linux-kernel - Re: [RFC PATCH 2/3] mm/memory_hotplug: Create __shrink_pages and move it to offline

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Date:   Tue, 7 Aug 2018 16:59:00 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Jerome Glisse <jglisse@...hat.com>
Cc:     osalvador@...hadventures.net, akpm@...ux-foundation.org,
        dan.j.williams@...el.com, pasha.tatashin@...cle.com,
        david@...hat.com, yasu.isimatu@...il.com, logang@...tatee.com,
        dave.jiang@...el.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Oscar Salvador <osalvador@...e.de>
Subject: Re: [RFC PATCH 2/3] mm/memory_hotplug: Create __shrink_pages and
 move it to offline_pages

On Tue 07-08-18 09:52:21, Jerome Glisse wrote:
> On Tue, Aug 07, 2018 at 03:37:56PM +0200, osalvador@...hadventures.net wrote:
> > From: Oscar Salvador <osalvador@...e.de>
> 
> [...]
> 
> > diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c
> > index 9bd629944c91..e33555651e46 100644
> > --- a/mm/memory_hotplug.c
> > +++ b/mm/memory_hotplug.c
> 
> [...]
> 
> >  /**
> >   * __remove_pages() - remove sections of pages from a zone
> > - * @zone: zone from which pages need to be removed
> > + * @nid: node which pages belong to
> >   * @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
> > @@ -548,7 +557,7 @@ 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().
> >   */
> > -int __remove_pages(struct zone *zone, unsigned long phys_start_pfn,
> > +int __remove_pages(int nid, unsigned long phys_start_pfn,
> >  		 unsigned long nr_pages, struct vmem_altmap *altmap)
> >  {
> >  	unsigned long i;
> > @@ -556,10 +565,9 @@ int __remove_pages(struct zone *zone, unsigned long phys_start_pfn,
> >  	int sections_to_remove, ret = 0;
> >  
> >  	/* In the ZONE_DEVICE case device driver owns the memory region */
> > -	if (is_dev_zone(zone)) {
> > -		if (altmap)
> > -			map_offset = vmem_altmap_offset(altmap);
> > -	} else {
> > +	if (altmap)
> > +		map_offset = vmem_altmap_offset(altmap);
> > +	else {
> 
> This will break ZONE_DEVICE at least for HMM. While i think that
> altmap -> ZONE_DEVICE (ie altmap imply ZONE_DEVICE) the reverse
> is not true ie ZONE_DEVICE does not necessarily imply altmap. So
> with the above changes you change the expected behavior.

Could you be more specific what is the expected behavior here?
Is this about calling release_mem_region_adjustable? Why does is it not
suitable for zone device ranges?
-- 
Michal Hocko
SUSE Labs