Re: [PATCH 2/2] uprobe: collapse THP pmd after removing all uprobes

[Song Liu <songliubraving@fb.com>]

> On Jul 30, 2019, at 8:01 AM, Kirill A. Shutemov <kirill@shutemov.name> wrote:
> 
> On Sun, Jul 28, 2019 at 10:43:35PM -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 by calling khugepaged_add_pte_mapped_thp().
>> 
>> Signed-off-by: Song Liu <songliubraving@fb.com>
>> ---
>> kernel/events/uprobes.c | 9 +++++++++
>> 1 file changed, 9 insertions(+)
>> 
>> diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
>> index 58ab7fc7272a..cc53789fefc6 100644
>> --- a/kernel/events/uprobes.c
>> +++ b/kernel/events/uprobes.c
>> @@ -26,6 +26,7 @@
>> #include <linux/percpu-rwsem.h>
>> #include <linux/task_work.h>
>> #include <linux/shmem_fs.h>
>> +#include <linux/khugepaged.h>
>> 
>> #include <linux/uprobes.h>
>> 
>> @@ -470,6 +471,7 @@ int uprobe_write_opcode(struct arch_uprobe *auprobe, struct mm_struct *mm,
>> 	struct page *old_page, *new_page;
>> 	struct vm_area_struct *vma;
>> 	int ret, is_register, ref_ctr_updated = 0;
>> +	bool orig_page_huge = false;
>> 
>> 	is_register = is_swbp_insn(&opcode);
>> 	uprobe = container_of(auprobe, struct uprobe, arch);
>> @@ -525,6 +527,9 @@ int uprobe_write_opcode(struct arch_uprobe *auprobe, struct mm_struct *mm,
>> 
>> 				/* dec_mm_counter for old_page */
>> 				dec_mm_counter(mm, MM_ANONPAGES);
>> +
>> +				if (PageCompound(orig_page))
>> +					orig_page_huge = true;
>> 			}
>> 			put_page(orig_page);
>> 		}
>> @@ -543,6 +548,10 @@ int uprobe_write_opcode(struct arch_uprobe *auprobe, struct mm_struct *mm,
>> 	if (ret && is_register && ref_ctr_updated)
>> 		update_ref_ctr(uprobe, mm, -1);
>> 
>> +	/* try collapse pmd for compound page */
>> +	if (!ret && orig_page_huge)
>> +		khugepaged_add_pte_mapped_thp(mm, vaddr & HPAGE_PMD_MASK);
>> +
> 
> IIUC, here you have all locks taken, so you should be able to call
> collapse_pte_mapped_thp() directly, shouldn't you?
> 

Yes, we can call it directly. I had it that way in a very early 
version. 

Let me do that in the next version. 

Thanks,
Song