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

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Message-ID: <0FD404FB-C660-412B-9658-454A9DCD7558@cnexlabs.com>
Date:   Wed, 29 Aug 2018 13:21:49 +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 15.08, 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?


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