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=-5.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI, SPF_HELO_NONE,SPF_PASS 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 1A583C433DB for ; Mon, 15 Feb 2021 12:22:56 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id D8BB664D9D for ; Mon, 15 Feb 2021 12:22:55 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230364AbhBOMWr (ORCPT ); Mon, 15 Feb 2021 07:22:47 -0500 Received: from mx2.suse.de ([195.135.220.15]:51962 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230182AbhBOMTX (ORCPT ); Mon, 15 Feb 2021 07:19:23 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=suse.com; s=susede1; t=1613391510; h=from:from:reply-to:date:date:message-id:message-id:to:to:cc:cc: mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=x1iUlQtCie5/gwEyMBhP30W+W9DhXIzHbKFBfoEa56E=; b=V0DbYkTwiM0tOl26vhP1L8rp/pP++Dy2XOonRrDp/kKu62rdJ2gCYXHBa1liNzw61St7f2 jDIGrhNWlxKk9IAxrvXVQxxGvcFG86aFLMFfoS7hnFwdj7eIco/wvFayXKayqbf/ZXqyq0 ktBdZpk73jL35bfB/SXuYdsui3QsqKs= Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 20F71AC32; Mon, 15 Feb 2021 12:18:30 +0000 (UTC) Date: Mon, 15 Feb 2021 13:18:28 +0100 From: Michal Hocko To: Muchun Song Cc: Jonathan Corbet , Mike Kravetz , Thomas Gleixner , mingo@redhat.com, bp@alien8.de, x86@kernel.org, hpa@zytor.com, dave.hansen@linux.intel.com, luto@kernel.org, Peter Zijlstra , viro@zeniv.linux.org.uk, Andrew Morton , paulmck@kernel.org, mchehab+huawei@kernel.org, pawan.kumar.gupta@linux.intel.com, Randy Dunlap , oneukum@suse.com, anshuman.khandual@arm.com, jroedel@suse.de, Mina Almasry , David Rientjes , Matthew Wilcox , Oscar Salvador , "Song Bao Hua (Barry Song)" , David Hildenbrand , HORIGUCHI =?utf-8?B?TkFPWUEo5aCA5Y+jIOebtOS5nyk=?= , Joao Martins , Xiongchun duan , linux-doc@vger.kernel.org, LKML , Linux Memory Management List , linux-fsdevel Subject: Re: [External] Re: [PATCH v15 4/8] mm: hugetlb: alloc the vmemmap pages associated with each HugeTLB page Message-ID: References: <20210208085013.89436-1-songmuchun@bytedance.com> <20210208085013.89436-5-songmuchun@bytedance.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon 15-02-21 20:00:07, Muchun Song wrote: > On Mon, Feb 15, 2021 at 7:51 PM Muchun Song wrote: > > > > On Mon, Feb 15, 2021 at 6:33 PM Michal Hocko wrote: > > > > > > On Mon 15-02-21 18:05:06, Muchun Song wrote: > > > > On Fri, Feb 12, 2021 at 11:32 PM Michal Hocko wrote: > > > [...] > > > > > > +int alloc_huge_page_vmemmap(struct hstate *h, struct page *head) > > > > > > +{ > > > > > > + int ret; > > > > > > + unsigned long vmemmap_addr = (unsigned long)head; > > > > > > + unsigned long vmemmap_end, vmemmap_reuse; > > > > > > + > > > > > > + if (!free_vmemmap_pages_per_hpage(h)) > > > > > > + return 0; > > > > > > + > > > > > > + vmemmap_addr += RESERVE_VMEMMAP_SIZE; > > > > > > + vmemmap_end = vmemmap_addr + free_vmemmap_pages_size_per_hpage(h); > > > > > > + vmemmap_reuse = vmemmap_addr - PAGE_SIZE; > > > > > > + > > > > > > + /* > > > > > > + * The pages which the vmemmap virtual address range [@vmemmap_addr, > > > > > > + * @vmemmap_end) are mapped to are freed to the buddy allocator, and > > > > > > + * the range is mapped to the page which @vmemmap_reuse is mapped to. > > > > > > + * When a HugeTLB page is freed to the buddy allocator, previously > > > > > > + * discarded vmemmap pages must be allocated and remapping. > > > > > > + */ > > > > > > + ret = vmemmap_remap_alloc(vmemmap_addr, vmemmap_end, vmemmap_reuse, > > > > > > + GFP_ATOMIC | __GFP_NOWARN | __GFP_THISNODE); > > > > > > > > > > I do not think that this is a good allocation mode. GFP_ATOMIC is a non > > > > > sleeping allocation and a medium memory pressure might cause it to > > > > > fail prematurely. I do not think this is really an atomic context which > > > > > couldn't afford memory reclaim. I also do not think we want to grant > > > > > > > > Because alloc_huge_page_vmemmap is called under hugetlb_lock > > > > now. So using GFP_ATOMIC indeed makes the code more simpler. > > > > > > You can have a preallocated list of pages prior taking the lock. > > > > A discussion about this can refer to here: > > > > https://patchwork.kernel.org/project/linux-mm/patch/20210117151053.24600-5-songmuchun@bytedance.com/ > > > > > Moreover do we want to manipulate vmemmaps from under spinlock in > > > general. I have to say I have missed that detail when reviewing. Need to > > > think more. > > > > > > > From the document of the kernel, I learned that __GFP_NOMEMALLOC > > > > can be used to explicitly forbid access to emergency reserves. So if > > > > we do not want to use the reserve memory. How about replacing it to > > > > > > > > GFP_ATOMIC | __GFP_NOMEMALLOC | __GFP_NOWARN | __GFP_THISNODE > > > > > > The whole point of GFP_ATOMIC is to grant access to memory reserves so > > > the above is quite dubious. If you do not want access to memory reserves > > > > Look at the code of gfp_to_alloc_flags(). > > > > static inline unsigned int gfp_to_alloc_flags(gfp_t gfp_mask) > > { > > [...] > > if (gfp_mask & __GFP_ATOMIC) { > > /* > > * Not worth trying to allocate harder for __GFP_NOMEMALLOC even > > * if it can't schedule. > > */ > > if (!(gfp_mask & __GFP_NOMEMALLOC)) > > alloc_flags |= ALLOC_HARDER; > > [...] > > } > > > > Seems to allow this operation (GFP_ATOMIC | __GFP_NOMEMALLOC). Please read my response again more carefully. I am not claiming that combination is not allowed. I have said it doesn't make any sense in this context. -- Michal Hocko SUSE Labs