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authorNick Piggin <npiggin@suse.de>2007-05-06 14:49:53 -0700
committerLinus Torvalds <torvalds@woody.linux-foundation.org>2007-05-07 12:12:54 -0700
commit0a27a14a62921b438bb6f33772690d345a089be6 (patch)
tree3a0a23880832ded1160b60a93300f4248a7de91f
parentb4169525bc2336ea6581c6ff2aa88b2671e3b9f9 (diff)
mm: madvise avoid exclusive mmap_sem
Avoid down_write of the mmap_sem in madvise when we can help it. Acked-by: Hugh Dickins <hugh@veritas.com> Signed-off-by: Nick Piggin <npiggin@suse.de> Cc: Rik van Riel <riel@redhat.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
-rw-r--r--mm/madvise.c33
1 files changed, 29 insertions, 4 deletions
diff --git a/mm/madvise.c b/mm/madvise.c
index 603c5257ed6e..e75096b5a6d3 100644
--- a/mm/madvise.c
+++ b/mm/madvise.c
@@ -12,6 +12,24 @@
#include <linux/hugetlb.h>
/*
+ * Any behaviour which results in changes to the vma->vm_flags needs to
+ * take mmap_sem for writing. Others, which simply traverse vmas, need
+ * to only take it for reading.
+ */
+static int madvise_need_mmap_write(int behavior)
+{
+ switch (behavior) {
+ case MADV_REMOVE:
+ case MADV_WILLNEED:
+ case MADV_DONTNEED:
+ return 0;
+ default:
+ /* be safe, default to 1. list exceptions explicitly */
+ return 1;
+ }
+}
+
+/*
* We can potentially split a vm area into separate
* areas, each area with its own behavior.
*/
@@ -183,9 +201,9 @@ static long madvise_remove(struct vm_area_struct *vma,
+ ((loff_t)vma->vm_pgoff << PAGE_SHIFT);
/* vmtruncate_range needs to take i_mutex and i_alloc_sem */
- up_write(&current->mm->mmap_sem);
+ up_read(&current->mm->mmap_sem);
error = vmtruncate_range(mapping->host, offset, endoff);
- down_write(&current->mm->mmap_sem);
+ down_read(&current->mm->mmap_sem);
return error;
}
@@ -270,7 +288,10 @@ asmlinkage long sys_madvise(unsigned long start, size_t len_in, int behavior)
int error = -EINVAL;
size_t len;
- down_write(&current->mm->mmap_sem);
+ if (madvise_need_mmap_write(behavior))
+ down_write(&current->mm->mmap_sem);
+ else
+ down_read(&current->mm->mmap_sem);
if (start & ~PAGE_MASK)
goto out;
@@ -332,6 +353,10 @@ asmlinkage long sys_madvise(unsigned long start, size_t len_in, int behavior)
vma = find_vma(current->mm, start);
}
out:
- up_write(&current->mm->mmap_sem);
+ if (madvise_need_mmap_write(behavior))
+ up_write(&current->mm->mmap_sem);
+ else
+ up_read(&current->mm->mmap_sem);
+
return error;
}