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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>
This commit is contained in:
Nick Piggin 2007-05-06 14:49:53 -07:00 committed by Linus Torvalds
parent b4169525bc
commit 0a27a14a62
1 changed files with 29 additions and 4 deletions
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33
mm/madvise.c
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@ -11,6 +11,24 @@
#include <linux/mempolicy.h>
#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;
}