[PATCH] 2.4.25-rc1: Add user friendliness to highmem= option

From: Michael Frank
Date: Sat Feb 07 2004 - 06:55:51 EST

Marcelo,

Enclosed is a patch for x86 to make highmem= option easier to use.

- Automates alignment of highmem zone
- Fixes invalid highmem settings whether too small or to large
- Adds entry in kernel-parameters.txt

Highmem emulation can be used on any machine with at least 68MB RAM.

The patch does not add to bloat as it part of __init code.

Please consider applying it as it makes this option quite usable

Regards
Michael

Examples on a machine with 495MB available RAM:

highmem=1m

Warning highmem=1MB is too small and has been adjusted to: 4MB.
Warning bad highmem zone alignment 0x1f0000, highmem size will be adjusted.
Warning lowmem size adjusted for zone alignment to: 492MB.
Warning highmem size adjusted for zone alignment to: 3MB.
3MB HIGHMEM available.
492MB LOWMEM available.

highmem=300m

Warning bad highmem zone alignment 0x1f0000, highmem size will be adjusted.
Warning lowmem size adjusted for zone alignment to: 196MB.
Warning highmem size adjusted for zone alignment to: 299MB.
299MB HIGHMEM available.
196MB LOWMEM available.

highmem=450m

Warning highmem size adjusted for a minimum of 64MB lowmem to: 431MB.
431MB HIGHMEM available.
64MB LOWMEM available.

highmem=5000m

Warning highmem=5000MB is bigger than available 495MB and will be adjusted.
Warning highmem size adjusted for a minimum of 64MB lowmem to: 431MB.
431MB HIGHMEM available.
64MB LOWMEM available.

mem=70m highmem=300m

user-defined physical RAM map:
user: 0000000000000000 - 000000000009fc00 (usable)
user: 000000000009fc00 - 00000000000a0000 (reserved)
user: 00000000000f0000 - 0000000000100000 (reserved)
user: 0000000000100000 - 0000000004600000 (usable)
Warning highmem=300MB is bigger than available 70MB and will be adjusted.
Warning highmem size adjusted for a minimum of 64MB lowmem to: 6MB.
6MB HIGHMEM available.
64MB LOWMEM available.

mem=66m highmem=1m

user-defined physical RAM map:
user: 0000000000000000 - 000000000009fc00 (usable)
user: 000000000009fc00 - 00000000000a0000 (reserved)
user: 00000000000f0000 - 0000000000100000 (reserved)
user: 0000000000100000 - 0000000004200000 (usable)
Error highmem support requires at least 68MB but only 66MB are available.
0MB HIGHMEM available.
66MB LOWMEM available.

mem=68m highmem=10m

user-defined physical RAM map:
user: 0000000000000000 - 000000000009fc00 (usable)
user: 000000000009fc00 - 00000000000a0000 (reserved)
user: 00000000000f0000 - 0000000000100000 (reserved)
user: 0000000000100000 - 0000000004400000 (usable)
Warning highmem size adjusted for a minimum of 64MB lowmem to: 4MB.
4MB HIGHMEM available.
64MB LOWMEM available.

diff -uN -r -X /home/mhf/sys/dont/dontdiff linux-2.4.25-rc1-Vanilla/arch/i386/kernel/setup.c linux-2.4.25-rc1-mhf176/arch/i386/kernel/setup.c
--- linux-2.4.25-rc1-Vanilla/arch/i386/kernel/setup.c 2004-02-07 02:52:37.000000000 +0800
+++ linux-2.4.25-rc1-mhf176/arch/i386/kernel/setup.c 2004-02-07 18:53:47.000000000 +0800
@@ -861,9 +861,12 @@
disable_ioapic_setup();
#endif
/*
- * highmem=size forces highmem to be exactly 'size' bytes.
+ * highmem=size forces highmem to be at most 'size' bytes.
* This works even on boxes that have no highmem otherwise.
* This also works to reduce highmem size on bigger boxes.
+ *
+ * Note: highmem sise is adjusted downward for proper zone
+ * alignment of the highmem physical start address.
*/
else if (!memcmp(from, "highmem=", 8))
highmem_pages = memparse(from+8, &from) >> PAGE_SHIFT;
@@ -918,25 +921,31 @@
/*
* Determine low and high memory ranges:
*/
+
+#define ZONE_REQUIRED_PAGE_ALIGNMENT (1UL << (MAX_ORDER-1))
+#define ZONE_REQUIRED_PAGE_ALIGNMENT_MASK (ZONE_REQUIRED_PAGE_ALIGNMENT-1)
+#define PAGES_FOR_64MB (64*1024*1024/PAGE_SIZE)
+
static unsigned long __init find_max_low_pfn(void)
{
unsigned long max_low_pfn;

max_low_pfn = max_pfn;
+
if (max_low_pfn > MAXMEM_PFN) {
if (highmem_pages == -1)
highmem_pages = max_pfn - MAXMEM_PFN;
if (highmem_pages + MAXMEM_PFN < max_pfn)
max_pfn = MAXMEM_PFN + highmem_pages;
if (highmem_pages + MAXMEM_PFN > max_pfn) {
- printk("only %luMB highmem pages available, ignoring highmem size of %uMB.\n", pages_to_mb(max_pfn - MAXMEM_PFN), pages_to_mb(highmem_pages));
- highmem_pages = 0;
+ printk("Warning reducing highmem=%luMB to: %luMB.\n",
+ pages_to_mb(highmem_pages), pages_to_mb(max_pfn - MAXMEM_PFN));
+ highmem_pages = max_pfn - MAXMEM_PFN;
}
max_low_pfn = MAXMEM_PFN;
#ifndef CONFIG_HIGHMEM
/* Maximum memory usable is what is directly addressable */
- printk(KERN_WARNING "Warning only %ldMB will be used.\n",
- MAXMEM>>20);
+ printk(KERN_WARNING "Warning only %ldMB will be used.\n",MAXMEM>>20);
if (max_pfn > MAX_NONPAE_PFN)
printk(KERN_WARNING "Use a PAE enabled kernel.\n");
else
@@ -950,27 +959,53 @@
}
#endif /* !CONFIG_X86_PAE */
#endif /* !CONFIG_HIGHMEM */
- } else {
- if (highmem_pages == -1)
- highmem_pages = 0;
+ } else if (highmem_pages == -1)
+ highmem_pages = 0;
#if CONFIG_HIGHMEM
- if (highmem_pages >= max_pfn) {
- printk(KERN_ERR "highmem size specified (%uMB) is bigger than pages available (%luMB)!.\n", pages_to_mb(highmem_pages), pages_to_mb(max_pfn));
- highmem_pages = 0;
- }
- if (highmem_pages) {
- if (max_low_pfn-highmem_pages < 64*1024*1024/PAGE_SIZE){
- printk(KERN_ERR "highmem size %uMB results in smaller than 64MB lowmem, ignoring it.\n", pages_to_mb(highmem_pages));
- highmem_pages = 0;
- }
- max_low_pfn -= highmem_pages;
- }
+ if (!highmem_pages)
+ goto out;
+ if (max_pfn < PAGES_FOR_64MB + ZONE_REQUIRED_PAGE_ALIGNMENT * 2) {
+ printk(KERN_ERR
+ "Error highmem support requires at least %uMB but only %uMB are available.\n",
+ pages_to_mb(PAGES_FOR_64MB + ZONE_REQUIRED_PAGE_ALIGNMENT * 2),pages_to_mb(max_pfn));
+ highmem_pages = 0;
+ goto out;
+ }
+ if (highmem_pages > max_pfn) {
+ printk(KERN_WARNING
+ "Warning highmem=%uMB is bigger than available %luMB and will be adjusted.\n",
+ pages_to_mb(highmem_pages), pages_to_mb(max_pfn));
+ }
+ if (highmem_pages <= ZONE_REQUIRED_PAGE_ALIGNMENT) {
+ printk(KERN_WARNING
+ "Warning highmem=%uMB is too small and has been adjusted to: %uMB.\n",
+ pages_to_mb(highmem_pages),pages_to_mb(ZONE_REQUIRED_PAGE_ALIGNMENT * 2));
+ highmem_pages = ZONE_REQUIRED_PAGE_ALIGNMENT * 2;
+ }
+ if (max_low_pfn < highmem_pages || max_low_pfn-highmem_pages < PAGES_FOR_64MB){
+ highmem_pages = max_low_pfn - PAGES_FOR_64MB;
+ printk(KERN_WARNING
+ "Warning highmem size adjusted for a minimum of 64MB lowmem to: %uMB.\n",
+ pages_to_mb(highmem_pages));
+ }
+ max_low_pfn -= highmem_pages;
+ if (max_low_pfn & ZONE_REQUIRED_PAGE_ALIGNMENT_MASK) {
+ printk("Warning bad highmem zone alignment 0x%lx, highmem size will be adjusted.\n",(max_low_pfn & ZONE_REQUIRED_PAGE_ALIGNMENT_MASK) << PAGE_SHIFT);
+ highmem_pages -= ZONE_REQUIRED_PAGE_ALIGNMENT - (max_low_pfn & ZONE_REQUIRED_PAGE_ALIGNMENT_MASK);
+ max_low_pfn &= ~ZONE_REQUIRED_PAGE_ALIGNMENT_MASK;
+ max_low_pfn += ZONE_REQUIRED_PAGE_ALIGNMENT;
+ printk(KERN_WARNING
+ "Warning lowmem size adjusted for zone alignment to: %uMB.\n",
+ pages_to_mb(max_low_pfn));
+ printk(KERN_WARNING
+ "Warning highmem size adjusted for zone alignment to: %uMB.\n",
+ pages_to_mb(highmem_pages));
+ }
#else
- if (highmem_pages)
- printk(KERN_ERR "ignoring highmem size on non-highmem kernel!\n");
+ if (highmem_pages)
+ printk(KERN_ERR "Error highmem size on non-highmem kernel ignored\n");
#endif
- }
-
+out:
return max_low_pfn;
}

diff -uN -r -X /home/mhf/sys/dont/dontdiff linux-2.4.25-rc1-Vanilla/Documentation/kernel-parameters.txt linux-2.4.25-rc1-mhf176/Documentation/kernel-parameters.txt
--- linux-2.4.25-rc1-Vanilla/Documentation/kernel-parameters.txt 2004-02-06 17:06:14.000000000 +0800
+++ linux-2.4.25-rc1-mhf176/Documentation/kernel-parameters.txt 2004-02-07 19:10:39.000000000 +0800
@@ -241,6 +241,12 @@

hfmodem= [HW,AX25]

+ highmem=size[KMG] [IA32,KNL,BOOT] forces highmem to be at most 'size' bytes.
+ This works even on boxes with at least 68MB RAM that have no highmem
+ otherwise. This also works to reduce highmem size on bigger boxes.
+ Note: highmem is adjusted downward for proper zone alignment of the
+ highmem physical start address
+
hisax= [HW,ISDN]

i810= [HW,DRM]

-
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