linux-kernel - Re: [PATCH v3 02/12] nilfs2: drop usage of page

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Date: Tue, 30 Apr 2024 04:28:41 +0900
From: Ryusuke Konishi <konishi.ryusuke@...il.com>
To: Kairui Song <ryncsn@...il.com>
Cc: Matthew Wilcox <willy@...radead.org>, linux-mm@...ck.org, 
	Andrew Morton <akpm@...ux-foundation.org>, "Huang, Ying" <ying.huang@...el.com>, 
	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, 
	linux-nilfs@...r.kernel.org
Subject: Re: [PATCH v3 02/12] nilfs2: drop usage of page_index

On Tue, Apr 30, 2024 at 4:22 AM Kairui Song <ryncsn@...il.com> wrote:
>
> On Tue, Apr 30, 2024 at 3:14 AM Matthew Wilcox <willy@...radead.org> wrote:
> >
> > On Tue, Apr 30, 2024 at 03:04:50AM +0800, Kairui Song wrote:
> > > From: Kairui Song <kasong@...cent.com>
> > >
> > > page_index is only for mixed usage of page cache and swap cache, for
> > > pure page cache usage, the caller can just use page->index instead.
> > >
> > > It can't be a swap cache page here (being part of buffer head),
> > > so just drop it, also convert it to use folio.
> > >
> > > Signed-off-by: Kairui Song <kasong@...cent.com>
> > > Cc: Ryusuke Konishi <konishi.ryusuke@...il.com>
> > > Cc: linux-nilfs@...r.kernel.org
> > > ---
> > >  fs/nilfs2/bmap.c | 5 ++---
> > >  1 file changed, 2 insertions(+), 3 deletions(-)
> > >
> > > diff --git a/fs/nilfs2/bmap.c b/fs/nilfs2/bmap.c
> > > index 383f0afa2cea..f4e5df0cd720 100644
> > > --- a/fs/nilfs2/bmap.c
> > > +++ b/fs/nilfs2/bmap.c
> > > @@ -453,9 +453,8 @@ __u64 nilfs_bmap_data_get_key(const struct nilfs_bmap *bmap,
> > >       struct buffer_head *pbh;
> > >       __u64 key;
> > >
> > > -     key = page_index(bh->b_page) << (PAGE_SHIFT -
> > > -                                      bmap->b_inode->i_blkbits);
> > > -     for (pbh = page_buffers(bh->b_page); pbh != bh; pbh = pbh->b_this_page)
> > > +     key = bh->b_folio->index << (PAGE_SHIFT - bmap->b_inode->i_blkbits);
> > > +     for (pbh = folio_buffers(bh->b_folio); pbh != bh; pbh = pbh->b_this_page)
> > >               key++;
> > >
> > >       return key;
> >
> > Why isn't this entire function simply:
> >
> >         return bh->b_blocknr;
> >
>
> Nice idea, I didn't plan for extra clean up and test for fs code, but
> this might be OK to have, will check it.

Wait a minute.

This function returns a key that corresponds to the cache offset of
the data block, not the disk block number.

Why is returning to bh->b_blocknr an alternative ?
Am I missing something?

Ryusuke Konishi