linux-kernel - Re: [PATCH] mm: Split huge PUD on wp_huge

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Message-ID: <01362246-05e6-f57f-9f64-c8d2524e685d@redhat.com>
Date:   Tue, 2 Aug 2022 16:59:31 +0200
From:   David Hildenbrand <david@...hat.com>
To:     "Gowans, James" <jgowans@...zon.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "christian.koenig@....com" <christian.koenig@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Schönherr, Jan H. <jschoenh@...zon.de>,
        "thomas.hellstrom@...ux.intel.com" <thomas.hellstrom@...ux.intel.com>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>
Subject: Re: [PATCH] mm: Split huge PUD on wp_huge_pud fallback

On 23.06.22 07:24, Gowans, James wrote:
> Currently the implementation will split the PUD when a fallback is taken
> inside the create_huge_pud function. This isn't where it should be done:
> the splitting should be done in wp_huge_pud, just like it's done for
> PMDs. Reason being that if a callback is taken during create, there is
> no PUD yet so nothing to split, whereas if a fallback is taken when
> encountering a write protection fault there is something to split.
> 
> It looks like this was the original intention with the commit where the
> splitting was introduced, but somehow it got moved to the wrong place
> between v1 and v2 of the patch series. Rebase mistake perhaps.
> 
> Fixes: 327e9fd48972 ("mm: Split huge pages on write-notify or COW")

Right, the functions should just look like create_huge_pmd()/wp_huge_pmd().

I do wonder if there was a reason to do it differently, though ... I
can't spot any in current code.

Acked-by: David Hildenbrand <david@...hat.com>

-- 
Thanks,

David / dhildenb