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From: Vlastimil Babka <vbabka@suse.cz>
To: Minchan Kim <minchan@kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>
Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org,
	Rik van Riel <riel@redhat.com>,
	Joonsoo Kim <iamjoonsoo.kim@lge.com>,
	Mel Gorman <mgorman@suse.de>, Hugh Dickins <hughd@google.com>,
	Rafael Aquini <aquini@redhat.com>,
	virtualization@lists.linux-foundation.org,
	Jonathan Corbet <corbet@lwn.net>,
	John Einar Reitan <john.reitan@foss.arm.com>,
	dri-devel@lists.freedesktop.org,
	Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
	Gioh Kim <gi-oh.kim@profitbricks.com>
Subject: Re: PATCH v6v2 02/12] mm: migrate: support non-lru movable page migration
Date: Mon, 30 May 2016 11:36:07 +0200	[thread overview]
Message-ID: <2bc277c4-4257-c6cb-2e37-ee5de985410b@suse.cz> (raw)
In-Reply-To: <20160530013926.GB8683@bbox>

On 05/30/2016 03:39 AM, Minchan Kim wrote:
> After isolation, VM calls migratepage of driver with isolated page.
> The function of migratepage is to move content of the old page to new page
> and set up fields of struct page newpage. Keep in mind that you should
> clear PG_movable of oldpage via __ClearPageMovable under page_lock if you
> migrated the oldpage successfully and returns 0.

This "clear PG_movable" is one of the reasons I was confused about what 
__ClearPageMovable() really does. There's no actual "PG_movable" page 
flag and the function doesn't clear even the actual mapping flag :) Also 
same thing in the Documentation/ part.

Something like "... you should indicate to the VM that the oldpage is no 
longer movable via __ClearPageMovable() ..."?

> --- a/mm/compaction.c
> +++ b/mm/compaction.c
> @@ -81,6 +81,39 @@ static inline bool migrate_async_suitable(int migratetype)
>
>  #ifdef CONFIG_COMPACTION
>
> +int PageMovable(struct page *page)
> +{
> +	struct address_space *mapping;
> +
> +	VM_BUG_ON_PAGE(!PageLocked(page), page);
> +	if (!__PageMovable(page))
> +		return 0;
> +
> +	mapping = page_mapping(page);
> +	if (mapping && mapping->a_ops && mapping->a_ops->isolate_page)
> +		return 1;
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL(PageMovable);
> +
> +void __SetPageMovable(struct page *page, struct address_space *mapping)
> +{
> +	VM_BUG_ON_PAGE(!PageLocked(page), page);
> +	VM_BUG_ON_PAGE((unsigned long)mapping & PAGE_MAPPING_MOVABLE, page);
> +	page->mapping = (void *)((unsigned long)mapping | PAGE_MAPPING_MOVABLE);
> +}
> +EXPORT_SYMBOL(__SetPageMovable);
> +
> +void __ClearPageMovable(struct page *page)
> +{
> +	VM_BUG_ON_PAGE(!PageLocked(page), page);
> +	VM_BUG_ON_PAGE(!PageMovable(page), page);
> +	page->mapping = (void *)((unsigned long)page->mapping &
> +				PAGE_MAPPING_MOVABLE);
> +}
> +EXPORT_SYMBOL(__ClearPageMovable);

The second confusing thing is that the function is named 
__ClearPageMovable(), but what it really clears is the mapping pointer,
which is not at all the opposite of what __SetPageMovable() does.

I know it's explained in the documentation, but it also deserves a 
comment here so it doesn't confuse everyone who looks at it.
Even better would be a less confusing name for the function, but I can't 
offer one right now.

> diff --git a/mm/util.c b/mm/util.c
> index 917e0e3d0f8e..b756ee36f7f0 100644
> --- a/mm/util.c
> +++ b/mm/util.c
> @@ -399,10 +399,12 @@ struct address_space *page_mapping(struct page *page)
>  	}
>
>  	mapping = page->mapping;

I'd probably use READ_ONCE() here to be safe. Not all callers are under 
page lock?

> -	if ((unsigned long)mapping & PAGE_MAPPING_FLAGS)
> +	if ((unsigned long)mapping & PAGE_MAPPING_ANON)
>  		return NULL;
> -	return mapping;
> +
> +	return (void *)((unsigned long)mapping & ~PAGE_MAPPING_FLAGS);
>  }
> +EXPORT_SYMBOL(page_mapping);
>
>  /* Slow path of page_mapcount() for compound pages */
>  int __page_mapcount(struct page *page)
>

  reply	other threads:[~2016-05-30  9:36 UTC|newest]

Thread overview: 44+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-05-20 14:23 [PATCH v6 00/12] Support non-lru page migration Minchan Kim
2016-05-20 14:23 ` [PATCH v6 01/12] mm: use put_page to free page instead of putback_lru_page Minchan Kim
2016-05-20 14:23 ` [PATCH v6 02/12] mm: migrate: support non-lru movable page migration Minchan Kim
2016-05-27 14:26   ` Vlastimil Babka
2016-05-30  1:33     ` Minchan Kim
2016-05-30  9:01       ` Vlastimil Babka
2016-05-30  1:39   ` PATCH v6v2 " Minchan Kim
2016-05-30  9:36     ` Vlastimil Babka [this message]
2016-05-30 16:25       ` Minchan Kim
2016-05-31  7:51         ` Vlastimil Babka
2016-05-31  0:01     ` [PATCH v6v3 " Minchan Kim
2016-05-31  7:52       ` Vlastimil Babka
2016-05-31 23:05         ` Minchan Kim
2016-06-13  9:38       ` Anshuman Khandual
2016-06-15  2:32         ` Minchan Kim
2016-06-15  6:45           ` Anshuman Khandual
2016-06-16  0:26             ` Minchan Kim
2016-06-16  3:42               ` Anshuman Khandual
2016-06-16  5:37                 ` Minchan Kim
2016-06-27  5:51                   ` Anshuman Khandual
2016-06-28  6:39                     ` Minchan Kim
2016-06-30  5:56                       ` Anshuman Khandual
2016-06-30  6:18                         ` Minchan Kim
2016-05-20 14:23 ` [PATCH v6 03/12] mm: balloon: use general non-lru movable page feature Minchan Kim
2016-05-30 12:16   ` Vlastimil Babka
2016-05-20 14:23 ` [PATCH v6 04/12] zsmalloc: keep max_object in size_class Minchan Kim
2016-05-20 14:23 ` [PATCH v6 05/12] zsmalloc: use bit_spin_lock Minchan Kim
2016-05-20 14:23 ` [PATCH v6 06/12] zsmalloc: use accessor Minchan Kim
2016-05-20 14:23 ` [PATCH v6 07/12] zsmalloc: factor page chain functionality out Minchan Kim
2016-05-20 14:23 ` [PATCH v6 08/12] zsmalloc: introduce zspage structure Minchan Kim
2016-05-20 14:23 ` [PATCH v6 09/12] zsmalloc: separate free_zspage from putback_zspage Minchan Kim
2016-05-20 14:23 ` [PATCH v6 10/12] zsmalloc: use freeobj for index Minchan Kim
2016-05-20 14:23 ` [PATCH v6 11/12] zsmalloc: page migration support Minchan Kim
2016-05-24  5:28   ` Sergey Senozhatsky
2016-05-24  6:28     ` Minchan Kim
2016-05-24  8:05       ` Sergey Senozhatsky
2016-05-24  8:17         ` Minchan Kim
2016-05-25  5:14       ` Minchan Kim
2016-05-25 15:23         ` Sergey Senozhatsky
2016-05-26  0:32           ` Minchan Kim
2016-05-26  0:59             ` Sergey Senozhatsky
2016-05-26  4:37               ` Minchan Kim
2016-05-26 21:50   ` [PATCH v6r2 " Minchan Kim
2016-05-20 14:23 ` [PATCH v6 12/12] zram: use __GFP_MOVABLE for memory allocation Minchan Kim

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