linux-kernel - Re: [PATCHSETS] v14 fsdax-rmap + v11 fsdax-reflink

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Date:   Thu, 2 Jun 2022 10:18:09 -0700
From:   "Darrick J. Wong" <djwong@...nel.org>
To:     Shiyang Ruan <ruansy.fnst@...itsu.com>
Cc:     Dan Williams <dan.j.williams@...el.com>,
        Naoya Horiguchi <naoya.horiguchi@....com>,
        Matthew Wilcox <willy@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Christoph Hellwig <hch@...radead.org>,
        Dave Chinner <david@...morbit.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-xfs <linux-xfs@...r.kernel.org>,
        Linux NVDIMM <nvdimm@...ts.linux.dev>,
        Linux MM <linux-mm@...ck.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Jane Chu <jane.chu@...cle.com>,
        Goldwyn Rodrigues <rgoldwyn@...e.de>,
        Al Viro <viro@...iv.linux.org.uk>, linmiaohe@...wei.com
Subject: Re: [PATCHSETS] v14 fsdax-rmap + v11 fsdax-reflink

On Thu, Jun 02, 2022 at 05:42:13PM +0800, Shiyang Ruan wrote:
> Hi,
> 
> Is there any other work I should do with these two patchsets?  I think they
> are good for now.  So... since the 5.19-rc1 is coming, could the
> notify_failure() part be merged as your plan?

Hmm.  I don't see any of the patches 1-5,7-13 in current upstream, so
I'm guessing this means Andrew isn't taking it for 5.19?

--D

> 
> 
> --
> Thanks,
> Ruan.
> 
> 
> 在 2022/5/12 20:27, Shiyang Ruan 写道:
> > 
> > 
> > 在 2022/5/11 23:46, Dan Williams 写道:
> > > On Wed, May 11, 2022 at 8:21 AM Darrick J. Wong <djwong@...nel.org>
> > > wrote:
> > > > 
> > > > Oan Tue, May 10, 2022 at 10:24:28PM -0700, Andrew Morton wrote:
> > > > > On Tue, 10 May 2022 19:43:01 -0700 "Darrick J. Wong"
> > > > > <djwong@...nel.org> wrote:
> > > > > 
> > > > > > On Tue, May 10, 2022 at 07:28:53PM -0700, Andrew Morton wrote:
> > > > > > > On Tue, 10 May 2022 18:55:50 -0700 Dan Williams
> > > > > > > <dan.j.williams@...el.com> wrote:
> > > > > > > 
> > > > > > > > > It'll need to be a stable branch somewhere, but I don't think it
> > > > > > > > > really matters where al long as it's merged into the xfs for-next
> > > > > > > > > tree so it gets filesystem test coverage...
> > > > > > > > 
> > > > > > > > So how about let the notify_failure() bits go
> > > > > > > > through -mm this cycle,
> > > > > > > > if Andrew will have it, and then the reflnk work
> > > > > > > > has a clean v5.19-rc1
> > > > > > > > baseline to build from?
> > > > > > > 
> > > > > > > What are we referring to here?  I think a minimal thing would be the
> > > > > > > memremap.h and memory-failure.c changes from
> > > > > > > https://lkml.kernel.org/r/20220508143620.1775214-4-ruansy.fnst@fujitsu.com
> > > > > > > ?
> > > > > > > 
> > > > > > > Sure, I can scoot that into 5.19-rc1 if you think that's best.  It
> > > > > > > would probably be straining things to slip it into 5.19.
> > > > > > > 
> > > > > > > The use of EOPNOTSUPP is a bit suspect, btw.  It *sounds* like the
> > > > > > > right thing, but it's a networking errno.  I suppose
> > > > > > > livable with if it
> > > > > > > never escapes the kernel, but if it can get back to userspace then a
> > > > > > > user would be justified in wondering how the heck a filesystem
> > > > > > > operation generated a networking errno?
> > > > > > 
> > > > > > <shrug> most filesystems return EOPNOTSUPP rather
> > > > > > enthusiastically when
> > > > > > they don't know how to do something...
> > > > > 
> > > > > Can it propagate back to userspace?
> > > > 
> > > > AFAICT, the new code falls back to the current (mf_generic_kill_procs)
> > > > failure code if the filesystem doesn't provide a ->memory_failure
> > > > function or if it returns -EOPNOSUPP.  mf_generic_kill_procs can also
> > > > return -EOPNOTSUPP, but all the memory_failure() callers (madvise, etc.)
> > > > convert that to 0 before returning it to userspace.
> > > > 
> > > > I suppose the weirder question is going to be what happens when madvise
> > > > starts returning filesystem errors like EIO or EFSCORRUPTED when pmem
> > > > loses half its brains and even the fs can't deal with it.
> > > 
> > > Even then that notification is not in a system call context so it
> > > would still result in a SIGBUS notification not a EOPNOTSUPP return
> > > code. The only potential gap I see are what are the possible error
> > > codes that MADV_SOFT_OFFLINE might see? The man page is silent on soft
> > > offline failure codes. Shiyang, that's something to check / update if
> > > necessary.
> > 
> > According to the code around MADV_SOFT_OFFLINE, it will return -EIO when
> > the backend is NVDIMM.
> > 
> > Here is the logic:
> >   madvise_inject_error() {
> >       ...
> >       if (MADV_SOFT_OFFLINE) {
> >           ret = soft_offline_page() {
> >               ...
> >               /* Only online pages can be soft-offlined (esp., not
> > ZONE_DEVICE). */
> >               page = pfn_to_online_page(pfn);
> >               if (!page) {
> >                   put_ref_page(ref_page);
> >                   return -EIO;
> >               }
> >               ...
> >           }
> >       } else {
> >           ret = memory_failure()
> >       }
> >       return ret
> >   }
> > 
> > 
> > -- 
> > Thanks,
> > Ruan.
> > 
> > 
> 
>