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dkim=none (message not signed) header.d=none;amazon.com; dmarc=none action=none header.from=oracle.com; Received: from BY5PR10MB4196.namprd10.prod.outlook.com (2603:10b6:a03:20d::23) by BYAPR10MB2949.namprd10.prod.outlook.com (2603:10b6:a03:8f::27) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.20.3912.26; Wed, 10 Mar 2021 22:10:16 +0000 Received: from BY5PR10MB4196.namprd10.prod.outlook.com ([fe80::980e:61ba:57d2:47ee]) by BY5PR10MB4196.namprd10.prod.outlook.com ([fe80::980e:61ba:57d2:47ee%7]) with mapi id 15.20.3912.029; Wed, 10 Mar 2021 22:10:16 +0000 Subject: Re: [PATCH v18 4/9] mm: hugetlb: alloc the vmemmap pages associated with each HugeTLB page To: paulmck@kernel.org, Michal Hocko Cc: Muchun Song , corbet@lwn.net, 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, 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, osalvador@suse.de, song.bao.hua@hisilicon.com, david@redhat.com, naoya.horiguchi@nec.com, joao.m.martins@oracle.com, duanxiongchun@bytedance.com, linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, Chen Huang , Bodeddula Balasubramaniam References: <20210308102807.59745-1-songmuchun@bytedance.com> <20210308102807.59745-5-songmuchun@bytedance.com> <20210310214909.GY2696@paulmck-ThinkPad-P72> From: Mike Kravetz Message-ID: <68bc8cc9-a15b-2e97-9a2a-282fe6e9bd3f@oracle.com> Date: Wed, 10 Mar 2021 14:10:12 -0800 User-Agent: Mozilla/5.0 (X11; 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McKenney wrote: > On Wed, Mar 10, 2021 at 10:11:22PM +0100, Michal Hocko wrote: >> On Wed 10-03-21 10:56:08, Mike Kravetz wrote: >>> On 3/10/21 7:19 AM, Michal Hocko wrote: >>>> On Mon 08-03-21 18:28:02, Muchun Song wrote: >>>> [...] >>>>> @@ -1447,7 +1486,7 @@ void free_huge_page(struct page *page) >>>>> /* >>>>> * Defer freeing if in non-task context to avoid hugetlb_lock deadlock. >>>>> */ >>>>> - if (!in_task()) { >>>>> + if (in_atomic()) { >>>> >>>> As I've said elsewhere in_atomic doesn't work for CONFIG_PREEMPT_COUNT=n. >>>> We need this change for other reasons and so it would be better to pull >>>> it out into a separate patch which also makes HUGETLB depend on >>>> PREEMPT_COUNT. >>> >>> Yes, the issue of calling put_page for hugetlb pages from any context >>> still needs work. IMO, that is outside the scope of this series. We >>> already have code in this path which blocks/sleeps. >>> >>> Making HUGETLB depend on PREEMPT_COUNT is too restrictive. IIUC, >>> PREEMPT_COUNT will only be enabled if we enable: >>> PREEMPT "Preemptible Kernel (Low-Latency Desktop)" >>> PREEMPT_RT "Fully Preemptible Kernel (Real-Time)" >>> or, other 'debug' options. These are not enabled in 'more common' >>> kernels. Of course, we do not want to disable HUGETLB in common >>> configurations. >> >> I haven't tried that but PREEMPT_COUNT should be selectable even without >> any change to the preemption model (e.g. !PREEMPT). > > It works reliably for me, for example as in the diff below. So, > as Michal says, you should be able to add "select PREEMPT_COUNT" to > whatever Kconfig option you need to. > Thanks Paul. I may have been misreading Michal's suggestion of "make HUGETLB depend on PREEMPT_COUNT". We could "select PREEMPT_COUNT" if HUGETLB is enabled. However, since HUGETLB is enabled in most configs, then this would result in PREEMPT_COUNT also being enabled in most configs. I honestly do not know how much this will cost us? I assume that if it was free or really cheap it would already be always on? -- Mike Kravetz > Thanx, Paul > > diff --git a/kernel/rcu/Kconfig b/kernel/rcu/Kconfig > index 3128b7c..7d9f989 100644 > --- a/kernel/rcu/Kconfig > +++ b/kernel/rcu/Kconfig > @@ -8,6 +8,7 @@ menu "RCU Subsystem" > config TREE_RCU > bool > default y if SMP > + select PREEMPT_COUNT > help > This option selects the RCU implementation that is > designed for very large SMP system with hundreds or >