linux-kernel - Re: [PATCH v2 2/2] mm: remove "count" parameter from has_unmovable

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Date:   Thu, 14 Nov 2019 20:40:44 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     David Hildenbrand <david@...hat.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linuxppc-dev@...ts.ozlabs.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        Oscar Salvador <osalvador@...e.de>,
        Anshuman Khandual <anshuman.khandual@....com>,
        Qian Cai <cai@....pw>, Pingfan Liu <kernelfans@...il.com>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Dan Williams <dan.j.williams@...el.com>,
        Pavel Tatashin <pasha.tatashin@...een.com>,
        Vlastimil Babka <vbabka@...e.cz>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>,
        Wei Yang <richardw.yang@...ux.intel.com>,
        Alexander Duyck <alexander.h.duyck@...ux.intel.com>,
        Alexander Potapenko <glider@...gle.com>,
        Arun KS <arunks@...eaurora.org>,
        Michael Ellerman <mpe@...erman.id.au>
Subject: Re: [PATCH v2 2/2] mm: remove "count" parameter from
 has_unmovable_pages()

On Thu 14-11-19 14:19:11, David Hildenbrand wrote:
> Now that the memory isolate notifier is gone, the parameter is always 0.
> Drop it and cleanup has_unmovable_pages().
> 
> Cc: Michal Hocko <mhocko@...e.com>
> Cc: Andrew Morton <akpm@...ux-foundation.org>
> Cc: Oscar Salvador <osalvador@...e.de>
> Cc: Anshuman Khandual <anshuman.khandual@....com>
> Cc: Qian Cai <cai@....pw>
> Cc: Pingfan Liu <kernelfans@...il.com>
> Cc: Stephen Rothwell <sfr@...b.auug.org.au>
> Cc: Dan Williams <dan.j.williams@...el.com>
> Cc: Pavel Tatashin <pasha.tatashin@...een.com>
> Cc: Vlastimil Babka <vbabka@...e.cz>
> Cc: Mel Gorman <mgorman@...hsingularity.net>
> Cc: Mike Rapoport <rppt@...ux.vnet.ibm.com>
> Cc: Wei Yang <richardw.yang@...ux.intel.com>
> Cc: Alexander Duyck <alexander.h.duyck@...ux.intel.com>
> Cc: Alexander Potapenko <glider@...gle.com>
> Cc: Arun KS <arunks@...eaurora.org>
> Cc: Michael Ellerman <mpe@...erman.id.au>
> Signed-off-by: David Hildenbrand <david@...hat.com>

yay again! I have to say that this was a head scratcher when I've seen
that for the first time. It is really great to see it go
Acked-by: Michal Hocko <mhocko@...e.com>

Thanks!

> ---
>  include/linux/page-isolation.h |  4 ++--
>  mm/memory_hotplug.c            |  2 +-
>  mm/page_alloc.c                | 21 +++++++--------------
>  mm/page_isolation.c            |  2 +-
>  4 files changed, 11 insertions(+), 18 deletions(-)
> 
> diff --git a/include/linux/page-isolation.h b/include/linux/page-isolation.h
> index 6861df759fad..148e65a9c606 100644
> --- a/include/linux/page-isolation.h
> +++ b/include/linux/page-isolation.h
> @@ -33,8 +33,8 @@ static inline bool is_migrate_isolate(int migratetype)
>  #define MEMORY_OFFLINE	0x1
>  #define REPORT_FAILURE	0x2
>  
> -bool has_unmovable_pages(struct zone *zone, struct page *page, int count,
> -			 int migratetype, int flags);
> +bool has_unmovable_pages(struct zone *zone, struct page *page, int migratetype,
> +			 int flags);
>  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/memory_hotplug.c b/mm/memory_hotplug.c
> index 3b5cee4d3f4e..f06d33748607 100644
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -1158,7 +1158,7 @@ static bool is_pageblock_removable_nolock(unsigned long pfn)
>  	if (!zone_spans_pfn(zone, pfn))
>  		return false;
>  
> -	return !has_unmovable_pages(zone, page, 0, MIGRATE_MOVABLE,
> +	return !has_unmovable_pages(zone, page, MIGRATE_MOVABLE,
>  				    MEMORY_OFFLINE);
>  }
>  
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index f5ecbacb0e04..e4d8f3a1a6b6 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -8270,17 +8270,15 @@ void *__init alloc_large_system_hash(const char *tablename,
>  
>  /*
>   * This function checks whether pageblock includes unmovable pages or not.
> - * If @count is not zero, it is okay to include less @count unmovable pages
>   *
>   * PageLRU check without isolation or lru_lock could race so that
>   * MIGRATE_MOVABLE block might include unmovable pages. And __PageMovable
>   * check without lock_page also may miss some movable non-lru pages at
>   * 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, int flags)
> +bool has_unmovable_pages(struct zone *zone, struct page *page, int migratetype,
> +			 int flags)
>  {
> -	unsigned long found;
>  	unsigned long iter = 0;
>  	unsigned long pfn = page_to_pfn(page);
>  	const char *reason = "unmovable page";
> @@ -8306,13 +8304,11 @@ bool has_unmovable_pages(struct zone *zone, struct page *page, int count,
>  		goto unmovable;
>  	}
>  
> -	for (found = 0; iter < pageblock_nr_pages; iter++) {
> -		unsigned long check = pfn + iter;
> -
> -		if (!pfn_valid_within(check))
> +	for (; iter < pageblock_nr_pages; iter++) {
> +		if (!pfn_valid_within(pfn + iter))
>  			continue;
>  
> -		page = pfn_to_page(check);
> +		page = pfn_to_page(pfn + iter);
>  
>  		if (PageReserved(page))
>  			goto unmovable;
> @@ -8361,11 +8357,9 @@ bool has_unmovable_pages(struct zone *zone, struct page *page, int count,
>  		if ((flags & MEMORY_OFFLINE) && PageHWPoison(page))
>  			continue;
>  
> -		if (__PageMovable(page))
> +		if (__PageMovable(page) || PageLRU(page))
>  			continue;
>  
> -		if (!PageLRU(page))
> -			found++;
>  		/*
>  		 * If there are RECLAIMABLE pages, we need to check
>  		 * it.  But now, memory offline itself doesn't call
> @@ -8379,8 +8373,7 @@ bool has_unmovable_pages(struct zone *zone, struct page *page, int count,
>  		 * is set to both of a memory hole page and a _used_ kernel
>  		 * page at boot.
>  		 */
> -		if (found > count)
> -			goto unmovable;
> +		goto unmovable;
>  	}
>  	return false;
>  unmovable:
> diff --git a/mm/page_isolation.c b/mm/page_isolation.c
> index 21af88b718aa..1f8b9dfecbe8 100644
> --- a/mm/page_isolation.c
> +++ b/mm/page_isolation.c
> @@ -37,7 +37,7 @@ static int set_migratetype_isolate(struct page *page, int migratetype, int isol_
>  	 * FIXME: Now, memory hotplug doesn't call shrink_slab() by itself.
>  	 * We just check MOVABLE pages.
>  	 */
> -	if (!has_unmovable_pages(zone, page, 0, migratetype, isol_flags)) {
> +	if (!has_unmovable_pages(zone, page, migratetype, isol_flags)) {
>  		unsigned long nr_pages;
>  		int mt = get_pageblock_migratetype(page);
>  
> -- 
> 2.21.0

-- 
Michal Hocko
SUSE Labs