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Mon, 15 Feb 2021 12:24:47 +0000 (UTC) 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=1613391886; 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=clNVAPUhMB6rr4TBZ1GcOTiKp+wPJNTpI9l+37a26XA=; b=dp0V06WWkqe+uRmlRdGyLDWQqXtP25DEndHfYdVJ2FhTZuSE6X2UmRn0rNX1CHZgX76/Ze Daq8252M97ty2PmdemtbniFK7GVBOHJo2qki6iDlMEnHSGKIOLqy/pzsUOC2d9khg6yRqt xvqicVpi2h3jtm7hdubVWtDU36hRhzs= Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id E9374AD29; Mon, 15 Feb 2021 12:24:45 +0000 (UTC) Date: Mon, 15 Feb 2021 13:24:45 +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: X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Mon 15-02-21 19:51:26, 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/ I do not see any real response to the pre-allocation argument except that put_page can be called from an atomic context. Which might be true in general but it is not the case for hugetlb pages. hugetlb_lock would have to be irq safe otherwise. Also the whole operation can be scheduled to a kworker context for a stronger allocation context. -- Michal Hocko SUSE Labs