> On Oct 16, 2018, at 8:26 PM, liu.song11@xxxxxxxxxx wrote:
>
>> On Tue, Oct 16, 2018 at 10:55:26PM +0800, fishland wrote:
>>> The jinode does not need protected by *i_lock*, we can return
>>> directly if memory allocation fails.
>>>
>>
>> I don't see anything wrong with this patch, but at the same time, I'm
>> not sure I see the benefit, either. Checking for the allocation
>> failure is cheap, and moving it out spinlock doesn't buy much; not to
>> mention that the allocation failure is going to be highly uncommon.
>>
>> What inspired this commit?
>>
>> - Ted
>
> Hi, Ted
> I found this during code reading. All code logic is very smooth, when
> reading here, need to spin_unlock before "return -ENOMEM", which I
> feel this could more close to the allocate. I refer to other processing
> logic for this situation in "inode.c", found that they all return immediately
> after memory application failed. I agree with you that the benefit of this
> patch is almost none, however it can slightly improve the code in rare case.
Looking at the patch there are two effects that it has:
- optimize a very rare case where there is an allocation failure before locking
- return an unnecessary error if "ei->jinode" is allocated before locking
I don't think it is worthwhile to optimize this case, since allocation failures
will have a serious impact on the application, and I'd rather avoid the rare
case where we don't return an unnecessary error than make the error case faster.
Cheers, Andreas
>
>>> Signed-off-by: Liu Song <liu.song11@xxxxxxxxxx>
>>> Reviewed-by: Wang Yi <wang.yi59@xxxxxxxxxx>
>>> ---
>>> fs/ext4/inode.c | 7 +++----
>>> 1 file changed, 3 insertions(+), 4 deletions(-)
>>>
>>> diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
>>> index d767e993591d..67ba6f062de5 100644
>>> --- a/fs/ext4/inode.c
>>> +++ b/fs/ext4/inode.c
>>> @@ -4384,12 +4384,11 @@ int ext4_inode_attach_jinode(struct inode *inode)
>>> return 0;
>>>
>>> jinode = jbd2_alloc_inode(GFP_KERNEL);
>>> + if (!jinode)
>>> + return -ENOMEM;
>>> +
>>> spin_lock(&inode->i_lock);
>>> if (!ei->jinode) {
>>> - if (!jinode) {
>>> - spin_unlock(&inode->i_lock);
>>> - return -ENOMEM;
>>> - }
>>> ei->jinode = jinode;
>>> jbd2_journal_init_jbd_inode(ei->jinode, inode);
>>> jinode = NULL;
>>> --
>>> 2.17.1
Cheers, Andreas
Attachment:
signature.asc
Description: Message signed with OpenPGP
