On Tue, 19. Nov 12:52, David Hildenbrand wrote: > Our onlining/offlining code is unnecessarily complicated. Only memory > blocks added during boot can have holes (a range that is not > IORESOURCE_SYSTEM_RAM). Hotplugged memory never has holes (e.g., see > add_memory_resource()). All memory blocks that belong to boot memory are > already online. > > Note that boot memory can have holes and the memmap of the holes is marked > PG_reserved. However, also memory allocated early during boot is > PG_reserved - basically every page of boot memory that is not given to the > buddy is PG_reserved. > > Therefore, when we stop allowing to offline memory blocks with holes, we > implicitly no longer have to deal with onlining memory blocks with holes. > E.g., online_pages() will do a > walk_system_ram_range(..., online_pages_range), whereby > online_pages_range() will effectively only free the memory holes not > falling into a hole to the buddy. The other pages (holes) are kept > PG_reserved (via move_pfn_range_to_zone()->memmap_init_zone()). > > This allows to simplify the code. For example, we no longer have to > worry about marking pages that fall into memory holes PG_reserved when > onlining memory. We can stop setting pages PG_reserved completely in > memmap_init_zone(). > > Offlining memory blocks added during boot is usually not guaranteed to work > either way (unmovable data might have easily ended up on that memory during > boot). So stopping to do that should not really hurt. Also, people are not > even aware of a setup where onlining/offlining of memory blocks with > holes used to work reliably (see [1] and [2] especially regarding the > hotplug path) - I doubt it worked reliably. > > For the use case of offlining memory to unplug DIMMs, we should see no > change. (holes on DIMMs would be weird). > > Please note that hardware errors (PG_hwpoison) are not memory holes and > are not affected by this change when offlining. > > [1] https://lkml.org/lkml/2019/10/22/135 > [2] https://lkml.org/lkml/2019/8/14/1365 > > Reviewed-by: Dan Williams <dan.j.williams@xxxxxxxxx> > Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> > Cc: Michal Hocko <mhocko@xxxxxxxx> > Cc: Oscar Salvador <osalvador@xxxxxxx> > Cc: Pavel Tatashin <pasha.tatashin@xxxxxxxxxx> > Cc: Dan Williams <dan.j.williams@xxxxxxxxx> > Cc: Anshuman Khandual <anshuman.khandual@xxxxxxx> > Signed-off-by: David Hildenbrand <david@xxxxxxxxxx> > --- > > This patch was part of: > [PATCH v1 00/10] mm: Don't mark hotplugged pages PG_reserved > (including ZONE_DEVICE) > -> https://www.spinics.net/lists/linux-driver-devel/msg130042.html > > However, before we can perform the PG_reserved changes, we have to fix > pfn_to_online_page() in special scenarios first (bootmem and devmem falling > into a single section). Dan is working on that. > > I propose to give this patch a churn in -next so we can identify if this > change would break any existing setup. I will then follow up with cleanups > and the PG_reserved changes later. > > --- > mm/memory_hotplug.c | 28 ++++++++++++++++++++++++++-- > 1 file changed, 26 insertions(+), 2 deletions(-) > > diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c > index 46b2e056a43f..fc617ad6f035 100644 > --- a/mm/memory_hotplug.c > +++ b/mm/memory_hotplug.c > @@ -1455,10 +1455,19 @@ static void node_states_clear_node(int node, struct memory_notify *arg) > node_clear_state(node, N_MEMORY); > } > > +static int count_system_ram_pages_cb(unsigned long start_pfn, > + unsigned long nr_pages, void *data) > +{ > + unsigned long *nr_system_ram_pages = data; > + > + *nr_system_ram_pages += nr_pages; > + return 0; > +} > + Hello David, what is the meaning of the function ? The return is every time 0. I dont understand it ? Best regards Damian > static int __ref __offline_pages(unsigned long start_pfn, > unsigned long end_pfn) > { > - unsigned long pfn, nr_pages; > + unsigned long pfn, nr_pages = 0; > unsigned long offlined_pages = 0; > int ret, node, nr_isolate_pageblock; > unsigned long flags; > @@ -1469,6 +1478,22 @@ static int __ref __offline_pages(unsigned long start_pfn, > > mem_hotplug_begin(); > > + /* > + * Don't allow to offline memory blocks that contain holes. > + * Consequently, memory blocks with holes can never get onlined > + * via the hotplug path - online_pages() - as hotplugged memory has > + * no holes. This way, we e.g., don't have to worry about marking > + * memory holes PG_reserved, don't need pfn_valid() checks, and can > + * avoid using walk_system_ram_range() later. > + */ > + walk_system_ram_range(start_pfn, end_pfn - start_pfn, &nr_pages, > + count_system_ram_pages_cb); > + if (nr_pages != end_pfn - start_pfn) { > + ret = -EINVAL; > + reason = "memory holes"; > + goto failed_removal; > + } > + > /* This makes hotplug much easier...and readable. > we assume this for now. .*/ > if (!test_pages_in_a_zone(start_pfn, end_pfn, &valid_start, > @@ -1480,7 +1505,6 @@ static int __ref __offline_pages(unsigned long start_pfn, > > zone = page_zone(pfn_to_page(valid_start)); > node = zone_to_nid(zone); > - nr_pages = end_pfn - start_pfn; > > /* set above range as isolated */ > ret = start_isolate_page_range(start_pfn, end_pfn, > -- > 2.21.0 > >
