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From:   =?utf-8?Q?Javier_Gonz=C3=A1lez?= <javier@javigon.com>
Message-Id: <61F640FB-E38C-41CE-B95A-D2CDAA0008EF@javigon.com>
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Subject: Re: [PATCH] lightnvm: pblk: take write semaphore on metadata
Date:   Mon, 13 Aug 2018 14:12:04 +0200
In-Reply-To: <CANr-nt18UvLY7YjUqTDtd-mi+Az-WTMvcbCTC1uVgBpddS=zxQ@mail.gmail.com>
Cc:     =?utf-8?Q?Matias_Bj=C3=B8rling?= <mb@lightnvm.io>,
        linux-block@vger.kernel.org,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
To:     Hans Holmberg <hans.ml.holmberg@owltronix.com>
References: <1533297919-27253-1-git-send-email-javier@cnexlabs.com>
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> On 10 Aug 2018, at 10.04, Hans Holmberg =
<hans.ml.holmberg@owltronix.com> wrote:
>=20
> On Fri, Aug 3, 2018 at 2:05 PM, Javier Gonz=C3=A1lez =
<javier@javigon.com> 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.
>>=20
>> Since metadata I/O 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.
>>=20
>> 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 metdatada scheme could =
cause
>> ordering issues.
>>=20
>> Signed-off-by: Javier Gonz=C3=A1lez <javier@cnexlabs.com>
>> ---
>> drivers/lightnvm/pblk-core.c | 14 ++++++++++++--
>> drivers/lightnvm/pblk.h      |  1 +
>> 2 files changed, 13 insertions(+), 2 deletions(-)
>>=20
>> diff --git a/drivers/lightnvm/pblk-core.c =
b/drivers/lightnvm/pblk-core.c
>> index 00984b486fea..160b54d26bfa 100644
>> --- a/drivers/lightnvm/pblk-core.c
>> +++ b/drivers/lightnvm/pblk-core.c
>> @@ -493,6 +493,16 @@ int pblk_submit_io_sync(struct pblk *pblk, =
struct nvm_rq *rqd)
>>        return nvm_submit_io_sync(dev, rqd);
>> }
>>=20
>> +int pblk_submit_io_sync_sem(struct pblk *pblk, struct nvm_rq *rqd)
>> +{
>> +       if (rqd->opcode !=3D NVM_OP_PWRITE)
>> +               pblk_submit_io_sync(pblk, rqd);
>> +
>> +       pblk_down_page(pblk, rqd->ppa_list, rqd->nr_ppas);
>=20
> This will only work if rqd->nr_ppas > 1, better check if rqd->nr_ppas
> is 1 and pass &ppa->ppa_addr on to pblk_down_page when needed.


For this particular case, we will always get > 1 ppas, but you're right,
it is more robust to do the check for future cases. I'll add that to V3.
Thanks!

Javier

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