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Date:   Thu, 26 Oct 2017 15:59:32 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-mm@...ck.org, Michael Ellerman <mpe@...erman.id.au>,
        Vlastimil Babka <vbabka@...e.cz>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
        Reza Arbab <arbab@...ux.vnet.ibm.com>,
        Yasuaki Ishimatsu <yasu.isimatu@...il.com>,
        qiuxishi@...wei.com, Igor Mammedov <imammedo@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] mm: drop migrate type checks from has_unmovable_pages

On Thu 19-10-17 14:21:18, Michal Hocko wrote:
[...]
> From 8cbd811d741f5dd93d1b21bb3ef94482a4d0bd32 Mon Sep 17 00:00:00 2001
> From: Michal Hocko <mhocko@...e.com>
> Date: Thu, 19 Oct 2017 14:14:02 +0200
> Subject: [PATCH] mm: distinguish CMA and MOVABLE isolation in
>  has_unmovable_pages
> 
> Joonsoo has noticed that "mm: drop migrate type checks from
> has_unmovable_pages" would break CMA allocator because it relies on
> has_unmovable_pages returning false even for CMA pageblocks which in
> fact don't have to be movable:
> alloc_contig_range
>   start_isolate_page_range
>     set_migratetype_isolate
>       has_unmovable_pages
> 
> This is a result of the code sharing between CMA and memory hotplug
> while each one has a different idea of what has_unmovable_pages should
> return. This is unfortunate but fixing it properly would require a lot
> of code duplication.
> 
> Fix the issue by introducing the requested migrate type argument
> and special case MIGRATE_CMA case where CMA page blocks are handled
> properly. This will work for memory hotplug because it requires
> MIGRATE_MOVABLE.
> 
> Reported-by: Joonsoo Kim <iamjoonsoo.kim@....com>
> Signed-off-by: Michal Hocko <mhocko@...e.com>
> ---

Andrew,
could you add this one to the bundle as well? After
mm-drop-migrate-type-checks-from-has_unmovable_pages.patch, please.

Joonsoo would like to see a larger change in this area [1] but I think
we need to think those much more through [2] and Joonsoo agreed to take
the simpler patch first [3].

Thanks!

[1] http://lkml.kernel.org/r/20171024044423.GA31424@js1304-P5Q-DELUXE
[2] http://lkml.kernel.org/r/20171024122526.3kmabkcbmj4johli@dhcp22.suse.cz
[3] http://lkml.kernel.org/r/20171026024707.GA11791@js1304-P5Q-DELUXE

>  include/linux/page-isolation.h |  2 +-
>  mm/page_alloc.c                | 12 +++++++++++-
>  mm/page_isolation.c            | 10 +++++-----
>  3 files changed, 17 insertions(+), 7 deletions(-)
> 
> diff --git a/include/linux/page-isolation.h b/include/linux/page-isolation.h
> index d4cd2014fa6f..fa9db0c7b54e 100644
> --- a/include/linux/page-isolation.h
> +++ b/include/linux/page-isolation.h
> @@ -30,7 +30,7 @@ static inline bool is_migrate_isolate(int migratetype)
>  #endif
>  
>  bool has_unmovable_pages(struct zone *zone, struct page *page, int count,
> -			 bool skip_hwpoisoned_pages);
> +			 int migratetype, bool skip_hwpoisoned_pages);
>  void set_pageblock_migratetype(struct page *page, int migratetype);
>  int move_freepages_block(struct zone *zone, struct page *page,
>  				int migratetype, int *num_movable);
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 5b4d85ae445c..259aeb22462f 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -7344,6 +7344,7 @@ void *__init alloc_large_system_hash(const char *tablename,
>   * race condition. So you can't expect this function should be exact.
>   */
>  bool has_unmovable_pages(struct zone *zone, struct page *page, int count,
> +			 int migratetype,
>  			 bool skip_hwpoisoned_pages)
>  {
>  	unsigned long pfn, iter, found;
> @@ -7356,6 +7357,15 @@ bool has_unmovable_pages(struct zone *zone, struct page *page, int count,
>  	if (zone_idx(zone) == ZONE_MOVABLE)
>  		return false;
>  
> +	/*
> +	 * CMA allocations (alloc_contig_range) really need to mark isolate
> +	 * CMA pageblocks even when they are not movable in fact so consider
> +	 * them movable here.
> +	 */
> +	if (is_migrate_cma(migratetype) &&
> +			is_migrate_cma(get_pageblock_migratetype(page)))
> +		return false;
> +
>  	pfn = page_to_pfn(page);
>  	for (found = 0, iter = 0; iter < pageblock_nr_pages; iter++) {
>  		unsigned long check = pfn + iter;
> @@ -7441,7 +7451,7 @@ bool is_pageblock_removable_nolock(struct page *page)
>  	if (!zone_spans_pfn(zone, pfn))
>  		return false;
>  
> -	return !has_unmovable_pages(zone, page, 0, true);
> +	return !has_unmovable_pages(zone, page, 0, MIGRATE_MOVABLE, true);
>  }
>  
>  #if (defined(CONFIG_MEMORY_ISOLATION) && defined(CONFIG_COMPACTION)) || defined(CONFIG_CMA)
> diff --git a/mm/page_isolation.c b/mm/page_isolation.c
> index 757410d9f758..8616f5332c77 100644
> --- a/mm/page_isolation.c
> +++ b/mm/page_isolation.c
> @@ -14,7 +14,7 @@
>  #define CREATE_TRACE_POINTS
>  #include <trace/events/page_isolation.h>
>  
> -static int set_migratetype_isolate(struct page *page,
> +static int set_migratetype_isolate(struct page *page, int migratetype,
>  				bool skip_hwpoisoned_pages)
>  {
>  	struct zone *zone;
> @@ -51,7 +51,7 @@ static int set_migratetype_isolate(struct page *page,
>  	 * FIXME: Now, memory hotplug doesn't call shrink_slab() by itself.
>  	 * We just check MOVABLE pages.
>  	 */
> -	if (!has_unmovable_pages(zone, page, arg.pages_found,
> +	if (!has_unmovable_pages(zone, page, arg.pages_found, migratetype,
>  				 skip_hwpoisoned_pages))
>  		ret = 0;
>  
> @@ -63,14 +63,14 @@ static int set_migratetype_isolate(struct page *page,
>  out:
>  	if (!ret) {
>  		unsigned long nr_pages;
> -		int migratetype = get_pageblock_migratetype(page);
> +		int mt = get_pageblock_migratetype(page);
>  
>  		set_pageblock_migratetype(page, MIGRATE_ISOLATE);
>  		zone->nr_isolate_pageblock++;
>  		nr_pages = move_freepages_block(zone, page, MIGRATE_ISOLATE,
>  									NULL);
>  
> -		__mod_zone_freepage_state(zone, -nr_pages, migratetype);
> +		__mod_zone_freepage_state(zone, -nr_pages, mt);
>  	}
>  
>  	spin_unlock_irqrestore(&zone->lock, flags);
> @@ -182,7 +182,7 @@ int start_isolate_page_range(unsigned long start_pfn, unsigned long end_pfn,
>  	     pfn += pageblock_nr_pages) {
>  		page = __first_valid_page(pfn, pageblock_nr_pages);
>  		if (page &&
> -		    set_migratetype_isolate(page, skip_hwpoisoned_pages)) {
> +		    set_migratetype_isolate(page, migratetype, skip_hwpoisoned_pages)) {
>  			undo_pfn = pfn;
>  			goto undo;
>  		}
> -- 
> 2.14.2
> 
> -- 
> Michal Hocko
> SUSE Labs

-- 
Michal Hocko
SUSE Labs

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