[RFC PATCH 3/4] mm/vmalloc.c: Allow lowmem to be tracked in vmalloc

[Laura Abbott]

vmalloc is currently assumed to be a completely separate address space
from the lowmem region. While this may be true in the general case,
there are some instances where lowmem and virtual space intermixing
provides gains. One example is needing to steal a large chunk of physical
lowmem for another purpose outside the systems usage. Rather than
waste the precious lowmem space on a 32-bit system, we can allow the
virtual holes created by the physical holes to be used by vmalloc
for virtual addressing. Track lowmem allocations in vmalloc to
allow mixing of lowmem and vmalloc.

Signed-off-by: Laura Abbott <lauraa at codeaurora.org>
Signed-off-by: Neeti Desai <neetid at codeaurora.org>
---
 include/linux/mm.h      |    6 ++++++
 include/linux/vmalloc.h |    1 +
 mm/Kconfig              |   11 +++++++++++
 mm/vmalloc.c            |   26 ++++++++++++++++++++++++++
 4 files changed, 44 insertions(+), 0 deletions(-)

diff --git a/include/linux/mm.h b/include/linux/mm.h
index f022460..76df50d 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -308,6 +308,10 @@ unsigned long vmalloc_to_pfn(const void *addr);
  * On nommu, vmalloc/vfree wrap through kmalloc/kfree directly, so there
  * is no special casing required.
  */
+
+#ifdef CONFIG_VMALLOC_SAVING
+extern int is_vmalloc_addr(const void *x)
+#else
 static inline int is_vmalloc_addr(const void *x)
 {
 #ifdef CONFIG_MMU
@@ -318,6 +322,8 @@ static inline int is_vmalloc_addr(const void *x)
 	return 0;
 #endif
 }
+#endif
+
 #ifdef CONFIG_MMU
 extern int is_vmalloc_or_module_addr(const void *x);
 #else
diff --git a/include/linux/vmalloc.h b/include/linux/vmalloc.h
index 4b8a891..e0c8c49 100644
--- a/include/linux/vmalloc.h
+++ b/include/linux/vmalloc.h
@@ -16,6 +16,7 @@ struct vm_area_struct;		/* vma defining user mapping in mm_types.h */
 #define VM_USERMAP		0x00000008	/* suitable for remap_vmalloc_range */
 #define VM_VPAGES		0x00000010	/* buffer for pages was vmalloc'ed */
 #define VM_UNINITIALIZED	0x00000020	/* vm_struct is not fully initialized */
+#define VM_LOWMEM		0x00000040	/* Tracking of direct mapped lowmem */
 /* bits [20..32] reserved for arch specific ioremap internals */
 
 /*
diff --git a/mm/Kconfig b/mm/Kconfig
index 8028dcc..b3c459d 100644
--- a/mm/Kconfig
+++ b/mm/Kconfig
@@ -519,3 +519,14 @@ config MEM_SOFT_DIRTY
 	  it can be cleared by hands.
 
 	  See Documentation/vm/soft-dirty.txt for more details.
+
+config ENABLE_VMALLOC_SAVING
+	bool "Intermix lowmem and vmalloc virtual space"
+	depends on ARCH_TRACKS_VMALLOC
+	help
+	  Some memory layouts on embedded systems steal large amounts
+	  of lowmem physical memory for purposes outside of the kernel.
+	  Rather than waste the physical and virtual space, allow the
+	  kernel to use the virtual space as vmalloc space.
+
+	  If unsure, say N.
diff --git a/mm/vmalloc.c b/mm/vmalloc.c
index 13a5495..c7b138b 100644
--- a/mm/vmalloc.c
+++ b/mm/vmalloc.c
@@ -204,6 +204,29 @@ static int vmap_page_range(unsigned long start, unsigned long end,
 	return ret;
 }
 
+#ifdef ENABLE_VMALLOC_SAVING
+int is_vmalloc_addr(const void *x)
+{
+	struct rb_node *n;
+	struct vmap_area *va;
+	int ret = 0;
+
+	spin_lock(&vmap_area_lock);
+
+	for (n = rb_first(vmap_area_root); n; rb_next(n)) {
+		va = rb_entry(n, struct vmap_area, rb_node);
+		if (x >= va->va_start && x < va->va_end) {
+			ret = 1;
+			break;
+		}
+	}
+
+	spin_unlock(&vmap_area_lock);
+	return ret;
+}
+EXPORT_SYMBOL(is_vmalloc_addr);
+#endif
+
 int is_vmalloc_or_module_addr(const void *x)
 {
 	/*
@@ -2628,6 +2651,9 @@ static int s_show(struct seq_file *m, void *p)
 	if (v->flags & VM_VPAGES)
 		seq_printf(m, " vpages");
 
+	if (v->flags & VM_LOWMEM)
+		seq_printf(m, " lowmem");
+
 	show_numa_info(m, v);
 	seq_putc(m, '\n');
 	return 0;
-- 
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