[027/262] mm/smaps: fix shmem pte hole swap calculation

Commit Message

Andrew Morton Nov. 5, 2021, 8:35 p.m. UTC

From: Peter Xu <[e-mail]>
Subject: mm/smaps: fix shmem pte hole swap calculation

Patch series "mm/smaps: Fixes and optimizations on shmem swap handling".


This patch (of 3):

The shmem swap calculation on the privately writable mappings are using
wrong parameters as spotted by Vlastimil.  Fix them.  That's introduced in
commit 48131e03ca4e, when rework shmem_swap_usage to
shmem_partial_swap_usage.

Test program:

==================

void main(void)
{
    char *buffer, *p;
    int i, fd;

    fd = memfd_create("test", 0);
    assert(fd > 0);

    /* isize==2M*3, fill in pages, swap them out */
    ftruncate(fd, SIZE_2M * 3);
    buffer = mmap(NULL, SIZE_2M * 3, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
    assert(buffer);
    for (i = 0, p = buffer; i < SIZE_2M * 3 / 4096; i++) {
        *p = 1;
        p += 4096;
    }
    madvise(buffer, SIZE_2M * 3, MADV_PAGEOUT);
    munmap(buffer, SIZE_2M * 3);

    /*
     * Remap with private+writtable mappings on partial of the inode (<= 2M*3),
     * while the size must also be >= 2M*2 to make sure there's a none pmd so
     * smaps_pte_hole will be triggered.
     */
    buffer = mmap(NULL, SIZE_2M * 2, PROT_READ | PROT_WRITE, MAP_PRIVATE, fd, 0);
    printf("pid=%d, buffer=%p
", getpid(), buffer);

    /* Check /proc/$PID/smap_rollup, should see 4MB swap */
    sleep(1000000);
}
==================

Before the patch, smaps_rollup shows <4MB swap and the number will be
random depending on the alignment of the buffer of mmap() allocated. 
After this patch, it'll show 4MB.

Link: https://lkml.kernel.org/r/[e-mail]
Link: https://lkml.kernel.org/r/[e-mail]
Fixes: 48131e03ca4e ("mm, proc: reduce cost of /proc/pid/smaps for unpopulated shmem mappings")
Signed-off-by: Peter Xu <[e-mail]>
Reported-by: Vlastimil Babka <[e-mail]>
Reviewed-by: Vlastimil Babka <[e-mail]>
Cc: Andrea Arcangeli <[e-mail]>
Cc: Hugh Dickins <[e-mail]>
Cc: Matthew Wilcox <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
---

 fs/proc/task_mmu.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

Patch

--- a/fs/proc/task_mmu.c~mm-smaps-fix-shmem-pte-hole-swap-calculation
+++ a/fs/proc/task_mmu.c
@@ -478,9 +478,11 @@  static int smaps_pte_hole(unsigned long
 			  __always_unused int depth, struct mm_walk *walk)
 {
 	struct mem_size_stats *mss = walk->private;
+	struct vm_area_struct *vma = walk->vma;
 
-	mss->swap += shmem_partial_swap_usage(
-			walk->vma->vm_file->f_mapping, addr, end);
+	mss->swap += shmem_partial_swap_usage(walk->vma->vm_file->f_mapping,
+					      linear_page_index(vma, addr),
+					      linear_page_index(vma, end));
 
 	return 0;
 }