linux-kernel - Re: [PATCH 3/3] lightnvm: pblk: take write semaphore on metadata

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Date:   Wed, 29 Aug 2018 15:40:26 +0200
From:   Matias Bjørling <mb@...htnvm.io>
To:     javier@...xlabs.com
Cc:     axboe@...nel.dk, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] lightnvm: pblk: take write semaphore on metadata

On 08/29/2018 03:21 PM, Javier Gonzalez wrote:
>> On 29 Aug 2018, at 15.08, Matias Bjørling <mb@...htnvm.io> wrote:
>>
>> On 08/29/2018 10:56 AM, Javier González wrote:
>>> pblk guarantees write ordering at a chunk level through a per open chunk
>>> semaphore. At this point, since we only have an open I/O stream for both
>>> user and GC data, the semaphore is per parallel unit.
>>> For the metadata I/O that is synchronous, the semaphore is not needed as
>>> ordering is guaranteed. However, if the metadata scheme changes or
>>> multiple streams are open, this guarantee might not be preserved.
>>> This patch makes sure that all writes go through the semaphore, even for
>>> synchronous I/O. This is consistent with pblk's write I/O model. It also
>>> simplifies maintenance since changes in the metadata scheme could cause
>>> ordering issues.
>>> Signed-off-by: Javier González <javier@...xlabs.com>
>>> ---
>>>   drivers/lightnvm/pblk-core.c | 16 +++++++++++++++-
>>>   drivers/lightnvm/pblk.h      |  1 +
>>>   2 files changed, 16 insertions(+), 1 deletion(-)
>>> diff --git a/drivers/lightnvm/pblk-core.c b/drivers/lightnvm/pblk-core.c
>>> index 767178185f19..1e4dc0c1ed88 100644
>>> --- a/drivers/lightnvm/pblk-core.c
>>> +++ b/drivers/lightnvm/pblk-core.c
>>> @@ -558,6 +558,20 @@ int pblk_submit_io_sync(struct pblk *pblk, struct nvm_rq *rqd)
>>>   	return ret;
>>>   }
>>>   +int pblk_submit_io_sync_sem(struct pblk *pblk, struct nvm_rq *rqd)
>>> +{
>>> +	struct ppa_addr *ppa_list;
>>> +	int ret;
>>> +
>>> +	ppa_list = (rqd->nr_ppas > 1) ? rqd->ppa_list : &rqd->ppa_addr;
>>> +
>>> +	pblk_down_page(pblk, ppa_list, rqd->nr_ppas);
>>
>> If the debug stuff is killed inside __pblk_down_page, then ppa_list
>> and rqd->nr_ppas does not need to be passed, and this function can be
>> inlined in its caller. Can we kill it? I'll make the patch if you
>> like.
> 
> Sounds good. Sure, please send - should I wait to resend this series?
> 

Will do. Yes, wait a bit. I'll post asap.