[PATCH] nommu: yield CPU periodically while disposing large VM

["Steven J. Magnani" <steve@digidescorp.com>]

Depending on processor speed, page size, and the amount of memory a process
is allowed to amass, cleanup of a large VM may freeze the system for many
seconds. This can result in a watchdog timeout.

Make sure other tasks receive some service when cleaning up large VMs.

Signed-off-by: Steven J. Magnani <steve@digidescorp.com>
---
diff -uprN a/mm/nommu.c b/mm/nommu.c
--- a/mm/nommu.c	2010-10-21 07:42:23.000000000 -0500
+++ b/mm/nommu.c	2010-10-21 07:46:50.000000000 -0500
@@ -1656,6 +1656,7 @@ SYSCALL_DEFINE2(munmap, unsigned long, a
 void exit_mmap(struct mm_struct *mm)
 {
 	struct vm_area_struct *vma;
+	unsigned long next_yield = jiffies + HZ;
 
 	if (!mm)
 		return;
@@ -1668,6 +1669,11 @@ void exit_mmap(struct mm_struct *mm)
 		mm->mmap = vma->vm_next;
 		delete_vma_from_mm(vma);
 		delete_vma(mm, vma);
+		/* Yield periodically to prevent watchdog timeout */
+		if (time_after(jiffies, next_yield)) {
+			cond_resched();
+			next_yield = jiffies + HZ;
+		}
 	}
 
 	kleave("");

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