Re: [PATCH] mm/migration: Add trace events for THP migrations

[Naoya Horiguchi <naoya.horiguchi@linux.dev>]

On Tue, Jan 11, 2022 at 10:31:21AM +0530, Anshuman Khandual wrote:
> 
> 
> On 1/11/22 7:28 AM, Naoya Horiguchi wrote:
> > Hi Anshuman,
> > 
> > On Fri, Jan 07, 2022 at 10:29:35AM +0530, Anshuman Khandual wrote:
> >> This adds two trace events for PMD based THP migration without split. These
> >> events closely follow the implementation details like setting and removing
> >> of PMD migration entries, which are essential operations for THP migration.
> > 
> > I often want to check which individual pages are migrated to which places
> > (or not migrated) for testing, so these new tracepoints could help me.
> > Maybe these can be much greater if they can handle other types of page
> > migration for raw pages and hugetlb pages.  Is it hard to cover all such
> > page migration events?
> 
> Are you suggesting to cover all migration entry transitions for normal
> and HugeTLB pages as well ?

Yes if you like the idea. I think that some events listed below can be grouped
into one tracepoint event with showing args like pgsize or read/write flags
(or implementation detail is up to you).

> 
> migrate_pages()
> 	unmap_and_move_huge_page()
> 		try_to_migrate()
> 			make_writable_migration_entry() <---
> 			make_readable_migration_entry() <---
> 		remove_migration_ptes() <---
> 	unmap_and_move()
> 		__unmap_and_move()
> 			try_to_migrate()
> 				make_writable_migration_entry() <---
> 				make_readable_migration_entry() <---
> 			remove_migration_ptes() <---

Thanks,
Naoya Horiguchi