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=-5.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=no 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 AC3DCC2D0A3 for ; Mon, 9 Nov 2020 18:51:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 6A80D20578 for ; Mon, 9 Nov 2020 18:51:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729879AbgKISvo (ORCPT ); Mon, 9 Nov 2020 13:51:44 -0500 Received: from mx2.suse.de ([195.135.220.15]:43674 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729292AbgKISvo (ORCPT ); Mon, 9 Nov 2020 13:51:44 -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 9B3C3AB95; Mon, 9 Nov 2020 18:51:42 +0000 (UTC) Date: Mon, 9 Nov 2020 19:51:38 +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, 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 v3 09/21] mm/hugetlb: Free the vmemmap pages associated with each hugetlb page Message-ID: <20201109185138.GD17356@linux> References: <20201108141113.65450-1-songmuchun@bytedance.com> <20201108141113.65450-10-songmuchun@bytedance.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20201108141113.65450-10-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 Sun, Nov 08, 2020 at 10:11:01PM +0800, Muchun Song wrote: > +static inline int freed_vmemmap_hpage(struct page *page) > +{ > + return atomic_read(&page->_mapcount) + 1; > +} > + > +static inline int freed_vmemmap_hpage_inc(struct page *page) > +{ > + return atomic_inc_return_relaxed(&page->_mapcount) + 1; > +} > + > +static inline int freed_vmemmap_hpage_dec(struct page *page) > +{ > + return atomic_dec_return_relaxed(&page->_mapcount) + 1; > +} Are these relaxed any different that the normal ones on x86_64? I got confused following the macros. > +static void __free_huge_page_pte_vmemmap(struct page *reuse, pte_t *ptep, > + unsigned long start, > + unsigned int nr_free, > + struct list_head *free_pages) > +{ > + /* Make the tail pages are mapped read-only. */ > + pgprot_t pgprot = PAGE_KERNEL_RO; > + pte_t entry = mk_pte(reuse, pgprot); > + unsigned long addr; > + unsigned long end = start + (nr_free << PAGE_SHIFT); See below. > +static void __free_huge_page_pmd_vmemmap(struct hstate *h, pmd_t *pmd, > + unsigned long addr, > + struct list_head *free_pages) > +{ > + unsigned long next; > + unsigned long start = addr + RESERVE_VMEMMAP_NR * PAGE_SIZE; > + unsigned long end = addr + vmemmap_pages_size_per_hpage(h); > + struct page *reuse = NULL; > + > + addr = start; > + do { > + unsigned int nr_pages; > + pte_t *ptep; > + > + ptep = pte_offset_kernel(pmd, addr); > + if (!reuse) > + reuse = pte_page(ptep[-1]); Can we define a proper name for that instead of -1? e.g: TAIL_PAGE_REUSE or something like that. > + > + next = vmemmap_hpage_addr_end(addr, end); > + nr_pages = (next - addr) >> PAGE_SHIFT; > + __free_huge_page_pte_vmemmap(reuse, ptep, addr, nr_pages, > + free_pages); Why not passing next instead of nr_pages? I think it makes more sense. As a bonus we can kill the variable. > +static void split_vmemmap_huge_page(struct hstate *h, struct page *head, > + pmd_t *pmd) > +{ > + pgtable_t pgtable; > + unsigned long start = (unsigned long)head & VMEMMAP_HPAGE_MASK; > + unsigned long addr = start; > + unsigned int nr = pgtable_pages_to_prealloc_per_hpage(h); > + > + while (nr-- && (pgtable = vmemmap_pgtable_withdraw(head))) { The same with previous patches, I would scrap "nr" and its use. > + VM_BUG_ON(freed_vmemmap_hpage(pgtable)); I guess here we want to check whether we already call free_huge_page_vmemmap on this range? For this to have happened, the locking should have failed, right? > +static void free_huge_page_vmemmap(struct hstate *h, struct page *head) > +{ > + pmd_t *pmd; > + spinlock_t *ptl; > + LIST_HEAD(free_pages); > + > + if (!free_vmemmap_pages_per_hpage(h)) > + return; > + > + pmd = vmemmap_to_pmd(head); > + ptl = vmemmap_pmd_lock(pmd); > + if (vmemmap_pmd_huge(pmd)) { > + VM_BUG_ON(!pgtable_pages_to_prealloc_per_hpage(h)); I think that checking for free_vmemmap_pages_per_hpage is enough. In the end, pgtable_pages_to_prealloc_per_hpage uses free_vmemmap_pages_per_hpage. -- Oscar Salvador SUSE L3