[PATCH v3] mm: mincore: use pte_batch_bint() to batch process large folios

[Baolin Wang <baolin.wang@linux.alibaba.com>]

When I tested the mincore() syscall, I observed that it takes longer with
64K mTHP enabled on my Arm64 server. The reason is the mincore_pte_range()
still checks each PTE individually, even when the PTEs are contiguous,
which is not efficient.

Thus we can use pte_batch_hint() to get the batch number of the present
contiguous PTEs, which can improve the performance. I tested the mincore()
syscall with 1G anonymous memory populated with 64K mTHP, and observed an
obvious performance improvement:

w/o patch		w/ patch		changes
6022us			549us			+91%

Moreover, I also tested mincore() with disabling mTHP/THP, and did not
see any obvious regression for base pages.

Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>
---
Changes from v2:
- Re-calculate the max_nr, per Barry.
Changes from v1:
- Change to use pte_batch_hint() to get the batch number, per Ryan.

Note: I observed the min_t() can introduce a slight performance regression
for base pages, so I change to add a batch size check for base pages,
which can resolve the performance regression issue.
---
 mm/mincore.c | 22 +++++++++++++++++-----
 1 file changed, 17 insertions(+), 5 deletions(-)

diff --git a/mm/mincore.c b/mm/mincore.c
index 832f29f46767..42d6c9c8da86 100644
--- a/mm/mincore.c
+++ b/mm/mincore.c
@@ -21,6 +21,7 @@
 
 #include <linux/uaccess.h>
 #include "swap.h"
+#include "internal.h"
 
 static int mincore_hugetlb(pte_t *pte, unsigned long hmask, unsigned long addr,
 			unsigned long end, struct mm_walk *walk)
@@ -105,6 +106,7 @@ static int mincore_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end,
 	pte_t *ptep;
 	unsigned char *vec = walk->private;
 	int nr = (end - addr) >> PAGE_SHIFT;
+	int step, i;
 
 	ptl = pmd_trans_huge_lock(pmd, vma);
 	if (ptl) {
@@ -118,16 +120,26 @@ static int mincore_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end,
 		walk->action = ACTION_AGAIN;
 		return 0;
 	}
-	for (; addr != end; ptep++, addr += PAGE_SIZE) {
+	for (; addr != end; ptep += step, addr += step * PAGE_SIZE) {
 		pte_t pte = ptep_get(ptep);
 
+		step = 1;
 		/* We need to do cache lookup too for pte markers */
 		if (pte_none_mostly(pte))
 			__mincore_unmapped_range(addr, addr + PAGE_SIZE,
 						 vma, vec);
-		else if (pte_present(pte))
-			*vec = 1;
-		else { /* pte is a swap entry */
+		else if (pte_present(pte)) {
+			unsigned int batch = pte_batch_hint(ptep, pte);
+
+			if (batch > 1) {
+				unsigned int max_nr = (end - addr) >> PAGE_SHIFT;
+
+				step = min_t(unsigned int, batch, max_nr);
+			}
+
+			for (i = 0; i < step; i++)
+				vec[i] = 1;
+		} else { /* pte is a swap entry */
 			swp_entry_t entry = pte_to_swp_entry(pte);
 
 			if (non_swap_entry(entry)) {
@@ -146,7 +158,7 @@ static int mincore_pte_range(pmd_t *pmd, unsigned long addr, unsigned long end,
 #endif
 			}
 		}
-		vec++;
+		vec += step;
 	}
 	pte_unmap_unlock(ptep - 1, ptl);
 out:
-- 
2.43.5