On 07/20/2012 09:49 AM, Mel Gorman wrote:
+retry:
mutex_lock(&mapping->i_mmap_mutex);
vma_prio_tree_foreach(svma,&iter,&mapping->i_mmap, idx, idx) {
if (svma == vma)
continue;
+ if (svma->vm_mm == vma->vm_mm)
+ continue;
+
+ /*
+ * The target mm could be in the process of tearing down
+ * its page tables and the i_mmap_mutex on its own is
+ * not sufficient. To prevent races against teardown and
+ * pagetable updates, we acquire the mmap_sem and pagetable
+ * lock of the remote address space. down_read_trylock()
+ * is necessary as the other process could also be trying
+ * to share pagetables with the current mm. In the fork
+ * case, we are already both mm's so check for that
+ */
+ if (locked_mm != svma->vm_mm) {
+ if (!down_read_trylock(&svma->vm_mm->mmap_sem)) {
+ mutex_unlock(&mapping->i_mmap_mutex);
+ goto retry;
+ }
+ smmap_sem =&svma->vm_mm->mmap_sem;
+ }
+
+ spage_table_lock =&svma->vm_mm->page_table_lock;
+ spin_lock_nested(spage_table_lock, SINGLE_DEPTH_NESTING);
saddr = page_table_shareable(svma, vma, addr, idx);
if (saddr) {
Hi Mel, FYI I tried this and ran into a problem. When there are
multiple processes
in huge_pmd_share() just faulting in the same i_map they all have their
mmap_sem
down for write so the down_read_trylock(&svma->vm_mm->mmap_sem) never
succeeds. What am I missing?
Thanks, Larry
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