linux-kernel - Re: [PATCH] PM / Hibernate: allow hibernation with PAGE_POISONING

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Message-ID: <20160912113238.GA30927@amd>
Date:   Mon, 12 Sep 2016 13:32:38 +0200
From:   Pavel Machek <pavel@....cz>
To:     Anisse Astier <anisse@...ier.eu>
Cc:     linux-mm@...ck.org, linux-pm@...r.kernel.org,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Laura Abbott <labbott@...oraproject.org>,
        Mel Gorman <mgorman@...e.de>,
        "Rafael J . Wysocki" <rjw@...ysocki.net>,
        Alan Cox <gnomes@...rguk.ukuu.org.uk>,
        Andi Kleen <andi@...stfloor.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Brad Spengler <spender@...ecurity.net>,
        Dave Hansen <dave.hansen@...el.com>,
        David Rientjes <rientjes@...gle.com>,
        Jianyu Zhan <nasa4836@...il.com>,
        Kees Cook <keescook@...omium.org>,
        Len Brown <len.brown@...el.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Mathias Krause <minipli@...glemail.com>,
        Michal Hocko <mhocko@...e.com>,
        PaX Team <pageexec@...email.hu>,
        Peter Zijlstra <peterz@...radead.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Yves-Alexis Perez <corsac@...ian.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] PM / Hibernate: allow hibernation with
 PAGE_POISONING_ZERO

On Fri 2016-09-09 10:43:32, Anisse Astier wrote:
> PAGE_POISONING_ZERO disables zeroing new pages on alloc, they are
> poisoned (zeroed) as they become available.
> In the hibernate use case, free pages will appear in the system without
> being cleared, left there by the loading kernel.
> 
> This patch will make sure free pages are cleared on resume when
> PAGE_POISONING_ZERO is enabled. We free the pages just after resume
> because we can't do it later: going through any device resume code might
> allocate some memory and invalidate the free pages bitmap.
> 
> Thus we don't need to disable hibernation when PAGE_POISONING_ZERO is
> enabled.
> 
> Signed-off-by: Anisse Astier <anisse@...ier.eu>
> Cc: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> Cc: Laura Abbott <labbott@...oraproject.org>
> Cc: Mel Gorman <mgorman@...e.de>
> Cc: Rafael J. Wysocki <rjw@...ysocki.net>

Looks reasonable to me.

Acked-by: Pavel Machek <pavel@....cz>

Actually.... this takes basically zero time come. Do we want to do it
unconditionally?

(Yes, it is free memory, but for sake of debugging, I guess zeros are
preffered to random content that changed during hibernation.)

(But that does not change the Ack.)

Best regards,
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html