From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-qt0-f200.google.com (mail-qt0-f200.google.com [209.85.216.200]) by kanga.kvack.org (Postfix) with ESMTP id 627DB6B0691 for ; Fri, 17 Aug 2018 05:49:55 -0400 (EDT) Received: by mail-qt0-f200.google.com with SMTP id d25-v6so5828591qtp.10 for ; Fri, 17 Aug 2018 02:49:55 -0700 (PDT) Received: from mx1.redhat.com (mx3-rdu2.redhat.com. [66.187.233.73]) by mx.google.com with ESMTPS id 35-v6si612765qkz.103.2018.08.17.02.49.54 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Fri, 17 Aug 2018 02:49:54 -0700 (PDT) Subject: Re: [PATCH v4 3/4] mm/memory_hotplug: Define nodemask_t as a stack variable References: <20180817090017.17610-1-osalvador@techadventures.net> <20180817090017.17610-4-osalvador@techadventures.net> From: David Hildenbrand Message-ID: Date: Fri, 17 Aug 2018 11:49:51 +0200 MIME-Version: 1.0 In-Reply-To: <20180817090017.17610-4-osalvador@techadventures.net> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org List-ID: To: Oscar Salvador , akpm@linux-foundation.org Cc: mhocko@suse.com, vbabka@suse.cz, dan.j.williams@intel.com, yasu.isimatu@gmail.com, jonathan.cameron@huawei.com, Pavel.Tatashin@microsoft.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Oscar Salvador On 17.08.2018 11:00, Oscar Salvador wrote: > From: Oscar Salvador > > Currently, unregister_mem_sect_under_nodes() tries to allocate a nodemask_t > in order to check whithin the loop which nodes have already been unlinked, > so we do not repeat the operation on them. > > NODEMASK_ALLOC calls kmalloc() if NODES_SHIFT > 8, otherwise > it just declares a nodemask_t variable whithin the stack. > > Since kmalloc() can fail, we actually check whether NODEMASK_ALLOC failed > or not, and we return -ENOMEM accordingly. > remove_memory_section() does not check for the return value though. > It is pretty rare that such a tiny allocation can fail, but if it does, > we will be left with dangled symlinks under /sys/devices/system/node/, > since the mem_blk's directories will be removed no matter what > unregister_mem_sect_under_nodes() returns. > > One way to solve this is to check whether unlinked_nodes is NULL or not. > In the case it is not, we can just use it as before, but if it is NULL, > we can just skip the node_test_and_set check, and call sysfs_remove_link() > unconditionally. > This is harmless as sysfs_remove_link() backs off somewhere down the chain > in case the link has already been removed. > This method was presented in v3 of the path [1]. > > But since the maximum number of nodes we can have is 1024, > when NODES_SHIFT = 10, that gives us a nodemask_t of 128 bytes. > Although everything depends on how deep the stack is, I think we can afford > to define the nodemask_t variable whithin the stack. > > That simplifies the code, and we do not need to worry about untested error > code paths. > > If we see that this causes troubles with the stack, we can always return to [1]. > > [1] https://patchwork.kernel.org/patch/10566673/ > > Signed-off-by: Oscar Salvador > --- > drivers/base/node.c | 16 ++++++---------- > include/linux/node.h | 5 ++--- > 2 files changed, 8 insertions(+), 13 deletions(-) > > diff --git a/drivers/base/node.c b/drivers/base/node.c > index dd3bdab230b2..6b8c9b4537c9 100644 > --- a/drivers/base/node.c > +++ b/drivers/base/node.c > @@ -449,35 +449,31 @@ int register_mem_sect_under_node(struct memory_block *mem_blk, void *arg) > } > > /* unregister memory section under all nodes that it spans */ > -int unregister_mem_sect_under_nodes(struct memory_block *mem_blk, > +void unregister_mem_sect_under_nodes(struct memory_block *mem_blk, > unsigned long phys_index) I am a friend of fixing up alignment of other parameters. > { > - NODEMASK_ALLOC(nodemask_t, unlinked_nodes, GFP_KERNEL); > + nodemask_t unlinked_nodes; > unsigned long pfn, sect_start_pfn, sect_end_pfn; > > - if (!unlinked_nodes) > - return -ENOMEM; > - nodes_clear(*unlinked_nodes); > + nodes_clear(unlinked_nodes); > > sect_start_pfn = section_nr_to_pfn(phys_index); > sect_end_pfn = sect_start_pfn + PAGES_PER_SECTION - 1; > for (pfn = sect_start_pfn; pfn <= sect_end_pfn; pfn++) { > - int nid; > + int nid = get_nid_for_pfn(pfn); > > - nid = get_nid_for_pfn(pfn); > if (nid < 0) > continue; > if (!node_online(nid)) > continue; > - if (node_test_and_set(nid, *unlinked_nodes)) > + if (node_test_and_set(nid, unlinked_nodes)) > continue; > + > sysfs_remove_link(&node_devices[nid]->dev.kobj, > kobject_name(&mem_blk->dev.kobj)); > sysfs_remove_link(&mem_blk->dev.kobj, > kobject_name(&node_devices[nid]->dev.kobj)); > } > - NODEMASK_FREE(unlinked_nodes); > - return 0; > } > > int link_mem_sections(int nid, unsigned long start_pfn, unsigned long end_pfn) > diff --git a/include/linux/node.h b/include/linux/node.h > index 257bb3d6d014..1203378e596a 100644 > --- a/include/linux/node.h > +++ b/include/linux/node.h > @@ -72,7 +72,7 @@ extern int register_cpu_under_node(unsigned int cpu, unsigned int nid); > extern int unregister_cpu_under_node(unsigned int cpu, unsigned int nid); > extern int register_mem_sect_under_node(struct memory_block *mem_blk, > void *arg); > -extern int unregister_mem_sect_under_nodes(struct memory_block *mem_blk, > +extern void unregister_mem_sect_under_nodes(struct memory_block *mem_blk, > unsigned long phys_index); dito > > #ifdef CONFIG_HUGETLBFS > @@ -105,10 +105,9 @@ static inline int register_mem_sect_under_node(struct memory_block *mem_blk, > { > return 0; > } > -static inline int unregister_mem_sect_under_nodes(struct memory_block *mem_blk, > +static inline void unregister_mem_sect_under_nodes(struct memory_block *mem_blk, > unsigned long phys_index) dito > { > - return 0; > } > > static inline void register_hugetlbfs_with_node(node_registration_func_t reg, > We'll find out if we have enough stack :) But this is definitely simpler. -- Thanks, David / dhildenb