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 X-Spam-Level: X-Spam-Status: No, score=-10.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 9DA69C433FE for ; Fri, 11 Dec 2020 09:37:03 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 4E81323F38 for ; Fri, 11 Dec 2020 09:37:03 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2437486AbgLKJgd (ORCPT ); Fri, 11 Dec 2020 04:36:33 -0500 Received: from mx2.suse.de ([195.135.220.15]:37926 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2405660AbgLKJgL (ORCPT ); Fri, 11 Dec 2020 04:36:11 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 24555AC10; Fri, 11 Dec 2020 09:35:28 +0000 (UTC) Date: Fri, 11 Dec 2020 10:35:23 +0100 From: Oscar Salvador To: Muchun Song Cc: corbet@lwn.net, mike.kravetz@oracle.com, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, x86@kernel.org, hpa@zytor.com, dave.hansen@linux.intel.com, luto@kernel.org, peterz@infradead.org, viro@zeniv.linux.org.uk, akpm@linux-foundation.org, paulmck@kernel.org, mchehab+huawei@kernel.org, pawan.kumar.gupta@linux.intel.com, rdunlap@infradead.org, oneukum@suse.com, anshuman.khandual@arm.com, jroedel@suse.de, almasrymina@google.com, rientjes@google.com, willy@infradead.org, mhocko@suse.com, song.bao.hua@hisilicon.com, david@redhat.com, duanxiongchun@bytedance.com, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org Subject: Re: [PATCH v8 06/12] mm/hugetlb: Allocate the vmemmap pages associated with each HugeTLB page Message-ID: <20201211093517.GA22210@linux> References: <20201210035526.38938-1-songmuchun@bytedance.com> <20201210035526.38938-7-songmuchun@bytedance.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201210035526.38938-7-songmuchun@bytedance.com> User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Thu, Dec 10, 2020 at 11:55:20AM +0800, Muchun Song wrote: > When we free a HugeTLB page to the buddy allocator, we should allocate the > vmemmap pages associated with it. We can do that in the __free_hugepage() "vmemmap pages that describe the range" would look better to me, but it is ok. > +#define GFP_VMEMMAP_PAGE \ > + (GFP_KERNEL | __GFP_RETRY_MAYFAIL | __GFP_HIGH | __GFP_NOWARN) > > #ifndef VMEMMAP_HPAGE_SHIFT > #define VMEMMAP_HPAGE_SHIFT HPAGE_SHIFT > @@ -197,6 +200,11 @@ > (__boundary - 1 < (end) - 1) ? __boundary : (end); \ > }) > > +typedef void (*vmemmap_remap_pte_func_t)(struct page *reuse, pte_t *pte, > + unsigned long start, unsigned long end, > + void *priv); Any reason to not have defined GFP_VMEMMAP_PAGE and the new typedef into hugetlb_vmemmap.h? > +static void vmemmap_restore_pte_range(struct page *reuse, pte_t *pte, > + unsigned long start, unsigned long end, > + void *priv) > +{ > + pgprot_t pgprot = PAGE_KERNEL; > + void *from = page_to_virt(reuse); > + unsigned long addr; > + struct list_head *pages = priv; [...] > + > + /* > + * Make sure that any data that writes to the @to is made > + * visible to the physical page. > + */ > + flush_kernel_vmap_range(to, PAGE_SIZE); Correct me if I am wrong, but flush_kernel_vmap_range is a NOOP under arches which do not have ARCH_HAS_FLUSH_KERNEL_DCACHE_PAGE. Since we only enable support for x86_64, and x86_64 is one of those arches, could we remove this, and introduced later on in case we enable this feature on an arch that needs it? I am not sure if you need to flush the range somehow, as you did in vmemmap_remap_range. > +retry: > + page = alloc_page(GFP_VMEMMAP_PAGE); > + if (unlikely(!page)) { > + msleep(100); > + /* > + * We should retry infinitely, because we cannot > + * handle allocation failures. Once we allocate > + * vmemmap pages successfully, then we can free > + * a HugeTLB page. > + */ > + goto retry; I think this is the trickiest part. With 2MB HugeTLB pages we only need 6 pages, but with 1GB, the number of pages we need to allocate increases significantly (4088 pages IIRC). And you are using __GFP_HIGH, which will allow us to use more memory (by cutting down the watermark), but it might lead to putting the system on its knees wrt. memory. And yes, I know that once we allocate the 4088 pages, 1GB gets freed, but still. I would like to hear Michal's thoughts on this one, but I wonder if it makes sense to not let 1GB-HugeTLB pages be freed. -- Oscar Salvador SUSE L3