mm: introduce common help functions to deal with reserved/managed pages

The original goal of this patchset is to fix the bug reported by

  https://bugzilla.kernel.org/show_bug.cgi?id=53501

Now it has also been expanded to reduce common code used by memory
initializion.

This is the first part, which applies to v3.9-rc1.

It introduces following common helper functions to simplify
free_initmem() and free_initrd_mem() on different architectures:

adjust_managed_page_count():
	will be used to adjust totalram_pages, totalhigh_pages,
	zone->managed_pages when reserving/unresering a page.

__free_reserved_page():
	free a reserved page into the buddy system without adjusting
	page statistics info

free_reserved_page():
	free a reserved page into the buddy system and adjust page
	statistics info

mark_page_reserved():
	mark a page as reserved and adjust page statistics info

free_reserved_area():
	free a continous ranges of pages by calling free_reserved_page()

free_initmem_default():
	default method to free __init pages.

We have only tested these patchset on x86 platforms, and have done basic
compliation tests using cross-compilers from ftp.kernel.org.  That means
some code may not pass compilation on some architectures.  So any help to
test this patchset are welcomed!

There are several other parts still under development:
Part2: introduce free_highmem_page() to simplify freeing highmem pages
Part3: refine code to manage totalram_pages, totalhigh_pages and
	zone->managed_pages
Part4: introduce helper functions to simplify mem_init() and remove the
	global variable num_physpages.

This patch:

Code to deal with reserved/managed pages are duplicated by many
architectures, so introduce common help functions to reduce duplicated
code.  These common help functions will also be used to concentrate code
to modify totalram_pages and zone->managed_pages, which makes the code
much more clear.

Signed-off-by: Jiang Liu <jiang.liu@huawei.com>
Acked-by: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: "James E.J. Bottomley" <jejb@parisc-linux.org>
Cc: Anatolij Gustschin <agust@denx.de>
Cc: Aurelien Jacquiot <a-jacquiot@ti.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Chen Liqin <liqin.chen@sunplusct.com>
Cc: Chris Zankel <chris@zankel.net>
Cc: David Howells <dhowells@redhat.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: Eric Biederman <ebiederm@xmission.com>
Cc: Fenghua Yu <fenghua.yu@intel.com>
Cc: Guan Xuetao <gxt@mprc.pku.edu.cn>
Cc: Haavard Skinnemoen <hskinnemoen@gmail.com>
Cc: Hans-Christian Egtvedt <egtvedt@samfundet.no>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Helge Deller <deller@gmx.de>
Cc: Hirokazu Takata <takata@linux-m32r.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru>
Cc: James Hogan <james.hogan@imgtec.com>
Cc: Jeff Dike <jdike@addtoit.com>
Cc: Jiang Liu <jiang.liu@huawei.com>
Cc: Jiang Liu <liuj97@gmail.com>
Cc: Jonas Bonn <jonas@southpole.se>
Cc: Koichi Yasutake <yasutake.koichi@jp.panasonic.com>
Cc: Lennox Wu <lennox.wu@gmail.com>
Cc: Mark Salter <msalter@redhat.com>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Cc: Matt Turner <mattst88@gmail.com>
Cc: Max Filippov <jcmvbkbc@gmail.com>
Cc: Michal Simek <monstr@monstr.eu>
Cc: Mikael Starvik <starvik@axis.com>
Cc: Mike Frysinger <vapier@gentoo.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Paul Mundt <lethal@linux-sh.org>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Richard Henderson <rth@twiddle.net>
Cc: Russell King <linux@arm.linux.org.uk>
Cc: Sam Ravnborg <sam@ravnborg.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tony Luck <tony.luck@intel.com>
Cc: Vineet Gupta <vgupta@synopsys.com>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Yoshinori Sato <ysato@users.sourceforge.jp>
Cc: Zhang Yanfei <zhangyanfei@cn.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/mm.h

@@ -1295,6 +1295,54 @@ extern void free_area_init_node(int nid, unsigned long * zones_size,
 		unsigned long zone_start_pfn, unsigned long *zholes_size);
 extern void free_initmem(void);
 
+/*
+ * Free reserved pages within range [PAGE_ALIGN(start), end & PAGE_MASK)
+ * into the buddy system. The freed pages will be poisoned with pattern
+ * "poison" if it's non-zero.
+ * Return pages freed into the buddy system.
+ */
+extern unsigned long free_reserved_area(unsigned long start, unsigned long end,
+					int poison, char *s);
+
+static inline void adjust_managed_page_count(struct page *page, long count)
+{
+	totalram_pages += count;
+}
+
+/* Free the reserved page into the buddy system, so it gets managed. */
+static inline void __free_reserved_page(struct page *page)
+{
+	ClearPageReserved(page);
+	init_page_count(page);
+	__free_page(page);
+}
+
+static inline void free_reserved_page(struct page *page)
+{
+	__free_reserved_page(page);
+	adjust_managed_page_count(page, 1);
+}
+
+static inline void mark_page_reserved(struct page *page)
+{
+	SetPageReserved(page);
+	adjust_managed_page_count(page, -1);
+}
+
+/*
+ * Default method to free all the __init memory into the buddy system.
+ * The freed pages will be poisoned with pattern "poison" if it is
+ * non-zero. Return pages freed into the buddy system.
+ */
+static inline unsigned long free_initmem_default(int poison)
+{
+	extern char __init_begin[], __init_end[];
+
+	return free_reserved_area(PAGE_ALIGN((unsigned long)&__init_begin) ,
+				  ((unsigned long)&__init_end) & PAGE_MASK,
+				  poison, "unused kernel");
+}
+
 #ifdef CONFIG_HAVE_MEMBLOCK_NODE_MAP
 /*
  * With CONFIG_HAVE_MEMBLOCK_NODE_MAP set, an architecture may initialise its

mm/page_alloc.c

@@ -5121,6 +5121,26 @@ early_param("movablecore", cmdline_parse_movablecore);
 
 #endif /* CONFIG_HAVE_MEMBLOCK_NODE_MAP */
 
+unsigned long free_reserved_area(unsigned long start, unsigned long end,
+				 int poison, char *s)
+{
+	unsigned long pages, pos;
+
+	pos = start = PAGE_ALIGN(start);
+	end &= PAGE_MASK;
+	for (pages = 0; pos < end; pos += PAGE_SIZE, pages++) {
+		if (poison)
+			memset((void *)pos, poison, PAGE_SIZE);
+		free_reserved_page(virt_to_page(pos));
+	}
+
+	if (pages && s)
+		pr_info("Freeing %s memory: %ldK (%lx - %lx)\n",
+			s, pages << (PAGE_SHIFT - 10), start, end);
+
+	return pages;
+}
+
 /**
  * set_dma_reserve - set the specified number of pages reserved in the first zone
  * @new_dma_reserve: The number of pages to mark reserved