> On 26 Jun 2018, at 13.44, Matias Bjørling <mb@xxxxxxxxxxx> wrote:
>
>> On 06/26/2018 01:31 PM, Hans Holmberg wrote:
>>> On Tue, Jun 26, 2018 at 1:38 PM, Matias Bjørling <mb@xxxxxxxxxxx> wrote:
>>>> On 06/26/2018 11:37 AM, Javier Gonzalez wrote:
>>>>
>>>>
>>>>
>>>>> On 26 Jun 2018, at 10.41, Matias Bjørling <mb@xxxxxxxxxxx> wrote:
>>>>>
>>>>> On 06/19/2018 11:06 AM, Hans Holmberg wrote:
>>>>>>
>>>>>> From: Hans Holmberg <hans.holmberg@xxxxxxxxxxxx>
>>>>>> We can't know if a block is closed or not on 1.2 devices, so assume
>>>>>> closed state to make sure that blocks are erased before writing.
>>>>>> Fixes: 32ef9412c114 ("lightnvm: pblk: implement get log report chunk")
>>>>>> Signed-off-by: Hans Holmberg <hans.holmberg@xxxxxxxxxxxx>
>>>>>> ---
>>>>>> This patch applies on:
>>>>>> ssh://github.com/OpenChannelSSD/linux branch for-4.19/core
>>>>>> drivers/lightnvm/pblk-init.c | 5 +++--
>>>>>> 1 file changed, 3 insertions(+), 2 deletions(-)
>>>>>> diff --git a/drivers/lightnvm/pblk-init.c b/drivers/lightnvm/pblk-init.c
>>>>>> index aa24264..3b8aa4a 100644
>>>>>> --- a/drivers/lightnvm/pblk-init.c
>>>>>> +++ b/drivers/lightnvm/pblk-init.c
>>>>>> @@ -717,10 +717,11 @@ static int pblk_setup_line_meta_12(struct pblk
>>>>>> *pblk, struct pblk_line *line,
>>>>>> /*
>>>>>> * In 1.2 spec. chunk state is not persisted by the
>>>>>> device. Thus
>>>>>> - * some of the values are reset each time pblk is
>>>>>> instantiated.
>>>>>> + * some of the values are reset each time pblk is
>>>>>> instantiated,
>>>>>> + * so we have to assume that the block is closed.
>>>>>> */
>>>>>> if (lun_bb_meta[line->id] == NVM_BLK_T_FREE)
>>>>>> - chunk->state = NVM_CHK_ST_FREE;
>>>>>> + chunk->state = NVM_CHK_ST_CLOSED;
>>>>>> else
>>>>>> chunk->state = NVM_CHK_ST_OFFLINE;
>>>>>>
>>>>>
>>>>> pblk should scan (or the lightnvm subsystem) the blocks for their
>>>>> state, such that it doesn't have to reinitialize a full drive if it is
>>>>> already in a closed state. If marking closed, it does a full erase
>>>>> cycle on initialization, which should be avoided since it is a limited
>>>>> resource.
>>>>
>>>>
>>>> In 1.2 there is no such state unfortunately. However, pblk will never
>>>> attempt to reinitialize the whole drive - metadata for closed blocks
>>>> will be recovered and only those going to GC will be erased before
>>>> usage. In fact, a full close drive is the state pblk expects.
>>>>
>>>> This patch only affects "unknown blocks", thus the only case in which
>>>> pblk would attempt to double erase is when blocks have been pre-erased
>>>> (e.g., factory or through liblightnvm). After an erase round though,
>>>> pblk will only erase pre-usage. One thing we could do is attempting to
>>>> read the first page of these unknown blocks and mark them as free if
>>>> "empty page" is returned. Is this what you mean?
>>>
>>>
>>> Yes, that is what I mean.
>>>
>>> Note that this can be
>>>>
>>>> costly on large drives; this is the reason we returned to the pre-2.0
>>>> behaviour with this patch. We are implementing a log that, among other
>>>> things, keeps the state so that pblk can have an accurate state for the
>>>> cases this can be a problem.
>>>
>>>
>>> Yep, it will take some time. Good to hear with the log.
>> Until we have a log in place, this patch unbreaks 1.2 support and has
>> no negative impact on performance (as compared to pre 2.0 support), so
>> please consider it for the next window.
>> The current state is that if a pblk instance is created on a 1.2 disk
>> with written blocks, writes will fail.
>> / Hans
>
> The negative impact is that all blocks are erased, even if they are in free state. This is a showstopper. We cannot throw out 1/X of the lifetime of the drive on each initialization. The 1.2 spec is made such that a scan can recover the block state accurately.
This fixes patch returns to the original behavior, so it’s not introducing a worse behavior than before 2.0. But you’re right, it is not the way it should be.
Can you consider taking this as a fix for 4.18 to avoid writes failing on 1.2 devices and I promise to send a patch this week to implement the state based on reads? This new patch would be for 4.19.
Javier
