From 10c848c8b4805ff026018bfb2b3dedd90e7b0cea Mon Sep 17 00:00:00 2001 From: Peter Xu Date: Fri, 5 Nov 2021 13:35:59 -0700 Subject: [PATCH] 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. This was introduced in commit 48131e03ca4e ("mm, proc: reduce cost of /proc/pid/smaps for unpopulated shmem mappings"), when shmem_swap_usage was reworked 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\n", 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/20210917164756.8586-1-peterx@redhat.com Link: https://lkml.kernel.org/r/20210917164756.8586-2-peterx@redhat.com Fixes: 48131e03ca4e ("mm, proc: reduce cost of /proc/pid/smaps for unpopulated shmem mappings") Signed-off-by: Peter Xu Reported-by: Vlastimil Babka Reviewed-by: Vlastimil Babka Cc: Andrea Arcangeli Cc: Hugh Dickins Cc: Matthew Wilcox Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- fs/proc/task_mmu.c | 6 ++++-- 1 file changed, 4 insertions(+), 2 deletions(-) diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c index cf25be3e0321..2197f669e17b 100644 --- a/fs/proc/task_mmu.c +++ b/fs/proc/task_mmu.c @@ -478,9 +478,11 @@ static int smaps_pte_hole(unsigned long addr, unsigned long end, __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; }