On 8/16/23 2:45 PM, Michał Mirosław wrote:
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.
I'll remove it and add a short 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;
This condition is to cater for the case when for loop doesn't execute at all because the address range was zero. In that case start == end. So p.arg.start or p.arg.end both would work fine. I'll add p.arg.end in accordance to above loop.
Other than that, the patch looks complete now. Thanks for all your work!
I'll send the next revision.
Best Regards Michał Mirosław