[PATCH] BadRAM for 2.6.14

[PATCH] BadRAM for 2.6.14

[Max Kellermann]

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Hi Rick,

I have ported your BadRAM patch to the new kernel 2.6.14.  There were
a few tiny formal corrections due to patch conflicts; besides that, I
did not change anything.

To linux-kernel: is there a reason why this patch was never added to
Linus' tree?  It helped me save money more than once.

Max


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diff -urN linux-2.6.14-orig/Documentation/badram.txt linux-2.6.14/Documentation/badram.txt
--- linux-2.6.14-orig/Documentation/badram.txt	1970-01-01 01:00:00.000000000 +0100
+++ linux-2.6.14/Documentation/badram.txt	2005-11-09 10:06:11.401290000 +0100
@@ -0,0 +1,266 @@
+INFORMATION ON USING BAD RAM MODULES
+====================================
+
+Introduction
+	RAM is getting smaller and smaller, and as a result, also more and more
+	vulnerable. This makes the manufacturing of hardware more expensive,
+	since an excessive amount of RAM chips must be discarded on account of
+	a single cell that is wrong. Similarly, static discharge may damage a
+	RAM module forever, which is usually remedied by replacing it
+	entirely.
+
+	This is not necessary, as the BadRAM code shows: By informing the Linux
+	kernel which addresses in a RAM are damaged, the kernel simply avoids
+	ever allocating such addresses but makes all the rest available.
+
+Reasons for this feature
+	There are many reasons why this kernel feature is useful:
+	- Chip manufacture is resource intensive; waste less and sleep better
+	- It's another chance to promote Linux as "the flexible OS"
+	- Some laptops have their RAM soldered in... and then it fails!
+	- It's plain cool ;-)
+
+Running example
+	To run this project, I was given two DIMMs, 32 MB each. One, that we
+	shall use as a running example in this text, contained 512 faulty bits,
+	spread over 1/4 of the address range in a regular pattern. Some tricks
+	with a RAM tester and a few binary calculations were sufficient to
+	write these faults down in 2 longword numbers.
+
+	The kernel recognised the correct number of pages with faults and did
+	not give them out for allocation. The allocation routines could
+	therefore progress as normally, without any adaption.
+	So, I gained 30 MB of DIMM which would otherwise have been thrown
+	away. After booting the kernel, the kernel behaved exactly as it
+	always had.
+
+Initial checks
+	If you experience RAM trouble, first read /usr/src/linux/memory.txt
+	and try out the mem=4M trick to see if at least some initial parts
+	of your RAM work well. The BadRAM routines halt the kernel in panic
+	if the reserved area of memory (containing kernel stuff) contains
+	a faulty address.
+
+Running a RAM checker
+	The memory checker is not built into the kernel, to avoid delays at
+	runtime. If you experience problems that may be caused by RAM, run
+	a good RAM checker, such as
+		http://reality.sgi.com/cbrady_denver/memtest86
+	The output of a RAM checker provides addresses that went wrong. In
+	the 32 MB chip with 512 faulty bits mentioned above, the errors were
+	found in the 8MB-16MB range (the DIMM was in slot #0) at addresses
+		xxx42f4
+		xxx62f4
+		xxxc2f4
+		xxxe2f4
+	and the error was a "sticky 1 bit", a memory bit that stayed "1" no
+	matter what was written to it. The regularity of this pattern
+	suggests the death of a buffer at the output stages of a row on one of
+	the chips. I expect such regularity to be commonplace. Finding this
+	regularity currently is human effort, but it should not be hard to
+	alter a RAM checker to capture it in some sort of pattern, possibly
+	the BadRAM patterns described below.
+
+	By the way, if you manage to get hold of memtest86 version 2.3 or
+	beyond, you can configure the printing mode to produce BadRAM patterns,
+	which find out exactly what you must enter on the LILO: commandline,
+	except that you shouldn't mention the added spacing. That means that
+	you can skip the following step, which saves you a *lot* of work.
+
+	Also by the way, if your machine has the ISA memory gap in the 15M-16M
+	range unstoppable, Linux can get in trouble. One way of handling that
+	situation is by specifying the total memory size to Linux with a boot
+	parameter mem=... and then to tell it to treat the 15M-16M range as
+	faulty with an additional boot parameter, for instance:
+		mem=24M badram=0x00f00000,0xfff00000
+	if you installed 24MB of RAM in total.
+
+Capturing errors in a pattern
+	Instead of manually providing all 512 errors to the kernel, it's nicer
+	to generate a pattern. Since the regularity is based on address decoding
+	software, which generally takes certain bits into account and ignores
+	others, we shall provide a faulty address F, together with a bit mask M
+	that specifies which bits must be equal to F. In C code, an address A
+	is faulty if and only if
+		(F & M) == (A & M)
+	or alternately (closer to a hardware implementation):
+		~((F ^ A) & M)
+	In the example 32 MB chip, we had the faulty addresses in 8MB-16MB:
+		xxx42f4		....0100....
+		xxx62f4		....0110....
+		xxxc2f4		....1100....
+		xxxe2f4		....1110....
+	The second column represents the alternating hex digit in binary form.
+	Apperantly, the first and one-but last binary digit can be anything,
+	so the binary mask for that part is 0101. The mask for the part after
+	this is 0xfff, and the part before should select anything in the range
+	8MB-16MB, or 0x00800000-0x01000000; this is done with a bitmask
+	0xff80xxxx. Combining these partial masks, we get:
+		F=0x008042f4    M=0xff805fff
+	That covers everything for this DIMM; for more complicated failing
+	DIMMs, or for a combination of multiple failing DIMMs, it can be
+	necessary to set up a number of such F/M pairs.
+
+Rebooting Linux
+	Now that these patterns are known (and double-checked, the calculations
+	are highly error-prone... it would be neat to test them in the RAM
+	checker...) we simply restart Linux with these F/M pairs as a parameter.
+	If you normally boot as follows:
+	       LILO: linux
+	you should now boot with
+	       LILO: linux badram=0x008042f4,0xff805fff
+	or perhaps by mentioning more F/M pairs in an order F0,M0,F1,M1,...
+	When you provide an odd number of arguments to badram, the default mask
+	0xffffffff (only one address matched) is applied to the pattern.
+
+	Beware of the commandline length. At least up to LILO version 0.21,
+	the commandline is cut off after the 78th character; later versions
+	may go as far as the kernel goes, namely 255 characters. In no way is
+	it possible to enter more than 10 numbers to the badram boot option.
+
+	When the kernel now boots, it should not give any trouble with RAM.
+	Mind you, this is under the assumption that the kernel and its data
+	storage do not overlap an erroneous part. If this happens, and the
+	kernel does not choke on it right away, it will stop with a panic.
+	You will need to provide a RAM where the initial, say 2MB, is faultless.
+
+	Now look up your memory status with
+	       dmesg | grep ^Memory:
+	which prints a single line with information like
+		Memory: 158524k/163840k available
+			(940k kernel code,
+			412k reserved,
+			1856k data,
+			60k init,
+			0k highmem,
+			2048k BadRAM)
+	The latter entry, the badram, is 2048k to represent the loss of 2MB
+	of general purpose RAM due to the errors. Or, positively rephrased,
+	instead of throwing out 32MB as useless, you only throw out 2MB.
+
+	If the system is stable (try compiling a few kernels, and do a few
+	finds in / or so) you may add the boot parameter to /etc/lilo.conf
+	as a line to _all_ the kernels that handle this trouble with a line
+		append="badram=0x008042f4,0xff805fff"
+	after which you run "lilo".
+	Warning: Don't experiment with these settings on your only boot image.
+	If the BadRAM overlays kernel code, data, init, or other reserved
+	memory, the kernel will halt in panic. Try settings on a test boot
+	image first, and if you get a panic you should change the order of
+	your DIMMs [which may involve buying a new one just to be able to
+	change the order].
+
+	You are allowed to enter any number of BadRAM patterns in all the
+	places documented in this file. They will all apply. It is even
+	possible to mention several BadRAM patterns in a single place. The
+	completion of an odd number of arguments with the default mask is
+	done separately for each badram=... option.
+
+Kernel Customisation
+	Some people prefer to enter their badram patterns in the kernel, and
+	this is also possible. In mm/page_alloc.c there is an array of unsigned
+	long integers into which the parameters can be entered, prefixed with
+	the number of integers (twice the number of patterns). The array is
+	named badram_custom and it will be added to the BadRAM list whenever an
+	option 'badram' is provided on the commandline when booting, either
+	with or without additional patterns.
+
+	For the previous example, the code would become
+
+	static unsigned long __initdata badram_custom[] = {
+		2,	// Number of longwords that follow, as F/M pairs
+		0x008042f4L, 0xff805fffL,
+	};
+
+	Even on this place you may assume the default mask to be filled in
+	when you enter an odd number of longwords. Specify the number of
+	longwords to be 0 to avoid influence of this custom BadRAM list.
+
+BadRAM classification
+	This technique may start a lively market for "dead" RAM. It is important
+	to realise that some RAMs are more dead than others. So, instead of
+	just providing a RAM size, it is also important to know the BadRAM
+	class, which is defined as follows:
+
+		A BadRAM class N means that at most 2^N bytes have a problem,
+		and that all problems with the RAMs are persistent: They
+		are predictable and always show up.
+
+	The DIMM that serves as an example here was of class 9, since 512=2^9
+	errors were found. Higher classes are worse, "correct" RAM is of class
+	-1 (or even less, at your choice).
+	Class N also means that the bitmask for your chip (if there's just one,
+	that is) counts N bits "0" and it means that (if no faults fall in the
+	same page) an amount of 2^N*PAGESIZE memory is lost, in the example on
+	an i386 architecture that would be 2^9*4k=2MB, which accounts for the
+	initial claim of 30MB RAM gained with this DIMM.
+
+	Note that this scheme has deliberately been defined to be independent
+	of memory technology and of computer architecture.
+
+Known Bugs
+	LILO is known to cut off commandlines which are too long. For the
+	lilo-0.21 distribution, a commandline may not exceed 78 characters,
+	while actually, 255 would be possible [on i386, kernel 2.2.16].
+	LILO does _not_ report too-long commandlines, but the error will
+	show up as either a panic at boot time, stating
+		panic: BadRAM page in initial area
+	or the dmesg line starting with Memory: will mention an unpredicted
+	number of kilobytes. (Note that the latter number only includes
+	errors in accessed memory.)
+
+Future Possibilities
+	It would be possible to use even more of the faulty RAMs by employing
+	them for slabs. The smaller allocation granularity of slabs makes it
+	possible to throw out just, say, 32 bytes surrounding an error. This
+	would mean that the example DIMM only looses 16kB instead of 2MB.
+	It might even be possible to allocate the slabs in such a way that,
+	where possible, the remaining bytes in a slab structure are allocated
+	around the error, reducing the RAM loss to 0 in the optimal situation!
+
+	However, this yield is somewhat faked: It is possible to provide 512
+	pages of 32-byte slabs, but it is not certain that anyone would use
+	that many 32-byte slabs at any time.
+
+	A better solution might be to alter the page allocation for a slab to
+	have a preference for BadRAM pages, and given those a special treatment.
+	This way, the BadRAM would be spread over all the slabs, which seems
+	more likely to be a `true' pay-off. This would yield more overhead at
+	slab allocation time, but on the other hand, by the nature of slabs,
+	such allocations are made as rare as possible, so it might not matter
+	that much. I am uncertain where to go.
+
+	Many suggestions have been made to insert a RAM checker at boot time;
+	since this would leave the time to do only very meager checking, it
+	is not a reasonable option; we already have a BIOS doing that in most
+	systems!
+
+	It would be interesting to integrate this functionality with the
+	self-verifying nature of ECC RAM. These memories can even distinguish
+	between recorable and unrecoverable errors! Such memory has been
+	handled in older operating systems by `testing' once-failed memory
+	blocks for a while, by placing only (reloadable) program code in it.
+	Unfortunately, I possess no faulty ECC modules to work this out.
+
+Names and Places
+	The home page of this project is on
+		http://rick.vanrein.org/linux/badram
+	This page also links to Nico Schmoigl's experimental extensions to
+	this patch (with debugging and a few other fancy things).
+
+	In case you have experiences with the BadRAM software which differ from
+	the test reportings on that site, I hope you will mail me with that
+	new information.
+
+	The BadRAM project is an idea and implementation by
+		Rick van Rein
+		Binnenes 67
+		9407 CX Assen
+		The Netherlands
+		rick@vanrein.org
+	If you like it, a postcard would be much appreciated ;-)
+
+
+							       Enjoy,
+								-Rick.
+
diff -urN linux-2.6.14-orig/Documentation/kernel-parameters.txt linux-2.6.14/Documentation/kernel-parameters.txt
--- linux-2.6.14-orig/Documentation/kernel-parameters.txt	2005-11-09 10:12:34.013201750 +0100
+++ linux-2.6.14/Documentation/kernel-parameters.txt	2005-11-09 10:06:11.405290250 +0100
@@ -26,6 +26,7 @@
 	APIC	APIC support is enabled.
 	APM	Advanced Power Management support is enabled.
 	AX25	Appropriate AX.25 support is enabled.
+	BADRAM  Support for faulty RAM chips is enabled.
 	CD	Appropriate CD support is enabled.
 	DEVFS	devfs support is enabled.
 	DRM	Direct Rendering Management support is enabled.
@@ -271,6 +272,8 @@
 	aztcd=		[HW,CD] Aztech CD268 CDROM driver
 			Format: <io>,0x79 (?)
 
+	badram=		[BADRAM] Avoid allocating faulty RAM addresses.
+
 	baycom_epp=	[HW,AX25]
 			Format: <io>,<mode>
 
diff -urN linux-2.6.14-orig/Documentation/memory.txt linux-2.6.14/Documentation/memory.txt
--- linux-2.6.14-orig/Documentation/memory.txt	2005-08-29 01:41:01.000000000 +0200
+++ linux-2.6.14/Documentation/memory.txt	2005-11-09 10:06:11.405290250 +0100
@@ -18,6 +18,14 @@
 	   as you add more memory.  Consider exchanging your 
            motherboard.
 
+	4) A static discharge or production fault causes a RAM module
+	   to have (predictable) errors, usually meaning that certain
+	   bits cannot be set or reset. Instead of throwing away your
+	   RAM module, you may read /usr/src/linux/Documentation/badram.txt
+	   to learn how to detect, locate and circuimvent such errors
+	   in your RAM module.
+
+
 All of these problems can be addressed with the "mem=XXXM" boot option
 (where XXX is the size of RAM to use in megabytes).  
 It can also tell Linux to use less memory than is actually installed.
@@ -49,6 +57,8 @@
 	  Linux to using a very small amount of memory. Use "memmap="-option
 	  together with "mem=" on systems with PCI to avoid physical address
 	  space collisions.
+	  If this helps, read Documentation/badram.txt to learn how to
+	  find and circumvent memory errors.
 
 
 Other tricks:
diff -urN linux-2.6.14-orig/arch/i386/Kconfig linux-2.6.14/arch/i386/Kconfig
--- linux-2.6.14-orig/arch/i386/Kconfig	2005-11-09 10:12:34.153210500 +0100
+++ linux-2.6.14/arch/i386/Kconfig	2005-11-09 10:06:11.397289750 +0100
@@ -756,6 +756,23 @@
 	depends on HIGHMEM64G
 	default y
 
+config BADRAM
+	bool "Work around bad spots in RAM"
+	default y
+	help
+	  This small kernel extension makes it possible to use memory chips
+	  which are not entirely correct. It works by never allocating the
+	  places that are wrong. Those places are specified with the badram
+	  boot option to LILO. Read Documentation/badram.txt and/or visit
+	  http://home.zonnet.nl/vanrein/badram for information.
+
+	  This option co-operates well with a second boot option from LILO
+	  that starts memtest86, which is able to automatically produce the
+	  patterns for the commandline in case of memory trouble.
+
+	  It is safe to say 'Y' here, and it is advised because there is no
+	  performance impact.
+
 # Common NUMA Features
 config NUMA
 	bool "Numa Memory Allocation and Scheduler Support"
diff -urN linux-2.6.14-orig/arch/i386/defconfig linux-2.6.14/arch/i386/defconfig
--- linux-2.6.14-orig/arch/i386/defconfig	2005-11-09 10:12:34.157210750 +0100
+++ linux-2.6.14/arch/i386/defconfig	2005-11-09 10:06:11.393289500 +0100
@@ -114,6 +114,7 @@
 CONFIG_NOHIGHMEM=y
 # CONFIG_HIGHMEM4G is not set
 # CONFIG_HIGHMEM64G is not set
+CONFIG_BADRAM=y
 # CONFIG_MATH_EMULATION is not set
 CONFIG_MTRR=y
 # CONFIG_EFI is not set
diff -urN linux-2.6.14-orig/arch/i386/mm/init.c linux-2.6.14/arch/i386/mm/init.c
--- linux-2.6.14-orig/arch/i386/mm/init.c	2005-11-09 10:12:34.197213250 +0100
+++ linux-2.6.14/arch/i386/mm/init.c	2005-11-09 10:10:21.776937500 +0100
@@ -266,25 +266,38 @@
 	pkmap_page_table = pte;	
 }
 
-void __init one_highpage_init(struct page *page, int pfn, int bad_ppro)
+/**
+ * @param bad  set on return to whether the page is bad RAM
+ */
+void __init one_highpage_init(struct page *page, int pfn, int bad_ppro,
+		int *bad)
 {
+	*bad = 0;
 	if (page_is_ram(pfn) && !(bad_ppro && page_kills_ppro(pfn))) {
 		ClearPageReserved(page);
 		set_page_count(page, 1);
-		__free_page(page);
+#ifdef CONFIG_BADRAM
+		if (PageBad(page))
+			*bad = 1;
+		else
+#endif
+			__free_page(page);
 		totalhigh_pages++;
 	} else
 		SetPageReserved(page);
 }
 
 #ifdef CONFIG_NUMA
-extern void set_highmem_pages_init(int);
+extern void set_highmem_pages_init(int, *int);
 #else
-static void __init set_highmem_pages_init(int bad_ppro)
+static void __init set_highmem_pages_init(int bad_ppro, int *pbad)
 {
 	int pfn;
-	for (pfn = highstart_pfn; pfn < highend_pfn; pfn++)
-		one_highpage_init(pfn_to_page(pfn), pfn, bad_ppro);
+	int bad;
+	for (pfn = highstart_pfn; pfn < highend_pfn; pfn++) {
+		one_highpage_init(pfn_to_page(pfn), pfn, bad_ppro, &bad);
+		if (bad) *pbad++;
+	}
 	totalram_pages += totalhigh_pages;
 }
 #endif /* CONFIG_FLATMEM */
@@ -292,7 +305,7 @@
 #else
 #define kmap_init() do { } while (0)
 #define permanent_kmaps_init(pgd_base) do { } while (0)
-#define set_highmem_pages_init(bad_ppro) do { } while (0)
+#define set_highmem_pages_init(bad_ppro, pbad) do { } while (0)
 #endif /* CONFIG_HIGHMEM */
 
 unsigned long long __PAGE_KERNEL = _PAGE_KERNEL;
@@ -537,7 +550,7 @@
 void __init mem_init(void)
 {
 	extern int ppro_with_ram_bug(void);
-	int codesize, reservedpages, datasize, initsize;
+	int codesize, reservedpages, badpages, datasize, initsize;
 	int tmp;
 	int bad_ppro;
 
@@ -570,14 +583,20 @@
 	totalram_pages += free_all_bootmem();
 
 	reservedpages = 0;
-	for (tmp = 0; tmp < max_low_pfn; tmp++)
+	badpages = 0;
+	for (tmp = 0; tmp < max_low_pfn; tmp++) {
 		/*
-		 * Only count reserved RAM pages
+		 * Only count reserved and bad RAM pages
 		 */
 		if (page_is_ram(tmp) && PageReserved(pfn_to_page(tmp)))
 			reservedpages++;
+#ifdef CONFIG_BADRAM
+		if (page_is_ram(tmp) && PageBad(pfn_to_page(tmp)))
+			badpages++;
+#endif
+	}
 
-	set_highmem_pages_init(bad_ppro);
+	set_highmem_pages_init(bad_ppro, &badpages);
 
 	codesize =  (unsigned long) &_etext - (unsigned long) &_text;
 	datasize =  (unsigned long) &_edata - (unsigned long) &_etext;
@@ -587,6 +606,18 @@
 	kclist_add(&kcore_vmalloc, (void *)VMALLOC_START, 
 		   VMALLOC_END-VMALLOC_START);
 
+#ifdef CONFIG_BADRAM
+	printk(KERN_INFO "Memory: %luk/%luk available (%dk kernel code, %dk reserved, %dk data, %dk init, %ldk highmem, %dk BadRAM)\n",
+		(unsigned long) nr_free_pages() << (PAGE_SHIFT-10),
+		num_physpages << (PAGE_SHIFT-10),
+		codesize >> 10,
+		reservedpages << (PAGE_SHIFT-10),
+		datasize >> 10,
+		initsize >> 10,
+		(unsigned long) (totalhigh_pages << (PAGE_SHIFT-10)),
+		badpages << (PAGE_SHIFT-10)
+	       );
+#else
 	printk(KERN_INFO "Memory: %luk/%luk available (%dk kernel code, %dk reserved, %dk data, %dk init, %ldk highmem)\n",
 		(unsigned long) nr_free_pages() << (PAGE_SHIFT-10),
 		num_physpages << (PAGE_SHIFT-10),
@@ -596,6 +627,7 @@
 		initsize >> 10,
 		(unsigned long) (totalhigh_pages << (PAGE_SHIFT-10))
 	       );
+#endif
 
 #ifdef CONFIG_X86_PAE
 	if (!cpu_has_pae)
diff -urN linux-2.6.14-orig/arch/i386/mm/pgtable.c linux-2.6.14/arch/i386/mm/pgtable.c
--- linux-2.6.14-orig/arch/i386/mm/pgtable.c	2005-11-09 10:12:34.197213250 +0100
+++ linux-2.6.14/arch/i386/mm/pgtable.c	2005-11-09 10:10:56.363099000 +0100
@@ -24,7 +24,7 @@
 
 void show_mem(void)
 {
-	int total = 0, reserved = 0;
+	int total = 0, reserved = 0, badram = 0;
 	int shared = 0, cached = 0;
 	int highmem = 0;
 	struct page *page;
@@ -43,6 +43,10 @@
 				highmem++;
 			if (PageReserved(page))
 				reserved++;
+#ifdef CONFIG_BADRAM
+			else if (PageBad(page))
+				badram++;
+#endif
 			else if (PageSwapCache(page))
 				cached++;
 			else if (page_count(page))
@@ -52,6 +56,9 @@
 	printk(KERN_INFO "%d pages of RAM\n", total);
 	printk(KERN_INFO "%d pages of HIGHMEM\n", highmem);
 	printk(KERN_INFO "%d reserved pages\n", reserved);
+#ifdef CONFIG_BADRAM
+	printk(KERN_INFO "%d pages of BadRAM\n",badram);
+#endif
 	printk(KERN_INFO "%d pages shared\n", shared);
 	printk(KERN_INFO "%d pages swap cached\n", cached);
 
diff -urN linux-2.6.14-orig/include/asm-i386/page.h linux-2.6.14/include/asm-i386/page.h
--- linux-2.6.14-orig/include/asm-i386/page.h	2005-11-09 10:12:37.029390250 +0100
+++ linux-2.6.14/include/asm-i386/page.h	2005-11-09 10:06:11.409290500 +0100
@@ -131,6 +131,7 @@
 #define pfn_valid(pfn)		((pfn) < max_mapnr)
 #endif /* CONFIG_FLATMEM */
 #define virt_to_page(kaddr)	pfn_to_page(__pa(kaddr) >> PAGE_SHIFT)
+#define phys_to_page(x)		(mem_map + ((unsigned long)(x) >> PAGE_SHIFT))
 
 #define virt_addr_valid(kaddr)	pfn_valid(__pa(kaddr) >> PAGE_SHIFT)
 
diff -urN linux-2.6.14-orig/include/linux/page-flags.h linux-2.6.14/include/linux/page-flags.h
--- linux-2.6.14-orig/include/linux/page-flags.h	2005-11-09 10:12:37.309407750 +0100
+++ linux-2.6.14/include/linux/page-flags.h	2005-11-09 10:11:28.181087500 +0100
@@ -75,6 +75,7 @@
 #define PG_reclaim		17	/* To be reclaimed asap */
 #define PG_nosave_free		18	/* Free, should not be written */
 #define PG_uncached		19	/* Page has been mapped as uncached */
+#define PG_badram		21      /* BadRam page */
 
 /*
  * Global page accounting.  One instance per CPU.  Only unsigned longs are
@@ -162,6 +163,10 @@
 		__mod_page_state(offset, (delta));				\
 	} while (0)
 
+#define PageBad(page)		test_bit(PG_badram, &(page)->flags)
+#define PageSetBad(page)	set_bit(PG_badram, &(page)->flags)
+#define PageTestandSetBad(page)	test_and_set_bit(PG_badram, &(page)->flags)
+
 /*
  * Manipulation of page state flags
  */
diff -urN linux-2.6.14-orig/mm/bootmem.c linux-2.6.14/mm/bootmem.c
--- linux-2.6.14-orig/mm/bootmem.c	2005-11-09 10:12:37.469417750 +0100
+++ linux-2.6.14/mm/bootmem.c	2005-11-09 10:06:11.413290750 +0100
@@ -286,10 +286,12 @@
 	pfn = bdata->node_boot_start >> PAGE_SHIFT;
 	idx = bdata->node_low_pfn - (bdata->node_boot_start >> PAGE_SHIFT);
 	map = bdata->node_bootmem_map;
+#ifndef CONFIG_BADRAM /* no idea if this is really needed */
 	/* Check physaddr is O(LOG2(BITS_PER_LONG)) page aligned */
 	if (bdata->node_boot_start == 0 ||
 	    ffs(bdata->node_boot_start) - PAGE_SHIFT > ffs(BITS_PER_LONG))
 		gofast = 1;
+#endif
 	for (i = 0; i < idx; ) {
 		unsigned long v = ~map[i / BITS_PER_LONG];
 
@@ -317,8 +319,13 @@
 				if (v & m) {
 					count++;
 					__ClearPageReserved(page);
-					set_page_refs(page, 0);
-					__free_page(page);
+#ifdef CONFIG_BADRAM
+					if (!PageBad(page))
+#endif
+					{
+						set_page_count(page, 1);
+						__free_page(page);
+					}
 				}
 			}
 		} else {
@@ -337,8 +344,13 @@
 	for (i = 0; i < ((bdata->node_low_pfn-(bdata->node_boot_start >> PAGE_SHIFT))/8 + PAGE_SIZE-1)/PAGE_SIZE; i++,page++) {
 		count++;
 		__ClearPageReserved(page);
-		set_page_count(page, 1);
-		__free_page(page);
+#ifdef CONFIG_BADRAM
+		if (!PageBad(page))
+#endif
+		{
+			set_page_count(page, 1);
+			__free_page(page);
+		}
 	}
 	total += count;
 	bdata->node_bootmem_map = NULL;
diff -urN linux-2.6.14-orig/mm/page_alloc.c linux-2.6.14/mm/page_alloc.c
--- linux-2.6.14-orig/mm/page_alloc.c	2005-11-09 10:12:37.477418250 +0100
+++ linux-2.6.14/mm/page_alloc.c	2005-11-09 10:06:11.417291000 +0100
@@ -10,6 +10,7 @@
  *  Reshaped it to be a zoned allocator, Ingo Molnar, Red Hat, 1999
  *  Discontiguous memory support, Kanoj Sarcar, SGI, Nov 1999
  *  Zone balancing, Kanoj Sarcar, SGI, Jan 2000
+ *  BadRAM handling, Rick van Rein, Feb 2001
  *  Per cpu hot/cold page lists, bulk allocation, Martin J. Bligh, Sept 2002
  *          (lots of bits borrowed from Ingo Molnar & Andrew Morton)
  */
@@ -2569,3 +2570,94 @@
 
 	return table;
 }
+
+#ifdef CONFIG_BADRAM
+
+/* Given a pointed-at address and a mask, increment the page so that the
+ * mask hides the increment. Return 0 if no increment is possible.
+ */
+static int __init next_masked_address (unsigned long *addrp, unsigned long mask)
+{
+	unsigned long inc=1;
+	unsigned long newval = *addrp;
+	while (inc & mask)
+		inc += inc;
+	while (inc != 0) {
+		newval += inc;
+		newval &= ~mask;
+		newval |= ((*addrp) & mask);
+		if (newval > *addrp) {
+			*addrp = newval;
+			return 1;
+		}
+		do {
+			inc += inc;
+		} while (inc & ~mask);
+		while (inc & mask)
+			inc += inc;
+	}
+	return 0;
+}
+
+
+void __init badram_markpages (int argc, unsigned long *argv) {
+	unsigned long addr, mask;
+	while (argc-- > 0) {
+		addr = *argv++;
+		mask = (argc-- > 0) ? *argv++ : ~0L;
+		mask |= ~PAGE_MASK;	/* Optimalisation */
+		addr &= mask;		/* Normalisation */
+		do {
+			struct page *pg = phys_to_page(addr);
+			printk ("%05lx ", __pa(__va(addr)) >> PAGE_SHIFT);
+			printk ("=%05lx/%05lx ", (unsigned long)(pg-mem_map),
+					max_mapnr);
+			/* if (VALID_PAGE(pg)) {*/
+				if (PageTestandSetBad (pg)) {
+					reserve_bootmem (addr, PAGE_SIZE);
+					printk ("BAD ");
+				}
+				else printk ("BFR ");
+			/* }*/
+			/* else printk ("INV ");*/
+		} while (next_masked_address (&addr,mask));
+	}
+}
+
+
+/*********** CONFIG_BADRAM: CUSTOMISABLE SECTION STARTS HERE ******************/
+
+
+/* Enter your custom BadRAM patterns here as pairs of unsigned long integers. */
+/* For more information on these F/M pairs, refer to Documentation/badram.txt */
+
+
+static unsigned long __initdata badram_custom[] = {
+       0,      /* Number of longwords that follow, as F/M pairs */
+};
+
+
+/*********** CONFIG_BADRAM: CUSTOMISABLE SECTION ENDS HERE ********************/
+
+
+static int __init badram_setup (char *str)
+{
+	unsigned long opts[3];
+	if (!mem_map) BUG();
+	printk ("PAGE_OFFSET=0x%08lx\n", PAGE_OFFSET);
+	printk ("BadRAM option is %s\n", str);
+	if (*str++ == '=')
+		while ((str = get_options (str, 3, (int *) opts), *opts)) {
+			printk ("   --> marking 0x%08lx, 0x%08lx  [%ld]\n",
+					opts[1], opts[2], opts[0]);
+			badram_markpages (*opts, opts+1);
+			if (*opts == 1)
+				break;
+		};
+	badram_markpages (*badram_custom, badram_custom+1);
+	return 0;
+}
+
+__setup("badram", badram_setup);
+
+#endif /* CONFIG_BADRAM */

Re: BadRAM for 2.6.14

[DaMouse]

On 11/9/05, Max Kellermann <max@duempel.org> wrote:
> Hi Rick,
>
> I have ported your BadRAM patch to the new kernel 2.6.14.  There were
> a few tiny formal corrections due to patch conflicts; besides that, I
> did not change anything.
>
> To linux-kernel: is there a reason why this patch was never added to
> Linus' tree?  It helped me save money more than once.
>
> Max
>
>
>

Hey,

Didn't happen to make a x86_64 one did you? Really good job, I love
this patch so much and I think I'll look into a 64bit variant when I'm
bored in french or something.

-DaMouse

Re: BadRAM for 2.6.14

[Kalin KOZHUHAROV]

DaMouse wrote:
> On 11/9/05, Max Kellermann <max@duempel.org> wrote:
> 
>>Hi Rick,
>>
>>I have ported your BadRAM patch to the new kernel 2.6.14.  There were
>>a few tiny formal corrections due to patch conflicts; besides that, I
>>did not change anything.
>>
>>To linux-kernel: is there a reason why this patch was never added to
>>Linus' tree?  It helped me save money more than once.

Might be because memmap boot parameter (Documentation/kernel-parameters.txt) is sufficient for most
cases?

I used a machine with 1GB RAM and 3 holes of about 5MB each for almost 2 years.

> Didn't happen to make a x86_64 one did you? Really good job, I love
> this patch so much and I think I'll look into a 64bit variant when I'm
> bored in french or something.

If this get included, a 64bit version would be appreciated though.

Kalin.

-- 
|[ ~~~~~~~~~~~~~~~~~~~~~~ ]|
+-> http://ThinRope.net/ <-+
|[ ______________________ ]|

Re: [PATCH] BadRAM for 2.6.14

[Christoph Lameter]

On Wed, 9 Nov 2005, Max Kellermann wrote:

> I have ported your BadRAM patch to the new kernel 2.6.14.  There were
> a few tiny formal corrections due to patch conflicts; besides that, I
> did not change anything.
> 
> To linux-kernel: is there a reason why this patch was never added to
> Linus' tree?  It helped me save money more than once.

We would like to do something similar but would include bad RAM removal 
while  the operating system is running. This may be because single bit ECC 
failures occur (which would cause the page to migrate away and mark the 
page as bad) or a hard ECC failure (references to the page are dropped if 
possible and the page is not dirty)