[PATCH] x86_64: Allow kernel page tables upto the end of memory

Previously they would be only allocated before the kernel text at
1MB. This limited the maximum supported memory to 128GB.
Now allow the e820 allocator to put them everywhere. Try
to put them beyond any DMA zones to avoid filling them up.
This should free some GFP_DMA memory compared to earlier kernels.

Signed-off-by: Andi Kleen <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

arch/x86_64/mm/init.c

···
 
 static void __init find_early_table_space(unsigned long end)
 {
-	unsigned long puds, pmds, tables;
+	unsigned long puds, pmds, tables, start;
 
 	puds = (end + PUD_SIZE - 1) >> PUD_SHIFT;
 	pmds = (end + PMD_SIZE - 1) >> PMD_SHIFT;
 	tables = round_up(puds * sizeof(pud_t), PAGE_SIZE) +
 		 round_up(pmds * sizeof(pmd_t), PAGE_SIZE);
 
-	table_start = find_e820_area(0x8000, __pa_symbol(&_text), tables);
+	/* Put page tables beyond the DMA zones if possible.
+	   RED-PEN might be better to spread them out more over
+	   memory to avoid hotspots */
+	if (end > MAX_DMA32_PFN<<PAGE_SHIFT)
+		start = MAX_DMA32_PFN << PAGE_SHIFT;
+	else if (end > MAX_DMA_PFN << PAGE_SHIFT)
+		start = MAX_DMA_PFN << PAGE_SHIFT;
+	else
+		start = 0x8000;
+
+	table_start = find_e820_area(start, end, tables);
+	if (table_start == -1)
+		table_start = find_e820_area(0x8000, end, tables);
 	if (table_start == -1UL)
 		panic("Cannot find space for the kernel page tables");