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

Andrew Morton
2021-11-05T20:36:09Z

From: Peter Xu <peterx@redhat.com>
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/20210917164756.8586-4-peterx@redhat.com
Signed-off-by: Peter Xu <peterx@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

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

--- 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;
}
}
_