> On Jun 21, 2019, at 9:30 AM, Song Liu <songliubraving@xxxxxx> wrote: > > > >> On Jun 21, 2019, at 6:45 AM, Song Liu <songliubraving@xxxxxx> wrote: >> >> >> >>> On Jun 21, 2019, at 6:36 AM, Kirill A. Shutemov <kirill@xxxxxxxxxxxxx> 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 <kirill@xxxxxxxxxxxxx> 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 <lkp@xxxxxxxxx> >>>>>> Signed-off-by: Song Liu <songliubraving@xxxxxx> >>>>>> --- >>>>>> 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
