On 8/5/23 2:53 AM, Andrei Vagin wrote:
> On Thu, Jul 27, 2023 at 2:37 AM Muhammad Usama Anjum
> <usama.anjum@xxxxxxxxxxxxx> wrote:
>>
>
> <snip>
>
>> +static long do_pagemap_scan(struct mm_struct *mm, unsigned long uarg)
>> +{
>> + unsigned long walk_start, walk_end;
>> + struct mmu_notifier_range range;
>> + struct pagemap_scan_private p;
>> + size_t n_ranges_out = 0;
>> + int ret;
>> +
>> + memset(&p, 0, sizeof(p));
>> + ret = pagemap_scan_get_args(&p.arg, uarg);
>> + if (ret)
>> + return ret;
>> +
>> + ret = pagemap_scan_init_bounce_buffer(&p);
>> + if (ret)
>> + return ret;
>> +
>> + /* Protection change for the range is going to happen. */
>> + if (p.arg.flags & PM_SCAN_WP_MATCHING) {
>> + mmu_notifier_range_init(&range, MMU_NOTIFY_PROTECTION_VMA, 0,
>> + mm, p.arg.start, p.arg.end);
>> + mmu_notifier_invalidate_range_start(&range);
>> + }
>> +
>> + walk_start = walk_end = p.arg.start;
>> + for (; walk_end != p.arg.end; walk_start = walk_end) {
>> + int n_out;
>> +
>> + walk_end = min_t(unsigned long,
>> + (walk_start + PAGEMAP_WALK_SIZE) & PAGEMAP_WALK_MASK,
>> + p.arg.end);
>
> This approach has performance implications. The basic program that scans
> its address space takes around 20-30 seconds, but it has just a few
> small mappings. The first optimization that comes to mind is to remove
> the PAGEMAP_WALK_SIZE limit and instead halt walk_page_range when the
> bounce buffer is full. After draining the buffer, the walk_page_range
> function can be restarted.
Yeah, I've this implemented in WIP and will be posting in next revision.
>
> The test program and perf data can be found here:
> https://gist.github.com/avagin/c5a22f3c78f8cb34281602dfe9c43d10
>
>> +
>> + ret = mmap_read_lock_killable(mm);
>> + if (ret)
>> + break;
>> + ret = walk_page_range(mm, walk_start, walk_end,
>> + &pagemap_scan_ops, &p);
>> + mmap_read_unlock(mm);
>> +
>> + n_out = pagemap_scan_flush_buffer(&p);
>> + if (n_out < 0)
>> + ret = n_out;
>> + else
>> + n_ranges_out += n_out;
>> +
>> + if (ret)
>> + break;
>> + }
>> +
>
> Thanks,
> Andrei
--
BR,
Muhammad Usama Anjum
