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

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Date:   Mon, 8 Mar 2021 03:38:21 +0000
From:   "ruansy.fnst@...itsu.com" <ruansy.fnst@...itsu.com>
To:     Dan Williams <dan.j.williams@...el.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 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.

> 
> Although memory_failure() is inefficient for large range failures, I'm
> not seeing a better option, so I'm going to test calling
> memory_failure() over a large range whenever an in-use dax-device is
> hot-removed.
> 

I did not test this for large range failure yet...  I am not sure if it works
fine. But because of the complex tracking method, I think it would be more
inefficient in this case than before.


--
Thanks,
Ruan Shiyang.