linux-kernel - Re: [PATCH 3/3] mm: Enable Buddy allocation isolation for CDM nodes

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Message-ID: <8ef1de25-d4fd-482c-c55e-df93d0730484@suse.cz>
Date:   Wed, 8 Feb 2017 18:18:09 +0100
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Anshuman Khandual <khandual@...ux.vnet.ibm.com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Cc:     mhocko@...e.com, mgorman@...e.de, minchan@...nel.org,
        aneesh.kumar@...ux.vnet.ibm.com, bsingharora@...il.com,
        srikar@...ux.vnet.ibm.com, haren@...ux.vnet.ibm.com,
        jglisse@...hat.com, dave.hansen@...el.com, dan.j.williams@...el.com
Subject: Re: [PATCH 3/3] mm: Enable Buddy allocation isolation for CDM nodes

On 02/08/2017 03:01 PM, Anshuman Khandual wrote:
> This implements allocation isolation for CDM nodes in buddy allocator by
> discarding CDM memory zones all the time except in the cases where the gfp
> flag has got __GFP_THISNODE or the nodemask contains CDM nodes in cases
> where it is non NULL (explicit allocation request in the kernel or user
> process MPOL_BIND policy based requests).
>
> Signed-off-by: Anshuman Khandual <khandual@...ux.vnet.ibm.com>
> ---
>  mm/page_alloc.c | 19 +++++++++++++++++++
>  1 file changed, 19 insertions(+)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 40908de..7d8c82a 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -64,6 +64,7 @@
>  #include <linux/page_owner.h>
>  #include <linux/kthread.h>
>  #include <linux/memcontrol.h>
> +#include <linux/node.h>
>
>  #include <asm/sections.h>
>  #include <asm/tlbflush.h>
> @@ -2908,6 +2909,24 @@ get_page_from_freelist(gfp_t gfp_mask, unsigned int order, int alloc_flags,
>  		struct page *page;
>  		unsigned long mark;
>
> +		/*
> +		 * CDM nodes get skipped if the requested gfp flag
> +		 * does not have __GFP_THISNODE set or the nodemask
> +		 * does not have any CDM nodes in case the nodemask
> +		 * is non NULL (explicit allocation requests from
> +		 * kernel or user process MPOL_BIND policy which has
> +		 * CDM nodes).
> +		 */
> +		if (is_cdm_node(zone->zone_pgdat->node_id)) {
> +			if (!(gfp_mask & __GFP_THISNODE)) {
> +				if (!ac->nodemask)
> +					continue;
> +
> +				if (!nodemask_has_cdm(*ac->nodemask))
> +					continue;

nodemask_has_cdm() looks quite expensive, combined with the loop here that's 
O(n^2). But I don't understand why you need it. If there is no cdm node in the 
nodemask, then we never reach this code with a cdm node, because the zonelist 
iterator already checks the nodemask? Am I missing something?

> +			}
> +		}
> +
>  		if (cpusets_enabled() &&
>  			(alloc_flags & ALLOC_CPUSET) &&
>  			!__cpuset_zone_allowed(zone, gfp_mask))
>