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

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Message-ID: <20220111065756.GA808887@u2004>
Date:   Tue, 11 Jan 2022 15:57:56 +0900
From:   Naoya Horiguchi <naoya.horiguchi@...ux.dev>
To:     Anshuman Khandual <anshuman.khandual@....com>
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 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