The patch titled
Subject: x86: mm: add missing comments for initial kernel direct mapping
has been added to the -mm tree. Its filename is
x86-mm-add-missing-comments-for-initial-kernel-direct-mapping.patch
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From: Zhang Yanfei <zhangyanfei@xxxxxxxxxxxxxx>
Subject: x86: mm: add missing comments for initial kernel direct mapping
For some reason, comments below are lost:
- comments for init_range_memory_mapping()
- comments in init_mem_mapping that is helpful for reminding people
that the pagetable is setup top-down
The comments were written by Yinghai in his patch in
https://lkml.org/lkml/2012/11/28/620
Signed-off-by: Zhang Yanfei <zhangyanfei@xxxxxxxxxxxxxx>
Signed-off-by: Yinghai Lu <yinghai@xxxxxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
Cc: Yasuaki Ishimatsu <isimatu.yasuaki@xxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
arch/x86/mm/init.c | 19 ++++++++++++++++++-
1 file changed, 18 insertions(+), 1 deletion(-)
diff -puN arch/x86/mm/init.c~x86-mm-add-missing-comments-for-initial-kernel-direct-mapping arch/x86/mm/init.c
--- a/arch/x86/mm/init.c~x86-mm-add-missing-comments-for-initial-kernel-direct-mapping
+++ a/arch/x86/mm/init.c
@@ -359,7 +359,17 @@ unsigned long __init_refok init_memory_m
}
/*
- * would have hole in the middle or ends, and only ram parts will be mapped.
+ * We need to iterate through E820 memory map and create direct mappings
+ * for only E820_RAM and E820_KERN_RESERVED regions. We cannot simply
+ * create direct mappings for all pfns from [0 to max_low_pfn) and
+ * [4GB to max_pfn) because of possible memory holes in high addresses
+ * that cannot be marked as UC by fixed/variable range MTRRs.
+ * Depending on the alignment of E820 ranges, this may possibly result
+ * in using smaller size (i.e. 4K instead of 2M or 1G) page tables.
+ *
+ * init_mem_mapping call init_range_memory_mapping with big range.
+ * That range would have hole in the middle or ends, and only ram parts
+ * will be mapped in init_range_memory_mapping.
*/
static unsigned long __init init_range_memory_mapping(
unsigned long r_start,
@@ -419,6 +429,13 @@ void __init init_mem_mapping(void)
max_pfn_mapped = 0; /* will get exact value next */
min_pfn_mapped = real_end >> PAGE_SHIFT;
last_start = start = real_end;
+
+ /*
+ * We start from the top (end of memory) and go to the bottom.
+ * The memblock_find_in_range gets us a block of RAM from the
+ * end of RAM in [min_pfn_mapped, max_pfn_mapped) as new pages
+ * for page table.
+ */
while (last_start > ISA_END_ADDRESS) {
if (last_start > step_size) {
start = round_down(last_start - 1, step_size);
_
Patches currently in -mm which might be from zhangyanfei@xxxxxxxxxxxxxx are
origin.patch
x86-mm-add-missing-comments-for-initial-kernel-direct-mapping.patch
ipvs-change-type-of-netns_ipvs-sysctl_sync_qlen_max.patch
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