[patch] sched, mm: fix scheduling latencies in filemap_sync()

[Ingo Molnar <mingo@elte.hu>]

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The attached patch, written by Andrew Morton, fixes long scheduling
latencies in filemap_sync().

has been tested as part of the -VP patchset.

	Ingo

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The attached patch, written by Andrew Morton, fixes long scheduling
latencies in filemap_sync().

has been tested as part of the -VP patchset.

Signed-off-by: Ingo Molnar <mingo@elte.hu>

--- linux/mm/msync.c.orig	
+++ linux/mm/msync.c	
@@ -92,8 +92,8 @@ static inline int filemap_sync_pmd_range
 	return error;
 }
 
-static int filemap_sync(struct vm_area_struct * vma, unsigned long address,
-	size_t size, unsigned int flags)
+static int __filemap_sync(struct vm_area_struct *vma, unsigned long address,
+			size_t size, unsigned int flags)
 {
 	pgd_t * dir;
 	unsigned long end = address + size;
@@ -131,6 +131,31 @@ static int filemap_sync(struct vm_area_s
 	return error;
 }
 
+#ifdef CONFIG_PREEMPT
+static int filemap_sync(struct vm_area_struct *vma, unsigned long address,
+			size_t size, unsigned int flags)
+{
+	const size_t chunk = 64 * 1024;	/* bytes */
+	int error = 0;
+
+	while (size) {
+		size_t sz = min(size, chunk);
+
+		error |= __filemap_sync(vma, address, sz, flags);
+		cond_resched();
+		address += sz;
+		size -= sz;
+	}
+	return error;
+}
+#else
+static int filemap_sync(struct vm_area_struct *vma, unsigned long address,
+			size_t size, unsigned int flags)
+{
+	return __filemap_sync(vma, address, size, flags);
+}
+#endif
+
 /*
  * MS_SYNC syncs the entire file - including mappings.
  *