linux-kernel - Re: [PATCH v3 01/11] pagemap: Introduce ->memory

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Date:   Sun, 7 Mar 2021 21:23:47 -0800
From:   Dan Williams <dan.j.williams@...el.com>
To:     "ruansy.fnst@...itsu.com" <ruansy.fnst@...itsu.com>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-xfs <linux-xfs@...r.kernel.org>,
        linux-nvdimm <linux-nvdimm@...ts.01.org>,
        Linux MM <linux-mm@...ck.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        device-mapper development <dm-devel@...hat.com>,
        "Darrick J. Wong" <darrick.wong@...cle.com>,
        david <david@...morbit.com>, Christoph Hellwig <hch@....de>,
        Alasdair Kergon <agk@...hat.com>,
        Mike Snitzer <snitzer@...hat.com>,
        Goldwyn Rodrigues <rgoldwyn@...e.de>,
        "qi.fuli@...itsu.com" <qi.fuli@...itsu.com>,
        "y-goto@...itsu.com" <y-goto@...itsu.com>
Subject: Re: [PATCH v3 01/11] pagemap: Introduce ->memory_failure()

On Sun, Mar 7, 2021 at 7:38 PM ruansy.fnst@...itsu.com
<ruansy.fnst@...itsu.com> wrote:
>
> > On Mon, Feb 8, 2021 at 2:55 AM Shiyang Ruan <ruansy.fnst@...fujitsu.com> wrote:
> > >
> > > When memory-failure occurs, we call this function which is implemented
> > > by each kind of devices.  For the fsdax case, pmem device driver
> > > implements it.  Pmem device driver will find out the block device where
> > > the error page locates in, and try to get the filesystem on this block
> > > device.  And finally call filesystem handler to deal with the error.
> > > The filesystem will try to recover the corrupted data if possiable.
> > >
> > > Signed-off-by: Shiyang Ruan <ruansy.fnst@...fujitsu.com>
> > > ---
> > >  include/linux/memremap.h | 8 ++++++++
> > >  1 file changed, 8 insertions(+)
> > >
> > > diff --git a/include/linux/memremap.h b/include/linux/memremap.h
> > > index 79c49e7f5c30..0bcf2b1e20bd 100644
> > > --- a/include/linux/memremap.h
> > > +++ b/include/linux/memremap.h
> > > @@ -87,6 +87,14 @@ struct dev_pagemap_ops {
> > >          * the page back to a CPU accessible page.
> > >          */
> > >         vm_fault_t (*migrate_to_ram)(struct vm_fault *vmf);
> > > +
> > > +       /*
> > > +        * Handle the memory failure happens on one page.  Notify the processes
> > > +        * who are using this page, and try to recover the data on this page
> > > +        * if necessary.
> > > +        */
> > > +       int (*memory_failure)(struct dev_pagemap *pgmap, unsigned long pfn,
> > > +                             int flags);
> > >  };
> >
> > After the conversation with Dave I don't see the point of this. If
> > there is a memory_failure() on a page, why not just call
> > memory_failure()? That already knows how to find the inode and the
> > filesystem can be notified from there.
>
> We want memory_failure() supports reflinked files.  In this case, we are not
> able to track multiple files from a page(this broken page) because
> page->mapping,page->index can only track one file.  Thus, I introduce this
> ->memory_failure() implemented in pmem driver, to call ->corrupted_range()
> upper level to upper level, and finally find out files who are
> using(mmapping) this page.
>

I know the motivation, but this implementation seems backwards. It's
already the case that memory_failure() looks up the address_space
associated with a mapping. From there I would expect a new 'struct
address_space_operations' op to let the fs handle the case when there
are multiple address_spaces associated with a given file.