[PATCH] md/dm-ioctl.c: optimize memory allocation in copy_params

[xinhui.pan]

KMALLOC_MAX_SIZE is too big, it easily cause memory fragmented and low memory when param_kernel->data_size
is also big. That's not nice. So use vmalloc instead of kmalloc when size is larger than (PAGE_SIZE << 2).
There are other drivers using kmalloc to gain a big size memory. And that cause our devices to hit hang and
many worse issues. We don't benefit much when using kmalloc in such scenario.

Signed-off-by: xinhui.pan <xinhuiX.pan@xxxxxxxxx>
Signed-off-by: yanmin.zhang <yanmin_zhang@xxxxxxxxxxxxxxx>
---
 drivers/md/dm-ioctl.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/md/dm-ioctl.c b/drivers/md/dm-ioctl.c
index 5152142..31c3af9 100644
--- a/drivers/md/dm-ioctl.c
+++ b/drivers/md/dm-ioctl.c
@@ -1709,7 +1709,7 @@ static int copy_params(struct dm_ioctl __user *user, struct dm_ioctl *param_kern
         * Use kmalloc() rather than vmalloc() when we can.
         */
        dmi = NULL;
-       if (param_kernel->data_size <= KMALLOC_MAX_SIZE) {
+       if (param_kernel->data_size <= (PAGE_SIZE << 2)) {
                dmi = kmalloc(param_kernel->data_size, GFP_NOIO | __GFP_NORETRY | __GFP_NOMEMALLOC | __GFP_NOWARN);
                if (dmi)
                        *param_flags |= DM_PARAMS_KMALLOC;
-- 
1.7.9.5
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