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

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Date:   Tue, 11 Jan 2022 10:31:21 +0530
From:   Anshuman Khandual <anshuman.khandual@....com>
To:     Naoya Horiguchi <naoya.horiguchi@...ux.dev>
Cc:     linux-mm@...ck.org, Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Zi Yan <ziy@...dia.com>,
        Naoya Horiguchi <naoya.horiguchi@....com>,
        John Hubbard <jhubbard@...dia.com>,
        Matthew Wilcox <willy@...radead.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/migration: Add trace events for THP migrations



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 ?

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
>