On Wed, Aug 16, 2023 at 11:59:21AM +0500, Muhammad Usama Anjum wrote:
The PAGEMAP_SCAN IOCTL on the pagemap file can be used to get or optionally clear the info about page table entries.
[...]
--- a/fs/proc/task_mmu.c +++ b/fs/proc/task_mmu.c
[...]
+static long do_pagemap_scan(struct mm_struct *mm, unsigned long uarg) +{
[...]
- for (walk_start = p.arg.start; walk_start < p.arg.end;
walk_start = p.arg.walk_end) {long n_out;if (fatal_signal_pending(current)) {ret = -EINTR;break;}ret = mmap_read_lock_killable(mm);if (ret)break;ret = walk_page_range(mm, walk_start, p.arg.end,&pagemap_scan_ops, &p);mmap_read_unlock(mm);n_out = pagemap_scan_flush_buffer(&p);if (n_out < 0)ret = n_out;elsen_ranges_out += n_out;p.arg.walk_end = p.walk_end_addr ? p.walk_end_addr : p.arg.end;
I think p.walk_end_addr can be removed and replaced by `p.arg.walk_end` directly in the walk functions. If we don't set walk_end_addr we'll also return 0 so the check below will match. Might be good to add this as a comment.
if (ret != -ENOSPC)break;if (p.arg.vec_len == 0 || p.found_pages == p.arg.max_pages)break;- }
- /* ENOSPC signifies early stop (buffer full) from the walk. */
- if (!ret || ret == -ENOSPC)
ret = n_ranges_out;- p.arg.walk_end = p.arg.walk_end ? p.arg.walk_end : walk_start;
When the walk is finished, with ret == 0, the walk_start will point to the beginning, not the end of the range. So:
if (!walk_end) walk_end = p.arg.end;
Other than that, the patch looks complete now. Thanks for all your work!
Best Regards Michał Mirosław