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[140.211.169.12]) by mx.google.com with ESMTPS id j66si5990125pfb.182.2019.01.31.14.14.52 for (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 31 Jan 2019 14:14:53 -0800 (PST) Received-SPF: pass (google.com: domain of akpm@linux-foundation.org designates 140.211.169.12 as permitted sender) client-ip=140.211.169.12; Authentication-Results: mx.google.com; spf=pass (google.com: domain of akpm@linux-foundation.org designates 140.211.169.12 as permitted sender) smtp.mailfrom=akpm@linux-foundation.org Received: from localhost.localdomain (c-73-223-200-170.hsd1.ca.comcast.net [73.223.200.170]) by mail.linuxfoundation.org (Postfix) with ESMTPSA id 75F3EE48; Thu, 31 Jan 2019 22:14:52 +0000 (UTC) Date: Thu, 31 Jan 2019 14:14:51 -0800 From: Andrew Morton To: Dan Williams Cc: Michal Hocko , Dave Hansen , Kees Cook , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v9 3/3] mm: Maintain randomization of page free lists Message-Id: <20190131141451.f60cdc434f97a31e3136ade4@linux-foundation.org> In-Reply-To: <154882454628.1338686.46582179767934746.stgit@dwillia2-desk3.amr.corp.intel.com> References: <154882453052.1338686.16411162273671426494.stgit@dwillia2-desk3.amr.corp.intel.com> <154882454628.1338686.46582179767934746.stgit@dwillia2-desk3.amr.corp.intel.com> X-Mailer: Sylpheed 3.5.1 (GTK+ 2.24.31; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue, 29 Jan 2019 21:02:26 -0800 Dan Williams wrote: > When freeing a page with an order >= shuffle_page_order randomly select > the front or back of the list for insertion. > > While the mm tries to defragment physical pages into huge pages this can > tend to make the page allocator more predictable over time. Inject the > front-back randomness to preserve the initial randomness established by > shuffle_free_memory() when the kernel was booted. > > The overhead of this manipulation is constrained by only being applied > for MAX_ORDER sized pages by default. > > > ... > > --- a/include/linux/mmzone.h > +++ b/include/linux/mmzone.h > @@ -98,6 +98,10 @@ extern int page_group_by_mobility_disabled; > struct free_area { > struct list_head free_list[MIGRATE_TYPES]; > unsigned long nr_free; > +#ifdef CONFIG_SHUFFLE_PAGE_ALLOCATOR > + u64 rand; > + u8 rand_bits; > +#endif > }; > > /* Used for pages not on another list */ > @@ -116,6 +120,14 @@ static inline void add_to_free_area_tail(struct page *page, struct free_area *ar > area->nr_free++; > } > > +#ifdef CONFIG_SHUFFLE_PAGE_ALLOCATOR > +/* Used to preserve page allocation order entropy */ > +void add_to_free_area_random(struct page *page, struct free_area *area, > + int migratetype); > +#else > +#define add_to_free_area_random add_to_free_area A static inline would be nicer. > +#endif > + > /* Used for pages which are on another list */ > static inline void move_to_free_area(struct page *page, struct free_area *area, > int migratetype) > > ... > > --- a/mm/shuffle.c > +++ b/mm/shuffle.c > @@ -186,3 +186,19 @@ void __meminit __shuffle_free_memory(pg_data_t *pgdat) > for (z = pgdat->node_zones; z < pgdat->node_zones + MAX_NR_ZONES; z++) > shuffle_zone(z); > } > + > +void add_to_free_area_random(struct page *page, struct free_area *area, > + int migratetype) > +{ > + if (area->rand_bits == 0) { > + area->rand_bits = 64; > + area->rand = get_random_u64(); > + } > + > + if (area->rand & 1) > + add_to_free_area(page, area, migratetype); > + else > + add_to_free_area_tail(page, area, migratetype); > + area->rand_bits--; > + area->rand >>= 1; > +} Well that's nice and simple.