On Thu, Jun 28, 2012 at 10:57:21PM +0100, Benjamin Herrenschmidt wrote:
> On Thu, 2012-06-28 at 18:52 +0200, Peter Zijlstra wrote:
> > No I think you're right (as always).. also an IPI will not force
> > schedule the thread that might be running on the receiving cpu, also
> > we'd have to wait for any such schedule to complete in order to
> > guarantee the mm isn't lazily used anymore.
> >
> > Bugger..
>
> You can still do it if the mm count is 1 no ? Ie, current is the last
> holder of a reference to the mm struct... which will probably be the
> common case for short lived programs.
BTW, can we not move the free_pgtables() call in exit_mmap() to
__mmdrop()? Something like below but I'm not entirely sure about its
implications:
diff --git a/include/linux/mm.h b/include/linux/mm.h
index b36d08c..507ee9f 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1372,6 +1372,7 @@ extern void unlink_file_vma(struct vm_area_struct *);
extern struct vm_area_struct *copy_vma(struct vm_area_struct **,
unsigned long addr, unsigned long len, pgoff_t pgoff);
extern void exit_mmap(struct mm_struct *);
+extern void exit_pgtables(struct mm_struct *mm);
extern int mm_take_all_locks(struct mm_struct *mm);
extern void mm_drop_all_locks(struct mm_struct *mm);
diff --git a/kernel/fork.c b/kernel/fork.c
index ab5211b..3412b1a 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -588,6 +588,7 @@ struct mm_struct *mm_alloc(void)
void __mmdrop(struct mm_struct *mm)
{
BUG_ON(mm == &init_mm);
+ exit_pgtables(mm);
mm_free_pgd(mm);
destroy_context(mm);
mmu_notifier_mm_destroy(mm);
diff --git a/mm/mmap.c b/mm/mmap.c
index 074b487..d9ebfdb 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -2269,7 +2269,6 @@ void exit_mmap(struct mm_struct *mm)
{
struct mmu_gather tlb;
struct vm_area_struct *vma;
- unsigned long nr_accounted = 0;
/* mm's last user has gone, and its about to be pulled down */
mmu_notifier_release(mm);
@@ -2291,11 +2290,23 @@ void exit_mmap(struct mm_struct *mm)
lru_add_drain();
flush_cache_mm(mm);
- tlb_gather_mmu(&tlb, mm, 1);
+ tlb_gather_mmu(&tlb, mm, 0);
/* update_hiwater_rss(mm) here? but nobody should be looking */
/* Use -1 here to ensure all VMAs in the mm are unmapped */
unmap_vmas(&tlb, vma, 0, -1);
+ tlb_finish_mmu(&tlb, 0, -1);
+}
+
+void exit_pgtables(struct mm_struct *mm)
+{
+ struct mmu_gather tlb;
+ struct vm_area_struct *vma;
+ unsigned long nr_accounted = 0;
+ vma = mm->mmap;
+ if (!vma)
+ return;
+ tlb_gather_mmu(&tlb, mm, 1);
free_pgtables(&tlb, vma, FIRST_USER_ADDRESS, TASK_SIZE);
tlb_finish_mmu(&tlb, 0, -1);
--
Catalin
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