linux-kernel - [PATCH 3/3] mm/smaps: Simplify shmem handling of pte holes

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Date:   Fri, 17 Sep 2021 12:47:56 -0400
From:   Peter Xu <peterx@...hat.com>
To:     linux-mm@...ck.org, linux-kernel@...r.kernel.org
Cc:     Vlastimil Babka <vbabka@...e.cz>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Hugh Dickins <hughd@...gle.com>,
        Andrea Arcangeli <aarcange@...hat.com>, peterx@...hat.com,
        Matthew Wilcox <willy@...radead.org>
Subject: [PATCH 3/3] 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.

Cc: Hugh Dickins <hughd@...gle.com>
Cc: Matthew Wilcox <willy@...radead.org>
Cc: Vlastimil Babka <vbabka@...e.cz>
Signed-off-by: Peter Xu <peterx@...hat.com>
---
 fs/proc/task_mmu.c | 22 ++++++++++++----------
 1 file changed, 12 insertions(+), 10 deletions(-)

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 2197f669e17b..ad667dbc96f5 100644
--- a/fs/proc/task_mmu.c
+++ b/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 addr, unsigned long end,
 #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, unsigned long addr,
 			}
 		} 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_area_struct *vma,
 		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_area_struct *vma,
 					!(vma->vm_flags & VM_WRITE))) {
 			mss->swap += shmem_swapped;
 		} else {
-			mss->check_shmem_swap = true;
 			ops = &smaps_shmem_walk_ops;
 		}
 	}
-- 
2.31.1