| Message ID | 20181130065847.13714-1-richard.weiyang@gmail.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [v3] mm, hotplug: move init_currently_empty_zone() under zone_span_lock protection | expand |
On 30.11.18 07:58, Wei Yang wrote: > During online_pages phase, pgdat->nr_zones will be updated in case this > zone is empty. > > Currently the online_pages phase is protected by the global lock > mem_hotplug_begin(), which ensures there is no contention during the > update of nr_zones. But this global lock introduces scalability issues. > > The patch moves init_currently_empty_zone under both zone_span_writelock > and pgdat_resize_lock because both the pgdat state is changed (nr_zones) > and the zone's start_pfn. Also this patch changes the documentation > of node_size_lock to include the protectioin of nr_zones. s/protectioin/protection/ > > Signed-off-by: Wei Yang <richard.weiyang@gmail.com> > Acked-by: Michal Hocko <mhocko@suse.com> > Reviewed-by: Oscar Salvador <osalvador@suse.de> > CC: David Hildenbrand <david@redhat.com> > > --- > David, I may not catch you exact comment on the code or changelog. If I > missed, just let me know. I guess I would have rewritten it to something like the following " Currently the online_pages phase is protected by two global locks (device_device_hotplug_lock and mem_hotplug_lock). Especial the latter can result in scalability issues, as it will slow down code relying on get_online_mems(). Let's prepare code for not having to rely on get_online_mems() but instead some more fine grained locks. During online_pages phase, pgdat->nr_zones will be updated in case the zone is empty. Right now mem_hotplug_lock ensures that there is no contention during the update of nr_zones. The patch moves init_currently_empty_zone under both zone_span_writelock and pgdat_resize_lock because both the pgdat state is changed (nr_zones) and the zone's start_pfn. Also this patch changes the documentation of node_size_lock to include the protection of nr_zones. " Does that make sense? > > --- > v3: > * slightly modify the last paragraph of changelog based on Michal's > comment > v2: > * commit log changes > * modify the code in move_pfn_range_to_zone() instead of in > init_currently_empty_zone() > * pgdat_resize_lock documentation change > --- > include/linux/mmzone.h | 7 ++++--- > mm/memory_hotplug.c | 5 ++--- > 2 files changed, 6 insertions(+), 6 deletions(-) > > diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h > index 3d0c472438d2..37d9c5c3faa6 100644 > --- a/include/linux/mmzone.h > +++ b/include/linux/mmzone.h > @@ -635,9 +635,10 @@ typedef struct pglist_data { > #endif > #if defined(CONFIG_MEMORY_HOTPLUG) || defined(CONFIG_DEFERRED_STRUCT_PAGE_INIT) > /* > - * Must be held any time you expect node_start_pfn, node_present_pages > - * or node_spanned_pages stay constant. Holding this will also > - * guarantee that any pfn_valid() stays that way. > + * Must be held any time you expect node_start_pfn, > + * node_present_pages, node_spanned_pages or nr_zones stay constant. > + * Holding this will also guarantee that any pfn_valid() stays that > + * way. > * > * pgdat_resize_lock() and pgdat_resize_unlock() are provided to > * manipulate node_size_lock without checking for CONFIG_MEMORY_HOTPLUG > diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c > index 61972da38d93..f626e7e5f57b 100644 > --- a/mm/memory_hotplug.c > +++ b/mm/memory_hotplug.c > @@ -742,14 +742,13 @@ void __ref move_pfn_range_to_zone(struct zone *zone, unsigned long start_pfn, > int nid = pgdat->node_id; > unsigned long flags; > > - if (zone_is_empty(zone)) > - init_currently_empty_zone(zone, start_pfn, nr_pages); > - > clear_zone_contiguous(zone); > > /* TODO Huh pgdat is irqsave while zone is not. It used to be like that before */ > pgdat_resize_lock(pgdat, &flags); > zone_span_writelock(zone); > + if (zone_is_empty(zone)) > + init_currently_empty_zone(zone, start_pfn, nr_pages); > resize_zone_range(zone, start_pfn, nr_pages); > zone_span_writeunlock(zone); > resize_pgdat_range(pgdat, start_pfn, nr_pages); >
On Fri, Nov 30, 2018 at 10:30:22AM +0100, David Hildenbrand wrote: >On 30.11.18 07:58, Wei Yang wrote: >> During online_pages phase, pgdat->nr_zones will be updated in case this >> zone is empty. >> >> Currently the online_pages phase is protected by the global lock >> mem_hotplug_begin(), which ensures there is no contention during the >> update of nr_zones. But this global lock introduces scalability issues. >> >> The patch moves init_currently_empty_zone under both zone_span_writelock >> and pgdat_resize_lock because both the pgdat state is changed (nr_zones) >> and the zone's start_pfn. Also this patch changes the documentation >> of node_size_lock to include the protectioin of nr_zones. > >s/protectioin/protection/ > >> >> Signed-off-by: Wei Yang <richard.weiyang@gmail.com> >> Acked-by: Michal Hocko <mhocko@suse.com> >> Reviewed-by: Oscar Salvador <osalvador@suse.de> >> CC: David Hildenbrand <david@redhat.com> >> >> --- >> David, I may not catch you exact comment on the code or changelog. If I >> missed, just let me know. > >I guess I would have rewritten it to something like the following > >" >Currently the online_pages phase is protected by two global locks >(device_device_hotplug_lock and mem_hotplug_lock). Especial the latter >can result in scalability issues, as it will slow down code relying on >get_online_mems(). Let's prepare code for not having to rely on >get_online_mems() but instead some more fine grained locks. I am not sure why we specify get_online_mems() here. mem_hotplug_lock is grabed in many places besides this one. In my mind, each place introduce scalability issue, not only this one. Or you want to say, the mem_hotplug_lock will introduce scalability issue in two place: * hotplug process itself * slab allocation process The second one is more critical. And this is what we try to address? > >During online_pages phase, pgdat->nr_zones will be updated in case the >zone is empty. Right now mem_hotplug_lock ensures that there is no >contention during the update of nr_zones. > >The patch moves init_currently_empty_zone under both zone_span_writelock >and pgdat_resize_lock because both the pgdat state is changed (nr_zones) >and the zone's start_pfn. Also this patch changes the documentation >of node_size_lock to include the protection of nr_zones. >" > >Does that make sense? > >> >> --- >> v3: >> * slightly modify the last paragraph of changelog based on Michal's >> comment >> v2: >> * commit log changes >> * modify the code in move_pfn_range_to_zone() instead of in >> init_currently_empty_zone() >> * pgdat_resize_lock documentation change >> --- >> include/linux/mmzone.h | 7 ++++--- >> mm/memory_hotplug.c | 5 ++--- >> 2 files changed, 6 insertions(+), 6 deletions(-) >> >> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h >> index 3d0c472438d2..37d9c5c3faa6 100644 >> --- a/include/linux/mmzone.h >> +++ b/include/linux/mmzone.h >> @@ -635,9 +635,10 @@ typedef struct pglist_data { >> #endif >> #if defined(CONFIG_MEMORY_HOTPLUG) || defined(CONFIG_DEFERRED_STRUCT_PAGE_INIT) >> /* >> - * Must be held any time you expect node_start_pfn, node_present_pages >> - * or node_spanned_pages stay constant. Holding this will also >> - * guarantee that any pfn_valid() stays that way. >> + * Must be held any time you expect node_start_pfn, >> + * node_present_pages, node_spanned_pages or nr_zones stay constant. >> + * Holding this will also guarantee that any pfn_valid() stays that >> + * way. >> * >> * pgdat_resize_lock() and pgdat_resize_unlock() are provided to >> * manipulate node_size_lock without checking for CONFIG_MEMORY_HOTPLUG >> diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c >> index 61972da38d93..f626e7e5f57b 100644 >> --- a/mm/memory_hotplug.c >> +++ b/mm/memory_hotplug.c >> @@ -742,14 +742,13 @@ void __ref move_pfn_range_to_zone(struct zone *zone, unsigned long start_pfn, >> int nid = pgdat->node_id; >> unsigned long flags; >> >> - if (zone_is_empty(zone)) >> - init_currently_empty_zone(zone, start_pfn, nr_pages); >> - >> clear_zone_contiguous(zone); >> >> /* TODO Huh pgdat is irqsave while zone is not. It used to be like that before */ >> pgdat_resize_lock(pgdat, &flags); >> zone_span_writelock(zone); >> + if (zone_is_empty(zone)) >> + init_currently_empty_zone(zone, start_pfn, nr_pages); >> resize_zone_range(zone, start_pfn, nr_pages); >> zone_span_writeunlock(zone); >> resize_pgdat_range(pgdat, start_pfn, nr_pages); >> > > >-- > >Thanks, > >David / dhildenb
On 01.12.18 01:27, Wei Yang wrote: > On Fri, Nov 30, 2018 at 10:30:22AM +0100, David Hildenbrand wrote: >> On 30.11.18 07:58, Wei Yang wrote: >>> During online_pages phase, pgdat->nr_zones will be updated in case this >>> zone is empty. >>> >>> Currently the online_pages phase is protected by the global lock >>> mem_hotplug_begin(), which ensures there is no contention during the >>> update of nr_zones. But this global lock introduces scalability issues. >>> >>> The patch moves init_currently_empty_zone under both zone_span_writelock >>> and pgdat_resize_lock because both the pgdat state is changed (nr_zones) >>> and the zone's start_pfn. Also this patch changes the documentation >>> of node_size_lock to include the protectioin of nr_zones. >> >> s/protectioin/protection/ >> >>> >>> Signed-off-by: Wei Yang <richard.weiyang@gmail.com> >>> Acked-by: Michal Hocko <mhocko@suse.com> >>> Reviewed-by: Oscar Salvador <osalvador@suse.de> >>> CC: David Hildenbrand <david@redhat.com> >>> >>> --- >>> David, I may not catch you exact comment on the code or changelog. If I >>> missed, just let me know. >> >> I guess I would have rewritten it to something like the following >> >> " >> Currently the online_pages phase is protected by two global locks >> (device_device_hotplug_lock and mem_hotplug_lock). Especial the latter >> can result in scalability issues, as it will slow down code relying on >> get_online_mems(). Let's prepare code for not having to rely on >> get_online_mems() but instead some more fine grained locks. > > I am not sure why we specify get_online_mems() here. mem_hotplug_lock is > grabed in many places besides this one. In my mind, each place introduce > scalability issue, not only this one. mem_hotplug_lock is grabbed in write only when adding/removing/onlining/offlining memory and when adding/removing device memory. The read locker are the critical part for now. > > Or you want to say, the mem_hotplug_lock will introduce scalability > issue in two place: > > * hotplug process itself > * slab allocation process > > The second one is more critical. And this is what we try to address? Indeed, especially as the first usually (except device memory) also uses the device_hotplug_lock, I only consider the second one critical. Feel free to change this description to whatever you like. As I already stated scalability of adding/removing/onlining/offlining is not really an issue as of now (prove me wrong :) ). So I would not care about including such information in this patch.
On Mon, Dec 03, 2018 at 11:09:52AM +0100, David Hildenbrand wrote: >On 01.12.18 01:27, Wei Yang wrote: >> On Fri, Nov 30, 2018 at 10:30:22AM +0100, David Hildenbrand wrote: >>> On 30.11.18 07:58, Wei Yang wrote: >>>> During online_pages phase, pgdat->nr_zones will be updated in case this >>>> zone is empty. >>>> >>>> Currently the online_pages phase is protected by the global lock >>>> mem_hotplug_begin(), which ensures there is no contention during the >>>> update of nr_zones. But this global lock introduces scalability issues. >>>> >>>> The patch moves init_currently_empty_zone under both zone_span_writelock >>>> and pgdat_resize_lock because both the pgdat state is changed (nr_zones) >>>> and the zone's start_pfn. Also this patch changes the documentation >>>> of node_size_lock to include the protectioin of nr_zones. >>> >>> s/protectioin/protection/ >>> >>>> >>>> Signed-off-by: Wei Yang <richard.weiyang@gmail.com> >>>> Acked-by: Michal Hocko <mhocko@suse.com> >>>> Reviewed-by: Oscar Salvador <osalvador@suse.de> >>>> CC: David Hildenbrand <david@redhat.com> >>>> >>>> --- >>>> David, I may not catch you exact comment on the code or changelog. If I >>>> missed, just let me know. >>> >>> I guess I would have rewritten it to something like the following >>> >>> " >>> Currently the online_pages phase is protected by two global locks >>> (device_device_hotplug_lock and mem_hotplug_lock). Especial the latter >>> can result in scalability issues, as it will slow down code relying on >>> get_online_mems(). Let's prepare code for not having to rely on >>> get_online_mems() but instead some more fine grained locks. >> >> I am not sure why we specify get_online_mems() here. mem_hotplug_lock is >> grabed in many places besides this one. In my mind, each place introduce >> scalability issue, not only this one. > >mem_hotplug_lock is grabbed in write only when >adding/removing/onlining/offlining memory and when adding/removing >device memory. The read locker are the critical part for now. > >> >> Or you want to say, the mem_hotplug_lock will introduce scalability >> issue in two place: >> >> * hotplug process itself >> * slab allocation process >> >> The second one is more critical. And this is what we try to address? > >Indeed, especially as the first usually (except device memory) also uses >the device_hotplug_lock, I only consider the second one critical. > >Feel free to change this description to whatever you like. >As I already stated scalability of adding/removing/onlining/offlining is >not really an issue as of now (prove me wrong :) ). So I would not care >about including such information in this patch. > Thanks for your information. Let me try to reword the changelog. >-- > >Thanks, > >David / dhildenb
diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h index 3d0c472438d2..37d9c5c3faa6 100644 --- a/include/linux/mmzone.h +++ b/include/linux/mmzone.h @@ -635,9 +635,10 @@ typedef struct pglist_data { #endif #if defined(CONFIG_MEMORY_HOTPLUG) || defined(CONFIG_DEFERRED_STRUCT_PAGE_INIT) /* - * Must be held any time you expect node_start_pfn, node_present_pages - * or node_spanned_pages stay constant. Holding this will also - * guarantee that any pfn_valid() stays that way. + * Must be held any time you expect node_start_pfn, + * node_present_pages, node_spanned_pages or nr_zones stay constant. + * Holding this will also guarantee that any pfn_valid() stays that + * way. * * pgdat_resize_lock() and pgdat_resize_unlock() are provided to * manipulate node_size_lock without checking for CONFIG_MEMORY_HOTPLUG diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c index 61972da38d93..f626e7e5f57b 100644 --- a/mm/memory_hotplug.c +++ b/mm/memory_hotplug.c @@ -742,14 +742,13 @@ void __ref move_pfn_range_to_zone(struct zone *zone, unsigned long start_pfn, int nid = pgdat->node_id; unsigned long flags; - if (zone_is_empty(zone)) - init_currently_empty_zone(zone, start_pfn, nr_pages); - clear_zone_contiguous(zone); /* TODO Huh pgdat is irqsave while zone is not. It used to be like that before */ pgdat_resize_lock(pgdat, &flags); zone_span_writelock(zone); + if (zone_is_empty(zone)) + init_currently_empty_zone(zone, start_pfn, nr_pages); resize_zone_range(zone, start_pfn, nr_pages); zone_span_writeunlock(zone); resize_pgdat_range(pgdat, start_pfn, nr_pages);