* [PATCH v2 0/3] Refactoring for remove_memory_section/unregister_mem_sect_under_nodes @ 2018-08-13 15:46 osalvador 2018-08-13 15:46 ` [PATCH v2 1/3] mm/memory-hotplug: Drop unused args from remove_memory_section osalvador ` (2 more replies) 0 siblings, 3 replies; 13+ messages in thread From: osalvador @ 2018-08-13 15:46 UTC (permalink / raw) To: akpm Cc: mhocko, dan.j.williams, jglisse, rafael, david, yasu.isimatu, logang, dave.jiang, Jonathan.Cameron, vbabka, linux-mm, linux-kernel, Oscar Salvador From: Oscar Salvador <osalvador@suse.de> This patchset does some cleanups and refactoring in the memory-hotplug code. The first and the second patch are pretty straightforward, as they only remove unused arguments/checks. The third one refactors unregister_mem_sect_under_nodes. This is needed to have a proper fallback in case we could not allocate memory. (details can be seen in patch3). Oscar Salvador (3): mm/memory-hotplug: Drop unused args from remove_memory_section mm/memory_hotplug: Drop mem_blk check from unregister_mem_sect_under_nodes mm/memory_hotplug: Refactor unregister_mem_sect_under_nodes drivers/base/memory.c | 5 ++--- drivers/base/node.c | 30 +++++++++++++++--------------- include/linux/node.h | 5 ++--- 3 files changed, 19 insertions(+), 21 deletions(-) -- 2.13.6 ^ permalink raw reply [flat|nested] 13+ messages in thread
* [PATCH v2 1/3] mm/memory-hotplug: Drop unused args from remove_memory_section 2018-08-13 15:46 [PATCH v2 0/3] Refactoring for remove_memory_section/unregister_mem_sect_under_nodes osalvador @ 2018-08-13 15:46 ` osalvador 2018-08-14 9:29 ` David Hildenbrand 2018-08-13 15:46 ` [PATCH v2 2/3] mm/memory_hotplug: Drop mem_blk check from unregister_mem_sect_under_nodes osalvador 2018-08-13 15:46 ` [PATCH v2 3/3] mm/memory_hotplug: Refactor unregister_mem_sect_under_nodes osalvador 2 siblings, 1 reply; 13+ messages in thread From: osalvador @ 2018-08-13 15:46 UTC (permalink / raw) To: akpm Cc: mhocko, dan.j.williams, jglisse, rafael, david, yasu.isimatu, logang, dave.jiang, Jonathan.Cameron, vbabka, linux-mm, linux-kernel, Oscar Salvador From: Oscar Salvador <osalvador@suse.de> unregister_memory_section() calls remove_memory_section() with three arguments: * node_id * section * phys_device Neither node_id nor phys_device are used. Let us drop them from the function. Signed-off-by: Oscar Salvador <osalvador@suse.de> --- drivers/base/memory.c | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-) diff --git a/drivers/base/memory.c b/drivers/base/memory.c index c8a1cb0b6136..2c622a9a7490 100644 --- a/drivers/base/memory.c +++ b/drivers/base/memory.c @@ -752,8 +752,7 @@ unregister_memory(struct memory_block *memory) device_unregister(&memory->dev); } -static int remove_memory_section(unsigned long node_id, - struct mem_section *section, int phys_device) +static int remove_memory_section(struct mem_section *section) { struct memory_block *mem; @@ -785,7 +784,7 @@ int unregister_memory_section(struct mem_section *section) if (!present_section(section)) return -EINVAL; - return remove_memory_section(0, section, 0); + return remove_memory_section(section); } #endif /* CONFIG_MEMORY_HOTREMOVE */ -- 2.13.6 ^ permalink raw reply related [flat|nested] 13+ messages in thread
* Re: [PATCH v2 1/3] mm/memory-hotplug: Drop unused args from remove_memory_section 2018-08-13 15:46 ` [PATCH v2 1/3] mm/memory-hotplug: Drop unused args from remove_memory_section osalvador @ 2018-08-14 9:29 ` David Hildenbrand 0 siblings, 0 replies; 13+ messages in thread From: David Hildenbrand @ 2018-08-14 9:29 UTC (permalink / raw) To: osalvador, akpm Cc: mhocko, dan.j.williams, jglisse, rafael, yasu.isimatu, logang, dave.jiang, Jonathan.Cameron, vbabka, linux-mm, linux-kernel, Oscar Salvador On 13.08.2018 17:46, osalvador@techadventures.net wrote: > From: Oscar Salvador <osalvador@suse.de> > > unregister_memory_section() calls remove_memory_section() > with three arguments: > > * node_id > * section > * phys_device > > Neither node_id nor phys_device are used. > Let us drop them from the function. > > Signed-off-by: Oscar Salvador <osalvador@suse.de> > --- > drivers/base/memory.c | 5 ++--- > 1 file changed, 2 insertions(+), 3 deletions(-) > > diff --git a/drivers/base/memory.c b/drivers/base/memory.c > index c8a1cb0b6136..2c622a9a7490 100644 > --- a/drivers/base/memory.c > +++ b/drivers/base/memory.c > @@ -752,8 +752,7 @@ unregister_memory(struct memory_block *memory) > device_unregister(&memory->dev); > } > > -static int remove_memory_section(unsigned long node_id, > - struct mem_section *section, int phys_device) > +static int remove_memory_section(struct mem_section *section) > { > struct memory_block *mem; > > @@ -785,7 +784,7 @@ int unregister_memory_section(struct mem_section *section) > if (!present_section(section)) > return -EINVAL; > > - return remove_memory_section(0, section, 0); > + return remove_memory_section(section); > } > #endif /* CONFIG_MEMORY_HOTREMOVE */ > > Reviewed-by: David Hildenbrand <david@redhat.com> -- Thanks, David / dhildenb ^ permalink raw reply [flat|nested] 13+ messages in thread
* [PATCH v2 2/3] mm/memory_hotplug: Drop mem_blk check from unregister_mem_sect_under_nodes 2018-08-13 15:46 [PATCH v2 0/3] Refactoring for remove_memory_section/unregister_mem_sect_under_nodes osalvador 2018-08-13 15:46 ` [PATCH v2 1/3] mm/memory-hotplug: Drop unused args from remove_memory_section osalvador @ 2018-08-13 15:46 ` osalvador 2018-08-14 9:30 ` David Hildenbrand 2018-08-13 15:46 ` [PATCH v2 3/3] mm/memory_hotplug: Refactor unregister_mem_sect_under_nodes osalvador 2 siblings, 1 reply; 13+ messages in thread From: osalvador @ 2018-08-13 15:46 UTC (permalink / raw) To: akpm Cc: mhocko, dan.j.williams, jglisse, rafael, david, yasu.isimatu, logang, dave.jiang, Jonathan.Cameron, vbabka, linux-mm, linux-kernel, Oscar Salvador From: Oscar Salvador <osalvador@suse.de> Before calling to unregister_mem_sect_under_nodes(), remove_memory_section() already checks if we got a valid memory_block. No need to check that again in unregister_mem_sect_under_nodes(). Signed-off-by: Oscar Salvador <osalvador@suse.de> --- drivers/base/node.c | 4 ---- 1 file changed, 4 deletions(-) diff --git a/drivers/base/node.c b/drivers/base/node.c index 1ac4c36e13bb..dd3bdab230b2 100644 --- a/drivers/base/node.c +++ b/drivers/base/node.c @@ -455,10 +455,6 @@ int unregister_mem_sect_under_nodes(struct memory_block *mem_blk, NODEMASK_ALLOC(nodemask_t, unlinked_nodes, GFP_KERNEL); unsigned long pfn, sect_start_pfn, sect_end_pfn; - if (!mem_blk) { - NODEMASK_FREE(unlinked_nodes); - return -EFAULT; - } if (!unlinked_nodes) return -ENOMEM; nodes_clear(*unlinked_nodes); -- 2.13.6 ^ permalink raw reply related [flat|nested] 13+ messages in thread
* Re: [PATCH v2 2/3] mm/memory_hotplug: Drop mem_blk check from unregister_mem_sect_under_nodes 2018-08-13 15:46 ` [PATCH v2 2/3] mm/memory_hotplug: Drop mem_blk check from unregister_mem_sect_under_nodes osalvador @ 2018-08-14 9:30 ` David Hildenbrand 2018-08-14 9:36 ` Oscar Salvador 0 siblings, 1 reply; 13+ messages in thread From: David Hildenbrand @ 2018-08-14 9:30 UTC (permalink / raw) To: osalvador, akpm Cc: mhocko, dan.j.williams, jglisse, rafael, yasu.isimatu, logang, dave.jiang, Jonathan.Cameron, vbabka, linux-mm, linux-kernel, Oscar Salvador On 13.08.2018 17:46, osalvador@techadventures.net wrote: > From: Oscar Salvador <osalvador@suse.de> > > Before calling to unregister_mem_sect_under_nodes(), > remove_memory_section() already checks if we got a valid > memory_block. > > No need to check that again in unregister_mem_sect_under_nodes(). > > Signed-off-by: Oscar Salvador <osalvador@suse.de> > --- > drivers/base/node.c | 4 ---- > 1 file changed, 4 deletions(-) > > diff --git a/drivers/base/node.c b/drivers/base/node.c > index 1ac4c36e13bb..dd3bdab230b2 100644 > --- a/drivers/base/node.c > +++ b/drivers/base/node.c > @@ -455,10 +455,6 @@ int unregister_mem_sect_under_nodes(struct memory_block *mem_blk, > NODEMASK_ALLOC(nodemask_t, unlinked_nodes, GFP_KERNEL); > unsigned long pfn, sect_start_pfn, sect_end_pfn; > > - if (!mem_blk) { > - NODEMASK_FREE(unlinked_nodes); > - return -EFAULT; > - } > if (!unlinked_nodes) > return -ENOMEM; > nodes_clear(*unlinked_nodes); > While it is correct in current code, I wonder if this sanity check should stay. I would completely agree if it would be a static function. -- Thanks, David / dhildenb ^ permalink raw reply [flat|nested] 13+ messages in thread
* Re: [PATCH v2 2/3] mm/memory_hotplug: Drop mem_blk check from unregister_mem_sect_under_nodes 2018-08-14 9:30 ` David Hildenbrand @ 2018-08-14 9:36 ` Oscar Salvador 2018-08-14 9:44 ` David Hildenbrand 0 siblings, 1 reply; 13+ messages in thread From: Oscar Salvador @ 2018-08-14 9:36 UTC (permalink / raw) To: David Hildenbrand Cc: akpm, mhocko, dan.j.williams, jglisse, rafael, yasu.isimatu, logang, dave.jiang, Jonathan.Cameron, vbabka, linux-mm, linux-kernel, Oscar Salvador On Tue, Aug 14, 2018 at 11:30:51AM +0200, David Hildenbrand wrote: > > While it is correct in current code, I wonder if this sanity check > should stay. I would completely agree if it would be a static function. Hi David, Well, unregister_mem_sect_under_nodes() __only__ gets called from remove_memory_section(). But remove_memory_section() only calls unregister_mem_sect_under_nodes() IFF mem_blk is not NULL: static int remove_memory_section { ... mem = find_memory_block(section); if (!mem) goto out_unlock; unregister_mem_sect_under_nodes(mem, __section_nr(section)); ... } So, to me keeping the check is redundant, as we already check for it before calling in. Thanks -- Oscar Salvador SUSE L3 ^ permalink raw reply [flat|nested] 13+ messages in thread
* Re: [PATCH v2 2/3] mm/memory_hotplug: Drop mem_blk check from unregister_mem_sect_under_nodes 2018-08-14 9:36 ` Oscar Salvador @ 2018-08-14 9:44 ` David Hildenbrand 2018-08-14 10:06 ` Oscar Salvador 0 siblings, 1 reply; 13+ messages in thread From: David Hildenbrand @ 2018-08-14 9:44 UTC (permalink / raw) To: Oscar Salvador Cc: akpm, mhocko, dan.j.williams, jglisse, rafael, yasu.isimatu, logang, dave.jiang, Jonathan.Cameron, vbabka, linux-mm, linux-kernel, Oscar Salvador On 14.08.2018 11:36, Oscar Salvador wrote: > On Tue, Aug 14, 2018 at 11:30:51AM +0200, David Hildenbrand wrote: > >> >> While it is correct in current code, I wonder if this sanity check >> should stay. I would completely agree if it would be a static function. > > Hi David, > > Well, unregister_mem_sect_under_nodes() __only__ gets called from remove_memory_section(). > But remove_memory_section() only calls unregister_mem_sect_under_nodes() IFF mem_blk > is not NULL: > > static int remove_memory_section > { > ... > mem = find_memory_block(section); > if (!mem) > goto out_unlock; > > unregister_mem_sect_under_nodes(mem, __section_nr(section)); > ... > } Yes I know, as I said, if it would be local to a file I would not care. Making this functions never return an error is nice, though (and as you noted, the return value is never checked). I am a friend of stating which conditions a function expects to hold if a function can be called from other parts of the system. Usually I prefer to use BUG_ONs for that (whoever decides to call it can directly see what he as to check before calling) or comments. But comments tend to become obsolete. > > So, to me keeping the check is redundant, as we already check for it before calling in. > > Thanks > -- Thanks, David / dhildenb ^ permalink raw reply [flat|nested] 13+ messages in thread
* Re: [PATCH v2 2/3] mm/memory_hotplug: Drop mem_blk check from unregister_mem_sect_under_nodes 2018-08-14 9:44 ` David Hildenbrand @ 2018-08-14 10:06 ` Oscar Salvador 2018-08-14 10:09 ` David Hildenbrand 0 siblings, 1 reply; 13+ messages in thread From: Oscar Salvador @ 2018-08-14 10:06 UTC (permalink / raw) To: David Hildenbrand Cc: akpm, mhocko, dan.j.williams, jglisse, rafael, yasu.isimatu, logang, dave.jiang, Jonathan.Cameron, vbabka, linux-mm, linux-kernel, Oscar Salvador On Tue, Aug 14, 2018 at 11:44:50AM +0200, David Hildenbrand wrote: > > Yes I know, as I said, if it would be local to a file I would not care. > Making this functions never return an error is nice, though (and as you > noted, the return value is never checked). > > I am a friend of stating which conditions a function expects to hold if > a function can be called from other parts of the system. Usually I > prefer to use BUG_ONs for that (whoever decides to call it can directly > see what he as to check before calling) or comments. But comments tend > to become obsolete. Uhm, I think a BUG_ON is too much here. We could replace the check with a WARN_ON, just in case a new function decides to call unregister_mem_sect_under_nodes() in the future. Something like: WARN_ON(!mem_blk) return; In that case, we should get a nice splat in the logs that should tell us who is calling it with an invalid mem_blk. -- Oscar Salvador SUSE L3 ^ permalink raw reply [flat|nested] 13+ messages in thread
* Re: [PATCH v2 2/3] mm/memory_hotplug: Drop mem_blk check from unregister_mem_sect_under_nodes 2018-08-14 10:06 ` Oscar Salvador @ 2018-08-14 10:09 ` David Hildenbrand 2018-08-14 12:36 ` Oscar Salvador 0 siblings, 1 reply; 13+ messages in thread From: David Hildenbrand @ 2018-08-14 10:09 UTC (permalink / raw) To: Oscar Salvador Cc: akpm, mhocko, dan.j.williams, jglisse, rafael, yasu.isimatu, logang, dave.jiang, Jonathan.Cameron, vbabka, linux-mm, linux-kernel, Oscar Salvador On 14.08.2018 12:06, Oscar Salvador wrote: > On Tue, Aug 14, 2018 at 11:44:50AM +0200, David Hildenbrand wrote: >> >> Yes I know, as I said, if it would be local to a file I would not care. >> Making this functions never return an error is nice, though (and as you >> noted, the return value is never checked). >> >> I am a friend of stating which conditions a function expects to hold if >> a function can be called from other parts of the system. Usually I >> prefer to use BUG_ONs for that (whoever decides to call it can directly >> see what he as to check before calling) or comments. But comments tend >> to become obsolete. > > Uhm, I think a BUG_ON is too much here. > We could replace the check with a WARN_ON, just in case > a new function decides to call unregister_mem_sect_under_nodes() in the future. > > Something like: > > WARN_ON(!mem_blk) > return; > > In that case, we should get a nice splat in the logs that should tell us > who is calling it with an invalid mem_blk. > Whatever you think is best. I have no idea what the general rules in MM code are. Maybe dropping this check is totally fine. -- Thanks, David / dhildenb ^ permalink raw reply [flat|nested] 13+ messages in thread
* Re: [PATCH v2 2/3] mm/memory_hotplug: Drop mem_blk check from unregister_mem_sect_under_nodes 2018-08-14 10:09 ` David Hildenbrand @ 2018-08-14 12:36 ` Oscar Salvador 0 siblings, 0 replies; 13+ messages in thread From: Oscar Salvador @ 2018-08-14 12:36 UTC (permalink / raw) To: David Hildenbrand Cc: akpm, mhocko, dan.j.williams, jglisse, rafael, yasu.isimatu, logang, dave.jiang, Jonathan.Cameron, vbabka, linux-mm, linux-kernel, Oscar Salvador On Tue, Aug 14, 2018 at 12:09:14PM +0200, David Hildenbrand wrote: > > Whatever you think is best. I have no idea what the general rules in MM > code are. Maybe dropping this check is totally fine. Well, if you ask me, callers should care for validating mem_blk before calling in. But a WARN_ON is not harmful either. Let us just wait to hear more from others. Thanks -- Oscar Salvador SUSE L3 ^ permalink raw reply [flat|nested] 13+ messages in thread
* [PATCH v2 3/3] mm/memory_hotplug: Refactor unregister_mem_sect_under_nodes 2018-08-13 15:46 [PATCH v2 0/3] Refactoring for remove_memory_section/unregister_mem_sect_under_nodes osalvador 2018-08-13 15:46 ` [PATCH v2 1/3] mm/memory-hotplug: Drop unused args from remove_memory_section osalvador 2018-08-13 15:46 ` [PATCH v2 2/3] mm/memory_hotplug: Drop mem_blk check from unregister_mem_sect_under_nodes osalvador @ 2018-08-13 15:46 ` osalvador 2018-08-14 9:39 ` David Hildenbrand 2 siblings, 1 reply; 13+ messages in thread From: osalvador @ 2018-08-13 15:46 UTC (permalink / raw) To: akpm Cc: mhocko, dan.j.williams, jglisse, rafael, david, yasu.isimatu, logang, dave.jiang, Jonathan.Cameron, vbabka, linux-mm, linux-kernel, Oscar Salvador From: Oscar Salvador <osalvador@suse.de> 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 kamlloc() 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. The problem with this is that if we return -ENOMEM, it means that unregister_mem_sect_under_nodes will not be able to remove the symlinks, but since we do not check the return value, we go ahead and we call unregister_memory(), which will remove all the mem_blks directories. This will leave us with dangled symlinks. The easiest way to overcome this is to fallback by calling sysfs_remove_link() unconditionally in case NODEMASK_ALLOC failed. This means that we will call sysfs_remove_link on nodes that have been already unlinked, but nothing wrong happens as sysfs_remove_link() backs off somewhere down the chain in case the link has already been removed. I think that this is better than a) dangled symlinks b) having to recovery from such error in remove_memory_section Since from now on we will not need to take care about return values, we can make the function void. While at it, we can also drop the node_online() check, as a node can only be offline if all the memory/cpus associated with it have been removed. As we have a safe fallback, one thing that could also be done is to add __GFP_NORETRY in the flags when calling NODEMASK_ALLOC, so we do not retry. Signed-off-by: Oscar Salvador <osalvador@suse.de> --- drivers/base/node.c | 26 +++++++++++++++----------- include/linux/node.h | 5 ++--- 2 files changed, 17 insertions(+), 14 deletions(-) diff --git a/drivers/base/node.c b/drivers/base/node.c index dd3bdab230b2..0a3ca62687ea 100644 --- a/drivers/base/node.c +++ b/drivers/base/node.c @@ -449,35 +449,39 @@ 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) { NODEMASK_ALLOC(nodemask_t, unlinked_nodes, GFP_KERNEL); unsigned long pfn, sect_start_pfn, sect_end_pfn; - if (!unlinked_nodes) - return -ENOMEM; - nodes_clear(*unlinked_nodes); + if (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)) + /* + * It is possible that NODEMASK_ALLOC fails due to memory pressure. + * If that happens, we fallback to call sysfs_remove_link unconditionally. + * Nothing wrong will happen as sysfs_remove_link will back off + * somewhere down the chain in case the link has already been removed. + */ + if (unlinked_nodes && 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; + + if (unlinked_nodes) + NODEMASK_FREE(unlinked_nodes); } 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); #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) { - return 0; } static inline void register_hugetlbfs_with_node(node_registration_func_t reg, -- 2.13.6 ^ permalink raw reply related [flat|nested] 13+ messages in thread
* Re: [PATCH v2 3/3] mm/memory_hotplug: Refactor unregister_mem_sect_under_nodes 2018-08-13 15:46 ` [PATCH v2 3/3] mm/memory_hotplug: Refactor unregister_mem_sect_under_nodes osalvador @ 2018-08-14 9:39 ` David Hildenbrand 2018-08-14 9:55 ` Oscar Salvador 0 siblings, 1 reply; 13+ messages in thread From: David Hildenbrand @ 2018-08-14 9:39 UTC (permalink / raw) To: osalvador, akpm Cc: mhocko, dan.j.williams, jglisse, rafael, yasu.isimatu, logang, dave.jiang, Jonathan.Cameron, vbabka, linux-mm, linux-kernel, Oscar Salvador On 13.08.2018 17:46, osalvador@techadventures.net wrote: > From: Oscar Salvador <osalvador@suse.de> > > 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 kamlloc() 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. > > The problem with this is that if we return -ENOMEM, it means that > unregister_mem_sect_under_nodes will not be able to remove the symlinks, > but since we do not check the return value, we go ahead and we call unregister_memory(), > which will remove all the mem_blks directories. > > This will leave us with dangled symlinks. > > The easiest way to overcome this is to fallback by calling sysfs_remove_link() > unconditionally in case NODEMASK_ALLOC failed. > This means that we will call sysfs_remove_link on nodes that have been already unlinked, > but nothing wrong happens as sysfs_remove_link() backs off somewhere down the chain in case > the link has already been removed. > > I think that this is better than > > a) dangled symlinks > b) having to recovery from such error in remove_memory_section > > Since from now on we will not need to take care about return values, we can make the function void. > > While at it, we can also drop the node_online() check, as a node can only be > offline if all the memory/cpus associated with it have been removed. I would prefer splitting this change out into a separate patch. > > As we have a safe fallback, one thing that could also be done is to add __GFP_NORETRY > in the flags when calling NODEMASK_ALLOC, so we do not retry. > > Signed-off-by: Oscar Salvador <osalvador@suse.de> > --- > drivers/base/node.c | 26 +++++++++++++++----------- > include/linux/node.h | 5 ++--- > 2 files changed, 17 insertions(+), 14 deletions(-) > > diff --git a/drivers/base/node.c b/drivers/base/node.c > index dd3bdab230b2..0a3ca62687ea 100644 > --- a/drivers/base/node.c > +++ b/drivers/base/node.c > @@ -449,35 +449,39 @@ 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) > { > NODEMASK_ALLOC(nodemask_t, unlinked_nodes, GFP_KERNEL); > unsigned long pfn, sect_start_pfn, sect_end_pfn; > > - if (!unlinked_nodes) > - return -ENOMEM; > - nodes_clear(*unlinked_nodes); > + if (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)) > + /* > + * It is possible that NODEMASK_ALLOC fails due to memory pressure. > + * If that happens, we fallback to call sysfs_remove_link unconditionally. > + * Nothing wrong will happen as sysfs_remove_link will back off > + * somewhere down the chain in case the link has already been removed. > + */ > + if (unlinked_nodes && 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; > + > + if (unlinked_nodes) > + NODEMASK_FREE(unlinked_nodes); NODEMASK_FEEE/kfree can deal with NULL pointers. > } > > 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); > > #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) > { > - return 0; > } > > static inline void register_hugetlbfs_with_node(node_registration_func_t reg, > -- Thanks, David / dhildenb ^ permalink raw reply [flat|nested] 13+ messages in thread
* Re: [PATCH v2 3/3] mm/memory_hotplug: Refactor unregister_mem_sect_under_nodes 2018-08-14 9:39 ` David Hildenbrand @ 2018-08-14 9:55 ` Oscar Salvador 0 siblings, 0 replies; 13+ messages in thread From: Oscar Salvador @ 2018-08-14 9:55 UTC (permalink / raw) To: David Hildenbrand Cc: akpm, mhocko, dan.j.williams, jglisse, rafael, yasu.isimatu, logang, dave.jiang, Jonathan.Cameron, vbabka, linux-mm, linux-kernel, Oscar Salvador On Tue, Aug 14, 2018 at 11:39:34AM +0200, David Hildenbrand wrote: > On 13.08.2018 17:46, osalvador@techadventures.net wrote: > > From: Oscar Salvador <osalvador@suse.de> > > While at it, we can also drop the node_online() check, as a node can only be > > offline if all the memory/cpus associated with it have been removed. > > I would prefer splitting this change out into a separate patch. Yes, I guess it is better as it is not really related to the changes in this patch. I will wait for more feedback and I will split it up in v3. > > + > > + if (unlinked_nodes) > > + NODEMASK_FREE(unlinked_nodes); > > NODEMASK_FEEE/kfree can deal with NULL pointers. Good point, I missed that. I will fix it up in v3. Thanks for reviewing. -- Oscar Salvador SUSE L3 ^ permalink raw reply [flat|nested] 13+ messages in thread
end of thread, other threads:[~2018-08-14 12:36 UTC | newest] Thread overview: 13+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2018-08-13 15:46 [PATCH v2 0/3] Refactoring for remove_memory_section/unregister_mem_sect_under_nodes osalvador 2018-08-13 15:46 ` [PATCH v2 1/3] mm/memory-hotplug: Drop unused args from remove_memory_section osalvador 2018-08-14 9:29 ` David Hildenbrand 2018-08-13 15:46 ` [PATCH v2 2/3] mm/memory_hotplug: Drop mem_blk check from unregister_mem_sect_under_nodes osalvador 2018-08-14 9:30 ` David Hildenbrand 2018-08-14 9:36 ` Oscar Salvador 2018-08-14 9:44 ` David Hildenbrand 2018-08-14 10:06 ` Oscar Salvador 2018-08-14 10:09 ` David Hildenbrand 2018-08-14 12:36 ` Oscar Salvador 2018-08-13 15:46 ` [PATCH v2 3/3] mm/memory_hotplug: Refactor unregister_mem_sect_under_nodes osalvador 2018-08-14 9:39 ` David Hildenbrand 2018-08-14 9:55 ` Oscar Salvador
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