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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CAKFNMokDR7oQxDH8WeUeJKm6GLDo54AnByYXxdAWHjiFeGWEwA@mail.gmail.com>
Date: Tue, 30 Apr 2024 05:01:25 +0900
From: Ryusuke Konishi <konishi.ryusuke@...il.com>
To: Matthew Wilcox <willy@...radead.org>, Kairui Song <ryncsn@...il.com>
Cc: 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 4:38 AM Matthew Wilcox wrote:
>
> On Tue, Apr 30, 2024 at 04:28:41AM +0900, Ryusuke Konishi wrote:
> > 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?
>
> Sorry, I forgot how b_blocknr was used.  What I meant was:
>
>         u64 key = bh->b_folio->index << (PAGE_SHIFT - bmap->b_inode->i_blkbits);
>
>         return key + bh_offset(bh) >> bmap->b_inode->i_blkbits;
>
> The point is to get rid of the loop.  We could simplify this (and make
> it ready for bs>PS) by doing:
>
>         loff_t pos = folio_pos(bh->b_folio) + bh_offset(bh);
>         return pos >> bmap->b_inode->i_blkbits;

I see, I understand the idea that it would be better to eliminate the loop.

The above conversion looks fine.
What are you going to do, Kairui ?

Thanks,
Ryusuke Konishi