linux-kernel - Re: [PATCH] mm: unified folio_test_anon()/folio_anon

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Message-ID: <Zo_ZULOseAmEQMIw@casper.infradead.org>
Date: Thu, 11 Jul 2024 14:08:32 +0100
From: Matthew Wilcox <willy@...radead.org>
To: Yajun Deng <yajun.deng@...ux.dev>
Cc: akpm@...ux-foundation.org, david@...hat.com, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: unified folio_test_anon()/folio_anon_vma() and use
 them

On Thu, Jul 11, 2024 at 09:03:51PM +0800, Yajun Deng wrote:
> +++ b/include/linux/page-flags.h
> @@ -691,7 +691,8 @@ static __always_inline bool PageMappingFlags(const struct page *page)
>  
>  static __always_inline bool folio_test_anon(const struct folio *folio)
>  {
> -	return ((unsigned long)folio->mapping & PAGE_MAPPING_ANON) != 0;
> +	return ((unsigned long)folio->mapping & PAGE_MAPPING_FLAGS) ==
> +		PAGE_MAPPING_ANON;
>  }

This is wrong.  KSM pages are supposed to return true for
folio_test_anon().  I haven't looked any further at this patch, since
the premise appears to wrong and you clearly haven't tested.