"Aneesh Kumar K.V" <aneesh.ku...@linux.ibm.com> writes:
> "Oliver O'Halloran" <ooh...@gmail.com> writes:
>
>> On Sat, Jun 29, 2019 at 5:39 PM Aneesh Kumar K.V
>> <aneesh.ku...@linux.ibm.com> wrote:
>>>
>>> Allocation from altmap area can fail based on vmemmap page size used. Add
>>> kernel
>>> info message to indicate the failure. That allows the user to identify
>>> whether they
>>> are really using persistent memory reserved space for per-page metadata.
>>>
>>> The message looks like:
>>> [ 136.587212] altmap block allocation failed, falling back to system memory
>>>
>>> Signed-off-by: Aneesh Kumar K.V <aneesh.ku...@linux.ibm.com>
>>> ---
>>> arch/powerpc/mm/init_64.c | 6 +++++-
>>> 1 file changed, 5 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/arch/powerpc/mm/init_64.c b/arch/powerpc/mm/init_64.c
>>> index a4e17a979e45..57c0573650dc 100644
>>> --- a/arch/powerpc/mm/init_64.c
>>> +++ b/arch/powerpc/mm/init_64.c
>>> @@ -194,8 +194,12 @@ int __meminit vmemmap_populate(unsigned long start,
>>> unsigned long end, int node,
>>> * fail due to alignment issues when using 16MB hugepages,
>>> so
>>> * fall back to system memory if the altmap allocation fail.
>>> */
>>> - if (altmap)
>>> + if (altmap) {
>>> p = altmap_alloc_block_buf(page_size, altmap);
>>> + if (!p)
>>
>>> + pr_info("altmap block allocation failed, " \
>>> + "falling back to system memory");
>>
>> I think this is kind of misleading. If you're mapping a large amount
>> of memory you can have most of the vmemmap backing allocated from the
>> altmap and one extra block allocated from normal memory. E.g. If you
>> have 32MB of altmap space, one 16MB block will be allocated from the
>> altmap, but the 2nd 16MB block is probably unusable due to the
>> reserved pages at the start of the altmap. Maybe this should be a
>> pr_debug() so it's only printed along with the "vmemmap_populate ..."
>> message above?
>
> Will switch to pr_debug. What I really wanted was an indication of which
> pfn device failed to allocate per page meata data in the device. But
> we really don't have device details here and we don't end up calling
> this function if there is already a 16MB mapping in DRAM for this area.
>
>>
>> Also, isn't kernel style to keep printf()s, even long ones, on one line?
>
> I was not sure. It do print to kernel log in one line.
It should be one line so it's easy to grep for the error string.
cheers
