Revert "mm/vmalloc: interchage the implementation of vmalloc_to_{pfn,page}"
Revert commit ece86e222db4, which was intended as a small performance
improvement.
Despite the claim that the patch doesn't introduce any functional
changes in fact it does.
The "no page" path behaves different now. Originally, vmalloc_to_page
might return NULL under some conditions, with new implementation it
returns pfn_to_page(0) which is not the same as NULL.
Simple test shows the difference.
test.c
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/vmalloc.h>
#include <linux/mm.h>
int __init myi(void)
{
struct page *p;
void *v;
v = vmalloc(PAGE_SIZE);
/* trigger the "no page" path in vmalloc_to_page*/
vfree(v);
p = vmalloc_to_page(v);
pr_err("expected val = NULL, returned val = %p", p);
return -EBUSY;
}
void __exit mye(void)
{
}
module_init(myi)
module_exit(mye)
Before interchange:
expected val = NULL, returned val = (null)
After interchange:
expected val = NULL, returned val = c7ebe000
Signed-off-by: Vladimir Murzin <murzin.v@gmail.com>
Cc: Jianyu Zhan <nasa4836@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
1 file changed