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

[Vlastimil Babka <vbabka@suse.cz>]

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>

> 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.

>  }
>