) Date: Sat, 18 Nov 2017 10:25:42 -0800 From: Guenter Roeck Subject: Re: mm/percpu.c: use smarter memory allocation for struct pcpu_alloc_info (crisv32 hang) Message-ID: <20171118182542.GA23928@roeck-us.net> References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: owner-linux-mm@kvack.org List-ID: To: Nicolas Pitre Cc: Tejun Heo , Christoph Lameter , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Mikael Starvik , Jesper Nilsson , linux-cris-kernel@axis.com Hi, On Tue, Oct 03, 2017 at 06:29:49PM -0400, Nicolas Pitre wrote: > On Tue, 3 Oct 2017, Tejun Heo wrote: > > > On Tue, Oct 03, 2017 at 04:57:44PM -0400, Nicolas Pitre wrote: > > > This can be much smaller than a page on very small memory systems. > > > Always rounding up the size to a page is wasteful in that case, and > > > required alignment is smaller than the memblock default. Let's round > > > things up to a page size only when the actual size is >= page size, and > > > then it makes sense to page-align for a nicer allocation pattern. > > > > Isn't that a temporary area which gets freed later during boot? > > Hmmm... > > It may get freed through 3 different paths where 2 of them are error > paths. What looks like a non-error path is in pcpu_embed_first_chunk() > called from setup_per_cpu_areas(). But there are two versions of > setup_per_cpu_areas(): one for SMP and one for !SMP. And the !SMP case > never calls pcpu_free_alloc_info() currently. > > I'm not sure i understand that code fully, but maybe the following patch > could be a better fit: > > ----- >8 > Subject: [PATCH] percpu: don't forget to free the temporary struct pcpu_alloc_info > > Unlike the SMP case, the !SMP case does not free the memory for struct > pcpu_alloc_info allocated in setup_per_cpu_areas(). And to give it a > chance of being reused by the page allocator later, align it to a page > boundary just like its size. > > Signed-off-by: Nicolas Pitre This patch causes my crisv32 qemu emulation to hang with no console output. > > diff --git a/mm/percpu.c b/mm/percpu.c > index 434844415d..caab63375b 100644 > --- a/mm/percpu.c > +++ b/mm/percpu.c > @@ -1416,7 +1416,7 @@ struct pcpu_alloc_info * __init pcpu_alloc_alloc_info(int nr_groups, > __alignof__(ai->groups[0].cpu_map[0])); > ai_size = base_size + nr_units * sizeof(ai->groups[0].cpu_map[0]); > > - ptr = memblock_virt_alloc_nopanic(PFN_ALIGN(ai_size), 0); > + ptr = memblock_virt_alloc_nopanic(PFN_ALIGN(ai_size), PAGE_SIZE); > if (!ptr) > return NULL; > ai = ptr; > @@ -2295,6 +2295,7 @@ void __init setup_per_cpu_areas(void) > > if (pcpu_setup_first_chunk(ai, fc) < 0) > panic("Failed to initialize percpu areas."); > + pcpu_free_alloc_info(ai); This is the culprit. Everything works fine if I remove this line. No idea if the problem is here or in the cris core. Copying cris maintainers for input. Guenter -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org