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SubjectRe: [PATCHSETS] v14 fsdax-rmap + v11 fsdax-reflink
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在 2022/5/11 23:46, Dan Williams 写道:
> On Wed, May 11, 2022 at 8:21 AM Darrick J. Wong <djwong@kernel.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@kernel.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@intel.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.


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