Re: [PATCH v2 3/5] mm, memory_hotplug: Move zone/pages handling to offline stage

[Mike Rapoport <rppt@linux.ibm.com>]

On Tue, Nov 27, 2018 at 05:20:03PM +0100, Oscar Salvador wrote:
> From: Oscar Salvador <osalvador@suse.com>
> 
> The current implementation accesses pages during hot-remove
> stage in order to get the zone linked to this memory-range.
> We use that zone for a) check if the zone is ZONE_DEVICE and
> b) to shrink the zone's spanned pages.
> 
> Accessing pages during this stage is problematic, as we might be
> accessing pages that were not initialized if we did not get to
> online the memory before removing it.
> 
> The only reason to check for ZONE_DEVICE in __remove_pages
> is to bypass the call to release_mem_region_adjustable(),
> since these regions are removed with devm_release_mem_region.
> 
> With patch#2, this is no longer a problem so we can safely
> call release_mem_region_adjustable().
> release_mem_region_adjustable() will spot that the region
> we are trying to remove was acquired by means of
> devm_request_mem_region, and will back off safely.
> 
> This allows us to remove all zone-related operations from
> hot-remove stage.
> 
> Because of this, zone's spanned pages are shrinked during
> the offlining stage in shrink_zone_pgdat().
> It would have been great to decrease also the spanned page
> for the node there, but we need them in try_offline_node().
> So we still decrease spanned pages for the node in the hot-remove
> stage.
> 
> The only particularity is that now
> find_smallest_section_pfn/find_biggest_section_pfn, when called from
> shrink_zone_span, will now check for online sections and not
> valid sections instead.
> To make this work with devm/HMM code, we need to call offline_mem_sections
> and online_mem_sections in that code path when we are adding memory.
> 
> Signed-off-by: Oscar Salvador <osalvador@suse.de>
> ---
>  arch/powerpc/mm/mem.c          | 11 +----
>  arch/sh/mm/init.c              |  4 +-
>  arch/x86/mm/init_32.c          |  3 +-
>  arch/x86/mm/init_64.c          |  8 +---
>  include/linux/memory_hotplug.h |  8 ++--
>  kernel/memremap.c              | 14 +++++--
>  mm/memory_hotplug.c            | 95 ++++++++++++++++++++++++------------------
>  mm/sparse.c                    |  4 +-
>  8 files changed, 76 insertions(+), 71 deletions(-)
 
[ ... ]
 
>  /**
> - * __remove_pages() - remove sections of pages from a zone
> - * @zone: zone from which pages need to be removed
> + * __remove_pages() - remove sections of pages from a nid
> + * @nid: nid from which pages belong to

Nit: the description sounds a bit awkward.
Why not to keep the original one with s/zone/node/?

>   * @phys_start_pfn: starting pageframe (must be aligned to start of a section)
>   * @nr_pages: number of pages to remove (must be multiple of section size)
>   * @altmap: alternative device page map or %NULL if default memmap is used
> @@ -547,35 +566,28 @@ static int __remove_section(struct zone *zone, struct mem_section *ms,
>   * sure that pages are marked reserved and zones are adjust properly by
>   * calling offline_pages().
>   */

-- 
Sincerely yours,
Mike.