Re: [GIT PULL] Revert of the IO stat fix

[Jens Axboe]

On 2010-10-24 22:42, Jens Axboe wrote:
> On 2010-10-24 22:35, Linus Torvalds wrote:
>> On Sun, Oct 24, 2010 at 1:09 PM, Jens Axboe <jaxboe@xxxxxxxxxxxx> wrote:
>>>
>>> The fix for cross-partition merges screwing up disk stats turns out
>>> to be problematic on various levels. Lets revert this one so we have
>>> time to come up with a proper solution for this.
>>
>> Hmm.. I think the reverted patch looks like it really is the right
>> thing to do, so I hate reverting it this early. What were the problems
>> with it?
>>
>> Btw, one thing that seems to be missing in the original commit (which
>> is not necessarily the reason for the trouble, of course), is that
>> elv_rq_merge_ok() seems to not check the partition. As far as I can
>> tell, we should have a
>>
>>     if (req->part != bio->bi_bdev->bd_part)
>>        return 0;
>>
>> there, no? And you should _not_ set rq->part in "drive_stat_acct()",
>> you should set it from bio->bi_bdev->bd_part when you create the
>> request.
>>
>> (And if it is NULL, just don't do partition accounting at all)
>>
>> Hmm? What am I missing? What were the bugs?
> 
> The patch itself is sound, the problems are around the area of it not
> really liking non-elevator devices with the elv_quiesce_start/end()
> parts. I had the below patch for that, but then I could not decide
> whether we were fully safe on queue free after talking to Vivek about
> it.

Forgot to include it, here it is. I'll be offline from now and 1-2 days
forward.