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

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Message-Id: <1287665635-7925-1-git-send-email-steve@digidescorp.com>
Date:	Thu, 21 Oct 2010 07:53:55 -0500
From:	"Steven J. Magnani" <steve@...idescorp.com>
To:	linux-mm@...ck.org
Cc:	dhowells@...hat.com, linux-kernel@...r.kernel.org,
	"Steven J. Magnani" <steve@...idescorp.com>
Subject: [PATCH] nommu: yield CPU periodically while disposing large VM

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@...idescorp.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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