linux-kernel - Re: [PATCH -next v2 09/19] mm: mprotect: use a folio in change_pte

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Message-ID: <ZSlekx1pYOh7ltaF@casper.infradead.org>
Date:   Fri, 13 Oct 2023 16:13:23 +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 09/19] mm: mprotect: use a folio in
 change_pte_range()

On Fri, Oct 13, 2023 at 04:55:53PM +0800, Kefeng Wang wrote:
> Use a folio in change_pte_range() to save three compound_head() calls.

Yes, but here we have a change of behaviour, which should be argued
is desirable.  Before if a partial THP was mapped, or a fs large
folio, we would do this to individual pages.  Now we're doing it to the
entire folio.  Is that desirable?  I don't have the background to argue
either way.

> @@ -157,7 +159,7 @@ static long change_pte_range(struct mmu_gather *tlb,
>  					continue;
>  				if (sysctl_numa_balancing_mode & NUMA_BALANCING_MEMORY_TIERING &&
>  				    !toptier)
> -					xchg_page_access_time(page,
> +					folio_xchg_access_time(folio,
>  						jiffies_to_msecs(jiffies));
>  			}