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

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Date:   Thu, 2 Jun 2022 17:42:13 +0800
From:   Shiyang Ruan <ruansy.fnst@...itsu.com>
To:     Dan Williams <dan.j.williams@...el.com>
CC:     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>,
        "Darrick J. Wong" <djwong@...nel.org>,
        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

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@...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.
> 
>