[PATCH v4 03/11] mm/gup: Applies counting method to monitor gup_pgd_range

Leonardo Bras
2019-09-27T23:40:00Z

As decribed, gup_pgd_range is a lockless pagetable walk. So, in order to
monitor against THP split/collapse with the couting method, it's necessary
to bound it with {start,end}_lockless_pgtbl_walk.

There are dummy functions, so it is not going to add any overhead on archs
that don't use this method.

Signed-off-by: Leonardo Bras <leonardo@linux.ibm.com>
---
mm/gup.c | 8 ++++++++
1 file changed, 8 insertions(+)

diff --git a/mm/gup.c b/mm/gup.c
index 98f13ab37bac..7105c829cf44 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -2325,6 +2325,7 @@ static bool gup_fast_permitted(unsigned long start, unsigned long end)
int __get_user_pages_fast(unsigned long start, int nr_pages, int write,
struct page **pages)
{
+ struct mm_struct *mm;
unsigned long len, end;
unsigned long flags;
int nr = 0;
@@ -2352,9 +2353,12 @@ int __get_user_pages_fast(unsigned long start, int nr_pages, int write,

if (IS_ENABLED(CONFIG_HAVE_FAST_GUP) &&
gup_fast_permitted(start, end)) {
+ mm = current->mm;
+ start_lockless_pgtbl_walk(mm);
local_irq_save(flags);
gup_pgd_range(start, end, write ? FOLL_WRITE : 0, pages, &nr);
local_irq_restore(flags);
+ end_lockless_pgtbl_walk(mm);
}

return nr;
@@ -2404,6 +2408,7 @@ int get_user_pages_fast(unsigned long start, int nr_pages,
unsigned int gup_flags, struct page **pages)
{
unsigned long addr, len, end;
+ struct mm_struct *mm;
int nr = 0, ret = 0;

if (WARN_ON_ONCE(gup_flags & ~(FOLL_WRITE | FOLL_LONGTERM)))
@@ -2421,9 +2426,12 @@ int get_user_pages_fast(unsigned long start, int nr_pages,

if (IS_ENABLED(CONFIG_HAVE_FAST_GUP) &&
gup_fast_permitted(start, end)) {
+ mm = current->mm;
+ start_lockless_pgtbl_walk(mm);
local_irq_disable();
gup_pgd_range(addr, end, gup_flags, pages, &nr);
local_irq_enable();
+ end_lockless_pgtbl_walk(mm);
ret = nr;
}

--
2.20.1