From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-oi0-f69.google.com (mail-oi0-f69.google.com [209.85.218.69]) by kanga.kvack.org (Postfix) with ESMTP id 799766B0253 for ; Tue, 3 Oct 2017 18:29:52 -0400 (EDT) Received: by mail-oi0-f69.google.com with SMTP id n82so2883904oig.22 for ; Tue, 03 Oct 2017 15:29:52 -0700 (PDT) Received: from mail-sor-f41.google.com (mail-sor-f41.google.com. [209.85.220.41]) by mx.google.com with SMTPS id q10sor11018113qtk.10.2017.10.03.15.29.51 for (Google Transport Security); Tue, 03 Oct 2017 15:29:51 -0700 (PDT) Date: Tue, 3 Oct 2017 18:29:49 -0400 (EDT) From: Nicolas Pitre Subject: Re: [PATCH] mm/percpu.c: use smarter memory allocation for struct pcpu_alloc_info In-Reply-To: <20171003210540.GM3301751@devbig577.frc2.facebook.com> Message-ID: References: <20171003210540.GM3301751@devbig577.frc2.facebook.com> MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Sender: owner-linux-mm@kvack.org List-ID: To: Tejun Heo Cc: Christoph Lameter , linux-mm@kvack.org, linux-kernel@vger.kernel.org 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 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); } #endif /* CONFIG_SMP */ -- 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