linux-kernel - Re: [PATCH -next v2 18/19] mm: use folio_xchg_last_cpupid() in wp_page

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Message-ID: <ZSlf6fPfuOo4QmDt@casper.infradead.org>
Date:   Fri, 13 Oct 2023 16:19:05 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     Kefeng Wang <wangkefeng.wang@...wei.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, ying.huang@...el.com,
        david@...hat.com, Zi Yan <ziy@...dia.com>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Juri Lelli <juri.lelli@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>
Subject: Re: [PATCH -next v2 18/19] mm: use folio_xchg_last_cpupid() in
 wp_page_reuse()

On Fri, Oct 13, 2023 at 04:56:02PM +0800, Kefeng Wang wrote:
> Convert to use folio_xchg_last_cpupid() in wp_page_reuse(), and remove
> page variable.

... another case where we're changing behaviour and need to argue it's
desirable.

> -	/*
> -	 * Clear the pages cpupid information as the existing
> -	 * information potentially belongs to a now completely
> -	 * unrelated process.
> -	 */
> -	if (page)
> -		page_cpupid_xchg_last(page, (1 << LAST_CPUPID_SHIFT) - 1);
> +	if (folio) {
> +		VM_BUG_ON(folio_test_anon(folio) &&
> +			  !PageAnonExclusive(vmf->page));
> +		/*
> +		 * Clear the pages cpupid information as the existing

s/pages/folio's/

> +		 * information potentially belongs to a now completely
> +		 * unrelated process.
> +		 */
> +		folio_xchg_last_cpupid(folio, (1 << LAST_CPUPID_SHIFT) - 1);
> +	}