zsmalloc: fix obj_to_head use page_private(page) as value but not pointer
authorHui Zhu <zhuhui@xiaomi.com>
Sat, 7 Nov 2015 00:29:26 +0000 (16:29 -0800)
committerLinus Torvalds <torvalds@linux-foundation.org>
Sat, 7 Nov 2015 01:50:42 +0000 (17:50 -0800)
commit12a7bfad58cd604616dd5205efa6dc2be6f299eb
tree29228fe2c4440e1d95eeb64a8c19ef889f9bf744
parent8f958c98f28d088a1ef3e021ab7aeb59a234b953
zsmalloc: fix obj_to_head use page_private(page) as value but not pointer

In obj_malloc():

if (!class->huge)
/* record handle in the header of allocated chunk */
link->handle = handle;
else
/* record handle in first_page->private */
set_page_private(first_page, handle);

In the hugepage we save handle to private directly.

But in obj_to_head():

if (class->huge) {
VM_BUG_ON(!is_first_page(page));
return *(unsigned long *)page_private(page);
} else
return *(unsigned long *)obj;

It is used as a pointer.

The reason why there is no problem until now is huge-class page is born
with ZS_FULL so it can't be migrated.  However, we need this patch for
future work: "VM-aware zsmalloced page migration" to reduce external
fragmentation.

Signed-off-by: Hui Zhu <zhuhui@xiaomi.com>
Acked-by: Minchan Kim <minchan@kernel.org>
Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
mm/zsmalloc.c