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

[Shiyang Ruan]

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?


--
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@xxxxxxxxxx> 
> > 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@xxxxxxxxxx> 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@xxxxxxxxx> 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@xxxxxxxxxxx 
> > > > > > ?
> > > > > >
> > > > > > 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.