linux-kernel - Re: [PATCH mm-unstable v1 1/4] mm/swap: stop using page->private on tail pages for THP

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Message-ID: <6f0a82a3-6948-20d9-580b-be1dbf415701@redhat.com>
Date:   Wed, 23 Aug 2023 14:15:06 +0200
From:   David Hildenbrand <david@...hat.com>
To:     linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-mm@...ck.org, linux-arm-kernel@...ts.infradead.org,
        Matthew Wilcox <willy@...radead.org>,
        Peter Xu <peterx@...hat.com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, Hugh Dickins <hughd@...gle.com>,
        Seth Jennings <sjenning@...hat.com>,
        Dan Streetman <ddstreet@...e.org>,
        Vitaly Wool <vitaly.wool@...sulko.com>
Subject: Re: [PATCH mm-unstable v1 1/4] mm/swap: stop using page->private on
 tail pages for THP_SWAP

On 21.08.23 18:08, David Hildenbrand wrote:
> Let's stop using page->private on tail pages, making it possible to
> just unconditionally reuse that field in the tail pages of large folios.
> 
> The remaining usage of the private field for THP_SWAP is in the THP
> splitting code (mm/huge_memory.c), that we'll handle separately later.
> 
> Update the THP_SWAP documentation and sanity checks in mm_types.h and
> __split_huge_page_tail().
> 
> Signed-off-by: David Hildenbrand <david@...hat.com>
> ---

@Andrew, the following change on top


 From 2b1fd10ef07c6d47aa9cd0ce10445ab1e1b97361 Mon Sep 17 00:00:00 2001
From: David Hildenbrand <david@...hat.com>
Date: Tue, 22 Aug 2023 19:16:55 +0200
Subject: [PATCH] fixup: mm/swap: stop using page->private on tail pages for
  THP_SWAP

Per Yoshry, use folio_page_idx(). It shouldn't make a difference for
our (THP) use case, but it's certainly cleaner.

Signed-off-by: David Hildenbrand <david@...hat.com>
---
  include/linux/swap.h | 2 +-
  1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/swap.h b/include/linux/swap.h
index 84fe0e94f5cd..e5cf58a1cf9e 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -344,7 +344,7 @@ static inline swp_entry_t page_swap_entry(struct page *page)
  	struct folio *folio = page_folio(page);
  	swp_entry_t entry = folio_swap_entry(folio);
  
-	entry.val += page - &folio->page;
+	entry.val += folio_page_idx(folio, page);
  	return entry;
  }
  
-- 
2.41.0


-- 
Cheers,

David / dhildenb