> On Jun 21, 2019, at 9:30 AM, Song Liu <[email protected]> wrote:
>
>
>
>> On Jun 21, 2019, at 6:45 AM, Song Liu <[email protected]> wrote:
>>
>>
>>
>>> On Jun 21, 2019, at 6:36 AM, Kirill A. Shutemov <[email protected]>
>>> wrote:
>>>
>>> On Fri, Jun 21, 2019 at 01:17:05PM +0000, Song Liu wrote:
>>>>
>>>>
>>>>> On Jun 21, 2019, at 5:48 AM, Kirill A. Shutemov <[email protected]>
>>>>> wrote:
>>>>>
>>>>> On Thu, Jun 13, 2019 at 10:57:47AM -0700, Song Liu wrote:
>>>>>> After all uprobes are removed from the huge page (with PTE pgtable), it
>>>>>> is possible to collapse the pmd and benefit from THP again. This patch
>>>>>> does the collapse.
>>>>>>
>>>>>> An issue on earlier version was discovered by kbuild test robot.
>>>>>>
>>>>>> Reported-by: kbuild test robot <[email protected]>
>>>>>> Signed-off-by: Song Liu <[email protected]>
>>>>>> ---
>>>>>> include/linux/huge_mm.h | 7 +++++
>>>>>> kernel/events/uprobes.c | 5 ++-
>>>>>> mm/huge_memory.c | 69 +++++++++++++++++++++++++++++++++++++++++
>>>>>
>>>>> I still sync it's duplication of khugepaged functinallity. We need to fix
>>>>> khugepaged to handle SCAN_PAGE_COMPOUND and probably refactor the code to
>>>>> be able to call for collapse of particular range if we have all locks
>>>>> taken (as we do in uprobe case).
>>>>>
>>>>
>>>> I see the point now. I misunderstood it for a while.
>>>>
>>>> If we add this to khugepaged, it will have some conflicts with my other
>>>> patchset. How about we move the functionality to khugepaged after these
>>>> two sets get in?
>>>
>>> Is the last patch of the patchset essential? I think this part can be done
>>> a bit later in a proper way, no?
>>
>> Technically, we need this patch to regroup pmd mapped page, and thus get
>> the performance benefit after the uprobe is detached.
>>
>> On the other hand, if we get the first 4 patches of the this set and the
>> other set in soonish. I will work on improving this patch right after that..
>
> Actually, it might be pretty easy. We can just call try_collapse_huge_pmd()
> in khugepaged.c (in khugepaged_scan_shmem() or khugepaged_scan_file() after
> my other set).
>
> Let me fold that in and send v5.
On a second thought, if we would have khugepaged to do collapse, we need a
dedicated bit to tell khugepaged which pmd to collapse. Otherwise, it may
accidentally collapse pmd that are split by other split_huge_pmd.
I could not think of a good solution here. In this case, we really need a
flag for this specific pmd. Flags for the compound_page or for the vma
would not work, as those could be shared by multiple pmds.
If the analysis above is correct, we probably need uprobe to specifically
call try_collapse_huge_pmd() for now.
Please share your suggestions.
Thanks!
Song
