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

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Message-ID: <YcXdvnLC5SyiSZTc@casper.infradead.org>
Date:   Fri, 24 Dec 2021 14:48:30 +0000
From:   Matthew Wilcox <willy@...radead.org>
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 <n-horiguchi@...jp.nec.com>,
        John Hubbard <jhubbard@...dia.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC] mm/migration: Add trace events for THP migrations

On Fri, Dec 24, 2021 at 12:16:38PM +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.

Why are you printing the address of a struct page?  What useful
information does this supply?  Same question for the struct mm.
And the pmdp, for that matter.

You haven't said _why_ you want these tracepoints.  So it's impossible
to suggest what you _should_ be doing, because what you _are_ doing
is obviously wrong.

> +	TP_printk("mm=%p, address=%lx, pmdp=%p, page=%p pmdval=%lx",
> +		__entry->mm,
> +		__entry->address,
> +		__entry->pmdp,
> +		__entry->page,
> +		__entry->pmdval)
> +);