linux-kernel - Re: [PATCH 3/3] mm, page_alloc: reduce static keys in prep_new

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Message-ID: <1d131524-6383-fb37-00e7-ba52ae6de66b@redhat.com>
Date:   Wed, 28 Oct 2020 09:38:25 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Vlastimil Babka <vbabka@...e.cz>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Alexander Potapenko <glider@...gle.com>,
        Kees Cook <keescook@...omium.org>,
        Michal Hocko <mhocko@...nel.org>,
        Mateusz Nosek <mateusznosek0@...il.com>,
        Laura Abbott <labbott@...nel.org>
Subject: Re: [PATCH 3/3] mm, page_alloc: reduce static keys in prep_new_page()

On 27.10.20 18:41, Vlastimil Babka wrote:
> On 10/27/20 2:32 PM, Vlastimil Babka wrote:
>> So my conclusion:
>> - We can remove PAGE_POISONING_NO_SANITY because it only makes sense with
>> PAGE_POISONING_ZERO, and we can use init_on_free instead
> 
> Note for this we first have to make sanity checking compatible with
> hibernation, but that should be easy as the zeroing variants already
> paved the way. The patch below will be added to the next version of
> the series:
> 
>   From 44474ee27c4f5248061ea2e5bbc2aeefc91bcdfc Mon Sep 17 00:00:00 2001
> From: Vlastimil Babka <vbabka@...e.cz>
> Date: Tue, 27 Oct 2020 18:25:17 +0100
> Subject: [PATCH] kernel/power: allow hibernation with page_poison sanity
>    checking
> 
> Page poisoning used to be incompatible with hibernation, as the state of
> poisoned pages was lost after resume, thus enabling CONFIG_HIBERNATION forces
> CONFIG_PAGE_POISONING_NO_SANITY. For the same reason, the poisoning with zeroes
> variant CONFIG_PAGE_POISONING_ZERO used to disable hibernation. The latter
> restriction was removed by commit 1ad1410f632d ("PM / Hibernate: allow
> hibernation with PAGE_POISONING_ZERO") and similarly for init_on_free by commit
> 18451f9f9e58 ("PM: hibernate: fix crashes with init_on_free=1") by making sure
> free pages are cleared after resume.
> 
> We can use the same mechanism to instead poison free pages with PAGE_POISON
> after resume. This covers both zero and 0xAA patterns. Thus we can remove the
> Kconfig restriction that disables page poison sanity checking when hibernation
> is enabled.

I haven't fully dived into the details, but the idea it sounds sane to me.


-- 
Thanks,

David / dhildenb