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=-8.8 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS 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 636D3C4361B for ; Thu, 10 Dec 2020 14:57:29 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 29AD3206D5 for ; Thu, 10 Dec 2020 14:57:29 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2389663AbgLJOvB (ORCPT ); Thu, 10 Dec 2020 09:51:01 -0500 Received: from mx2.suse.de ([195.135.220.15]:50308 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2391041AbgLJOnm (ORCPT ); Thu, 10 Dec 2020 09:43:42 -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 A76BCAE87; Thu, 10 Dec 2020 14:43:00 +0000 (UTC) Date: Thu, 10 Dec 2020 15:42:56 +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 04/12] mm/hugetlb: Free the vmemmap pages associated with each HugeTLB page Message-ID: <20201210144256.GB8538@localhost.localdomain> References: <20201210035526.38938-1-songmuchun@bytedance.com> <20201210035526.38938-5-songmuchun@bytedance.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201210035526.38938-5-songmuchun@bytedance.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Dec 10, 2020 at 11:55:18AM +0800, Muchun Song wrote: > The free_vmemmap_pages_per_hpage() which indicate that how many vmemmap > pages associated with a HugeTLB page that can be freed to the buddy > allocator just returns zero now, because all infrastructure is not > ready. Once all the infrastructure is ready, we will rework this > function to support the feature. I would reword the above to: "free_vmemmap_pages_per_hpage(), which indicates how many vmemmap pages associated with a HugeTLB page can be freed, returns zero for now, which means the feature is disabled. We will enable it once all the infrastructure is there." Or something along those lines. > Signed-off-by: Muchun Song Overall this looks good to me, and it has seen a considerable simplification, which is good. Some nits/questions below: > +#define vmemmap_hpage_addr_end(addr, end) \ > +({ \ > + unsigned long __boundary; \ > + __boundary = ((addr) + VMEMMAP_HPAGE_SIZE) & VMEMMAP_HPAGE_MASK; \ > + (__boundary - 1 < (end) - 1) ? __boundary : (end); \ > +}) Maybe add a little comment explaining what are you trying to get here. > +/* > + * Walk a vmemmap address to the pmd it maps. > + */ > +static pmd_t *vmemmap_to_pmd(unsigned long addr) > +{ > + pgd_t *pgd; > + p4d_t *p4d; > + pud_t *pud; > + pmd_t *pmd; > + > + pgd = pgd_offset_k(addr); > + if (pgd_none(*pgd)) > + return NULL; > + > + p4d = p4d_offset(pgd, addr); > + if (p4d_none(*p4d)) > + return NULL; > + > + pud = pud_offset(p4d, addr); > + if (pud_none(*pud)) > + return NULL; > + > + pmd = pmd_offset(pud, addr); > + if (pmd_none(*pmd)) > + return NULL; > + > + return pmd; > +} I saw that some people suggested to put all the non-hugetlb vmemmap functions under sparsemem-vmemmap.c, which makes some sense if some feature is going to re-use this code somehow. (I am not sure if the recent patches that take advantage of this feature for ZONE_DEVICE needs something like this). I do not have a strong opinion on this though. > +static void vmemmap_reuse_pte_range(struct page *reuse, pte_t *pte, > + unsigned long start, unsigned long end, > + struct list_head *vmemmap_pages) > +{ > + /* > + * Make the tail pages are mapped with read-only to catch > + * illegal write operation to the tail pages. > + */ > + pgprot_t pgprot = PAGE_KERNEL_RO; > + pte_t entry = mk_pte(reuse, pgprot); > + unsigned long addr; > + > + for (addr = start; addr < end; addr += PAGE_SIZE, pte++) { > + struct page *page; > + > + VM_BUG_ON(pte_none(*pte)); If it is none, page will be NULL and we will crash in the list_add below? > +static void vmemmap_remap_range(unsigned long start, unsigned long end, > + struct list_head *vmemmap_pages) > +{ > + pmd_t *pmd; > + unsigned long next, addr = start; > + struct page *reuse = NULL; > + > + VM_BUG_ON(!IS_ALIGNED(start, PAGE_SIZE)); > + VM_BUG_ON(!IS_ALIGNED(end, PAGE_SIZE)); > + VM_BUG_ON((start >> PUD_SHIFT) != (end >> PUD_SHIFT)); This last VM_BUG_ON, is to see if both fall under the same PUD table? > + > + pmd = vmemmap_to_pmd(addr); > + BUG_ON(!pmd); Which is the criteria you followed to make this BUG_ON and VM_BUG_ON in the check from vmemmap_reuse_pte_range? -- Oscar Salvador SUSE L3