[029/262] mm/smaps: simplify shmem handling of pte holes

Commit Message

Andrew Morton Nov. 5, 2021, 8:36 p.m. UTC

From: Peter Xu <[e-mail]>
Subject: mm/smaps: simplify shmem handling of pte holes

Firstly, check_shmem_swap variable is actually not necessary, because it's
always set with pte_hole hook; checking each would work.

Meanwhile, the check within smaps_pte_entry is not easy to follow.  E.g.,
pte_none() check is not needed as "!pte_present && !is_swap_pte" is the
same.  Since at it, use the pte_hole() helper rather than dup the page
cache lookup.

Still keep the CONFIG_SHMEM part so the code can be optimized to nop for !SHMEM.

There will be a very slight functional change in smaps_pte_entry(), that
for !SHMEM we'll return early for pte_none (before checking page==NULL),
but that's even nicer.

Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: Peter Xu <[e-mail]>
Cc: Hugh Dickins <[e-mail]>
Cc: Matthew Wilcox <[e-mail]>
Cc: Vlastimil Babka <[e-mail]>
Cc: Andrea Arcangeli <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
---

 fs/proc/task_mmu.c |   22 ++++++++++++----------
 1 file changed, 12 insertions(+), 10 deletions(-)

Patch

--- a/fs/proc/task_mmu.c~mm-smaps-simplify-shmem-handling-of-pte-holes
+++ a/fs/proc/task_mmu.c
@@ -397,7 +397,6 @@  struct mem_size_stats {
 	u64 pss_shmem;
 	u64 pss_locked;
 	u64 swap_pss;
-	bool check_shmem_swap;
 };
 
 static void smaps_page_accumulate(struct mem_size_stats *mss,
@@ -490,6 +489,16 @@  static int smaps_pte_hole(unsigned long
 #define smaps_pte_hole		NULL
 #endif /* CONFIG_SHMEM */
 
+static void smaps_pte_hole_lookup(unsigned long addr, struct mm_walk *walk)
+{
+#ifdef CONFIG_SHMEM
+	if (walk->ops->pte_hole) {
+		/* depth is not used */
+		smaps_pte_hole(addr, addr + PAGE_SIZE, 0, walk);
+	}
+#endif
+}
+
 static void smaps_pte_entry(pte_t *pte, unsigned long addr,
 		struct mm_walk *walk)
 {
@@ -518,12 +527,8 @@  static void smaps_pte_entry(pte_t *pte,
 			}
 		} else if (is_pfn_swap_entry(swpent))
 			page = pfn_swap_entry_to_page(swpent);
-	} else if (unlikely(IS_ENABLED(CONFIG_SHMEM) && mss->check_shmem_swap
-							&& pte_none(*pte))) {
-		page = xa_load(&vma->vm_file->f_mapping->i_pages,
-						linear_page_index(vma, addr));
-		if (xa_is_value(page))
-			mss->swap += PAGE_SIZE;
+	} else {
+		smaps_pte_hole_lookup(addr, walk);
 		return;
 	}
 
@@ -737,8 +742,6 @@  static void smap_gather_stats(struct vm_
 		return;
 
 #ifdef CONFIG_SHMEM
-	/* In case of smaps_rollup, reset the value from previous vma */
-	mss->check_shmem_swap = false;
 	if (vma->vm_file && shmem_mapping(vma->vm_file->f_mapping)) {
 		/*
 		 * For shared or readonly shmem mappings we know that all
@@ -756,7 +759,6 @@  static void smap_gather_stats(struct vm_
 					!(vma->vm_flags & VM_WRITE))) {
 			mss->swap += shmem_swapped;
 		} else {
-			mss->check_shmem_swap = true;
 			ops = &smaps_shmem_walk_ops;
 		}
 	}