Re: [PATCH 3/4] mm: unify new_node_page and alloc_migrate_target

[Michal Hocko <mhocko@kernel.org>]

On Thu 08-06-17 10:36:13, Vlastimil Babka wrote:
> On 06/08/2017 09:45 AM, Michal Hocko wrote:
> > From: Michal Hocko <mhocko@suse.com>
> > 
> > 394e31d2ceb4 ("mem-hotplug: alloc new page from a nearest neighbor node
> > when mem-offline") has duplicated a large part of alloc_migrate_target
> > with some hotplug specific special casing. To be more precise it tried
> > to enfore the allocation from a different node than the original page.
> > As a result the two function diverged in their shared logic, e.g. the
> > hugetlb allocation strategy. Let's unify the two and express different
> > NUMA requirements by the given nodemask. new_node_page will simply
> > exclude the node it doesn't care about and alloc_migrate_target will
> > use all the available nodes. alloc_migrate_target will then learn to
> > migrate hugetlb pages more sanely and use preallocated pool when
> > possible.
> > 
> > Please note that alloc_migrate_target used to call alloc_page resp.
> > alloc_pages_current so the memory policy of the current context which
> > is quite strange when we consider that it is used in the context of
> > alloc_contig_range which just tries to migrate pages which stand in the
> > way.
> > 
> > Signed-off-by: Michal Hocko <mhocko@suse.com>
> 
> Acked-by: Vlastimil Babka <vbabka@suse.cz>

Thanks!

> > diff --git a/mm/page_isolation.c b/mm/page_isolation.c
> > index 3606104893e0..757410d9f758 100644
> > --- a/mm/page_isolation.c
> > +++ b/mm/page_isolation.c
> > @@ -8,6 +8,7 @@
> >  #include <linux/memory.h>
> >  #include <linux/hugetlb.h>
> >  #include <linux/page_owner.h>
> > +#include <linux/migrate.h>
> >  #include "internal.h"
> >  
> >  #define CREATE_TRACE_POINTS
> > @@ -294,20 +295,5 @@ int test_pages_isolated(unsigned long start_pfn, unsigned long end_pfn,
> >  struct page *alloc_migrate_target(struct page *page, unsigned long private,
> >  				  int **resultp)
> >  {
> > -	gfp_t gfp_mask = GFP_USER | __GFP_MOVABLE;
> > -
> > -	/*
> > -	 * TODO: allocate a destination hugepage from a nearest neighbor node,
> > -	 * accordance with memory policy of the user process if possible. For
> > -	 * now as a simple work-around, we use the next node for destination.
> > -	 */
> > -	if (PageHuge(page))
> > -		return alloc_huge_page_node(page_hstate(compound_head(page)),
> > -					    next_node_in(page_to_nid(page),
> > -							 node_online_map));
> > -
> > -	if (PageHighMem(page))
> > -		gfp_mask |= __GFP_HIGHMEM;
> > -
> > -	return alloc_page(gfp_mask);
> > +	return new_page_nodemask(page, numa_node_id(), &node_states[N_MEMORY]);
> 
> This replaces the N_ONLINE (node_online_map) with N_MEMORY for huge
> pages. Assuming that's OK.

Yes, this is what 231e97e2b8ec ("mem-hotplug: use nodes that contain
memory as mask in new_node_page()") fixed in new_node_page and didn't
care to do on alloc_migrate_target. Another argument to remove the code
duplication. Thanks for pointing out anyway!

-- 
Michal Hocko
SUSE Labs