linux-kernel - Re: [PATCH v7] iomap: make inline data support more flexible

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Message-ID: <YP60zLP13Hqi5iL+@B-P7TQMD6M-0146.local>
Date:   Mon, 26 Jul 2021 21:12:44 +0800
From:   Gao Xiang <hsiangkao@...ux.alibaba.com>
To:     Andreas Gruenbacher <agruenba@...hat.com>
Cc:     Matthew Wilcox <willy@...radead.org>,
        Christoph Hellwig <hch@....de>,
        "Darrick J . Wong" <djwong@...nel.org>,
        Huang Jianan <huangjianan@...o.com>,
        linux-erofs@...ts.ozlabs.org,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Andreas Gruenbacher <andreas.gruenbacher@...il.com>
Subject: Re: [PATCH v7] iomap: make inline data support more flexible

On Mon, Jul 26, 2021 at 03:03:14PM +0200, Andreas Gruenbacher wrote:
> On Mon, Jul 26, 2021 at 2:33 PM Matthew Wilcox <willy@...radead.org> wrote:
> > On Mon, Jul 26, 2021 at 01:06:11PM +0200, Andreas Gruenbacher wrote:
> > > @@ -671,11 +683,11 @@ static size_t iomap_write_end_inline(struct inode *inode, struct page *page,
> > >       void *addr;
> > >
> > >       WARN_ON_ONCE(!PageUptodate(page));
> > > -     BUG_ON(pos + copied > PAGE_SIZE - offset_in_page(iomap->inline_data));
> > > +     BUG_ON(!iomap_inline_data_size_valid(iomap));
> > >
> > >       flush_dcache_page(page);
> > >       addr = kmap_atomic(page);
> > > -     memcpy(iomap->inline_data + pos, addr + pos, copied);
> > > +     memcpy(iomap_inline_data(iomap, pos), addr + pos, copied);
> > >       kunmap_atomic(addr);
> > >
> > >       mark_inode_dirty(inode);
> >
> > Only tangentially related ... why do we memcpy the data into the tail
> > at write_end() time instead of at writepage() time?  I see there's a
> > workaround for that in gfs2's page_mkwrite():
> >
> >         if (gfs2_is_stuffed(ip)) {
> >                 err = gfs2_unstuff_dinode(ip);
> >
> > (an mmap store cannot change the size of the file, so this would be
> > unnecessary)
> 
> Not sure if an additional __set_page_dirty_nobuffers is needed in that
> case, but doing the writeback at writepage time should work just as
> well. It's just that gfs2 did it at write time historically. The
> un-inlining in gfs2_page_mkwrite() could probably also be removed.
> 
> I can give this a try, but I'll unfortunately be AFK for the next
> couple of days.

I tend to leave it as another new story and can be resolved with
another patch to improve it (or I will stuck in this, I need to do
my own development stuff instead of spinning with this iomap patch
since I can see this already work well for gfs2 and erofs), I will
update the patch Andreas posted with Christoph's comments.

Thanks,
Gao Xiang