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

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Date:   Wed, 29 Aug 2018 13:41:59 +0000
From:   Javier Gonzalez <javier@...xlabs.com>
To:     Matias Bjørling <mb@...htnvm.io>
CC:     Jens Axboe <axboe@...nel.dk>,
        "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 3/3] lightnvm: pblk: take write semaphore on metadata


> On 29 Aug 2018, at 15.40, Matias Bjørling <mb@...htnvm.io> wrote:
> 
> 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.

No hurry. Thanks!

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