On 04/27/2009 09:24 PM, Jens Axboe wrote:
> On Mon, Apr 27 2009, Boaz Harrosh wrote:
Jens Hi, Thanks for your reply. Please I need some help with
this.
>>> +static struct bio *bio_chain_clone(struct bio *old_chain, gfp_t gfpmask)
>>> +{
>>> + struct bio *tmp, *new_chain = NULL, *tail = NULL;
>>> +
>>> + while (old_chain) {
>>> + tmp = bio_clone(old_chain, gfpmask);
>>> + if (!tmp)
>>> + goto err_out;
>>> +
>>> + tmp->bi_next = NULL;
>>> + if (!new_chain)
>>> + new_chain = tail = tmp;
>>> + else {
>>> + tail->bi_next = tmp;
>>> + tail = tmp;
>>> + }
>>> +
>>> + old_chain = old_chain->bi_next;
>>> + }
>>> +
>>> + return new_chain;
>>> +
>>> +err_out:
>>> + bio_chain_put(new_chain);
>>> + return NULL;
>>> +}
>>> +
>> NOTE-TO-ME:
>> blk_bio_clone()
>
> Note to Boaz - this is illegal, unless gfp_mask is GFP_ATOMIC (in which
> case you should not pass it in).
OK it is only used with GFP_ATOMIC.
Theoretically, what if I use a thread and am aloud to sleep,
(and executing requests in serial). Can I then wait on the first bio_clone.
> The only way to make this work is to:
>
Are you saying that, in the case I'm a swap device? or do you mean that if I
use the above code I can break it for other devices that are swap-devices
and cause a live lock for them.
Currently the OSD library is not swap safe. And even if it was, iSCSI is not.
So there is no option of this ever been swap.
> 1) Have a private bio pool, and
Do I need to manage such a pool internally and use __bio_clone() or is there
an easy way to associate a private bio-pool to a request_queue?
> 2) Make sure it has enough reserved entries to populate the chain
Is there a system limit to that, that I can be sure of? Or just choose
a magic number and if it is exceeded just split the io up in parts?
> 3) Ensure only a single caller at the time, or entries enough for the N
> users that are allowed. It has to be controlled either way, whether N
> is 1 or larger.
osdblk_rq_fn (the queue fn) is it serialized to one thread? If not
could I use the queue lock for the duration of the clone?
>
Thanks for your help
Boaz
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