[RFC PATCH 24/31] sysctl: add an option to only print the head page virtual address.

[Zi Yan]

From: Zi Yan <ziy@xxxxxxxxxx>

It can help distinguish between PUD-mapped, PMD-mapped THPs, and
PTE-mapped THPs.

Signed-off-by: Zi Yan <ziy@xxxxxxxxxx>
---
 fs/proc/task_mmu.c |  7 +++++--
 kernel/sysctl.c    | 11 +++++++++++
 2 files changed, 16 insertions(+), 2 deletions(-)

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index ccf8ce760283..5106d5a07576 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -27,6 +27,9 @@
 
 #define SEQ_PUT_DEC(str, val) \
 		seq_put_decimal_ull_width(m, str, (val) << (PAGE_SHIFT-10), 8)
+
+int only_print_head_pfn;
+
 void task_mem(struct seq_file *m, struct mm_struct *mm)
 {
 	unsigned long text, lib, swap, anon, file, shmem;
@@ -1308,7 +1311,7 @@ static int pagemap_pmd_range(pmd_t *pmdp, unsigned long addr, unsigned long end,
 				flags |= PM_SOFT_DIRTY;
 			if (pm->show_pfn)
 				frame = pmd_pfn(pmd) +
-					((addr & ~PMD_MASK) >> PAGE_SHIFT);
+					(only_print_head_pfn?0:((addr & ~PMD_MASK) >> PAGE_SHIFT));
 		}
 #ifdef CONFIG_ARCH_ENABLE_THP_MIGRATION
 		else if (is_swap_pmd(pmd)) {
@@ -1394,7 +1397,7 @@ static int pagemap_pud_range(pud_t *pudp, unsigned long addr, unsigned long end,
 			flags |= PM_SOFT_DIRTY;
 		if (pm->show_pfn)
 			frame = pud_pfn(pud) +
-				((addr & ~PMD_MASK) >> PAGE_SHIFT);
+				(only_print_head_pfn?0:((addr & ~PUD_MASK) >> PAGE_SHIFT));
 	}
 
 	if (page && page_mapcount(page) == 1)
diff --git a/kernel/sysctl.c b/kernel/sysctl.c
index 6bf0be1af7e0..762535a2c7d1 100644
--- a/kernel/sysctl.c
+++ b/kernel/sysctl.c
@@ -122,6 +122,8 @@ extern int vma_no_repeat_defrag;
 extern int num_breakout_chunks;
 extern int defrag_size_threshold;
 
+extern int only_print_head_pfn;
+
 /* Constants used for minimum and  maximum */
 #ifdef CONFIG_LOCKUP_DETECTOR
 static int sixty = 60;
@@ -1750,6 +1752,15 @@ static struct ctl_table vm_table[] = {
 		.proc_handler	= proc_dointvec_minmax,
 		.extra1		= &zero,
 	},
+	{
+		.procname	= "only_print_head_pfn",
+		.data		= &only_print_head_pfn,
+		.maxlen		= sizeof(only_print_head_pfn),
+		.mode		= 0644,
+		.proc_handler	= proc_dointvec_minmax,
+		.extra1		= &zero,
+		.extra2		= &one,
+	},
 	{ }
 };
 
-- 
2.20.1