linux-kernel - Re: [PATCH 7/8] mm: drop page_index/page_file_offset and convert swap helpers to use folio

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Date: Thu, 18 Apr 2024 10:42:35 +0800
From: Kairui Song <ryncsn@...il.com>
To: Barry Song <21cnbao@...il.com>
Cc: linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>, 
	"Huang, Ying" <ying.huang@...el.com>, Matthew Wilcox <willy@...radead.org>, Chris Li <chrisl@...nel.org>, 
	Barry Song <v-songbaohua@...o.com>, Ryan Roberts <ryan.roberts@....com>, Neil Brown <neilb@...e.de>, 
	Minchan Kim <minchan@...nel.org>, Hugh Dickins <hughd@...gle.com>, 
	David Hildenbrand <david@...hat.com>, Yosry Ahmed <yosryahmed@...gle.com>, linux-fsdevel@...r.kernel.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 7/8] mm: drop page_index/page_file_offset and convert swap
 helpers to use folio

On Thu, Apr 18, 2024 at 9:55 AM Barry Song <21cnbao@...il.com> wrote:
>
> On Thu, Apr 18, 2024 at 4:12 AM Kairui Song <ryncsn@...il.com> wrote:
> >
> > From: Kairui Song <kasong@...cent.com>
> >
> > When applied on swap cache pages, page_index / page_file_offset was used
> > to retrieve the swap cache index or swap file offset of a page, and they
> > have their folio equivalence version: folio_index / folio_file_pos.
> >
> > We have eliminated all users for page_index / page_file_offset, everything
> > is using folio_index / folio_file_pos now, so remove the old helpers.
> >
> > Then convert the implementation of folio_index / folio_file_pos to
> > to use folio natively.
> >
> > After this commit, all users that might encounter mixed usage of swap
> > cache and page cache will only use following two helpers:
> >
> > folio_index (calls __folio_swap_cache_index)
> > folio_file_pos (calls __folio_swap_file_pos)
> >
> > The offset in swap file and index in swap cache is still basically the
> > same thing at this moment, but will be different in following commits.
> >
> > Signed-off-by: Kairui Song <kasong@...cent.com>
>
> Hi Kairui, thanks !
>
> I also find it rather odd that folio_file_page() is utilized for both
> swp and file.
>
> mm/memory.c <<do_swap_page>>
>              page = folio_file_page(folio, swp_offset(entry));
> mm/swap_state.c <<swapin_readahead>>
>              return folio_file_page(folio, swp_offset(entry));
> mm/swapfile.c <<unuse_pte>>
>              page = folio_file_page(folio, swp_offset(entry));
>
> Do you believe it's worthwhile to tidy up?
>

Hi Barry,

I'm not sure about this. Using folio_file_page doesn't look too bad,
and it will be gone once we convert them to always use folio, this
shouldn't take too long.