On Wed, Nov 28, 2018 at 03:00:52PM -0800, Andrew Morton wrote:
>On Wed, 28 Nov 2018 16:36:34 +0800 Wei Yang <richard.weiyang@xxxxxxxxx> wrote:
>
>> When DEFERRED_STRUCT_PAGE_INIT is set, page struct will not be
>> initialized all at boot up. Some of them is postponed to defer stage.
>> While the global variable highest_memmap_pfn is still set to the highest
>> pfn at boot up, even some of them are not initialized.
>>
>> This patch adjust this behavior by update highest_memmap_pfn with the
>> exact pfn during each iteration. Since each node has a defer thread,
>> introduce a spin lock to protect it.
>>
>
>Does this solve any known problems? If so then I'm suspecting that
>those problems go deeper than this.
Corrently I don't see any problem.
>
>Why use a spinlock rather than an atomic_long_t?
Sorry for my shortage in knowledge. I am not sure how to compare and
change a value atomicly. cmpxchg just could compare the exact value.
>
>Perhaps this check should instead be built into pfn_valid()?
I think the original commit 22b31eec63e5 ('badpage: vm_normal_page use
print_bad_pte') introduce highest_memmap_pfn to make pfn_valid()
cheaper.
Some definition of pfn_valid() is :
#define pfn_valid(pfn) ((pfn) < max_pfn)
Which doesn't care about the exact presented or memmap-ed page.
I am not for sure all pfn_valid() could leverage this. One thing for
sure is there are only two users of highest_memmap_pfn
* vm_normal_page_pmd
* _vm_normal_page
--
Wei Yang
Help you, Help me
