UML - Customize tlb.h

Customize the hooks in tlb.h to optimize TLB flushing some more.

Add start and end fields to tlb_gather_mmu, which are used to limit the address space range scanned when a region is unmapped.

The interfaces which just free page tables, without actually changing mappings, don't need to cause a TLB flush.

...

arch/um/kernel/tlb.c +4 -0

+	while (vma != NULL) {
+		fix_range(mm, vma->vm_start, vma->vm_end, 0);
+		vma = vma->vm_next;
+	}
 }
 
 void force_flush_all(void)

Index: linux-2.6-git/include/asm-um/tlb.h
===================================================================

include/asm-um/tlb.h +49 -1

@@ -1,6 +1,125 @@
 #ifndef __UM_TLB_H
 #define __UM_TLB_H
 
-#include <asm/arch/tlb.h>
+#include <linux/swap.h>
+#include <asm/pgalloc.h>
+#include <asm/tlbflush.h>
+
+#define tlb_start_vma(tlb, vma) do { } while (0)
+#define tlb_end_vma(tlb, vma) do { } while (0)
+#define tlb_flush(tlb) flush_tlb_mm((tlb)->mm)
+
+/* struct mmu_gather is an opaque type used by the mm code for passing around
+ * any data needed by arch specific code for tlb_remove_page.
+ */
+struct mmu_gather {
+	struct mm_struct	*mm;
+	unsigned int		need_flush; /* Really unmapped some ptes? */
+	unsigned long		start;
+	unsigned long		end;
+	unsigned int		fullmm; /* non-zero means full mm flush */
+};
+
+/* Users of the generic TLB shootdown code must declare this storage space. */
+DECLARE_PER_CPU(struct mmu_gather, mmu_gathers);
+
+static inline void __tlb_remove_tlb_entry(struct mmu_gather *tlb, pte_t *ptep,
+					  unsigned long address)
+{
+	if (tlb->start > address)
+		tlb->start = address;
+	if (tlb->end < address + PAGE_SIZE)
+		tlb->end = address + PAGE_SIZE;
+}
+
+static inline void init_tlb_gather(struct mmu_gather *tlb)
+{
+	tlb->need_flush = 0;
+
+	tlb->start = TASK_SIZE;
+	tlb->end = 0;
+
+	if (tlb->fullmm) {
+		tlb->start = 0;
+		tlb->end = TASK_SIZE;
+	}
+}
+
+/* tlb_gather_mmu
+ *	Return a pointer to an initialized struct mmu_gather.
+ */
+static inline struct mmu_gather *
+tlb_gather_mmu(struct mm_struct *mm, unsigned int full_mm_flush)

arch/um/kernel/tlb.c void flush_tlb_mm(struct mm_struct *mm) · line 521

Quoted 6 lines

arch/um/kernel/tlb.c +6 -0

+void flush_tlb_mm(struct mm_struct *mm)
+{
+	struct vm_area_struct *vma = mm->mmap;
+
+	if (atomic_read(&mm->mm_users) == 0)
+		return;

Under which circumstances does this test succeed?

This file rather needs an inclusion of percpu.h. I guess you got lucky.