Re: [PATCHv2 0/6] dm-zoned: improve cache performance

[Damien Le Moal <Damien.LeMoal@wdc.com>]

On 2020/05/21 3:53, Mike Snitzer wrote:
> On Tue, May 19 2020 at  6:36pm -0400,
> Damien Le Moal <Damien.LeMoal@wdc.com> wrote:
> 
>> On 2020/05/19 17:14, Hannes Reinecke wrote:
>>> Hi all,
>>>
>>> here's an update to dm-zoned to separate out cache zones.
>>> In the update to metadata version 2 the regular drive was split
>>> in emulated zones, which were handled just like 'normal' random
>>> write zones.
>>> This causes a performance drop once these emulated zones have
>>> been mapped, as typicall the random zones from the zoned drive
>>> will perform noticeably slower than those from the regular drive.
>>> (After all, that was kinda the idea of using a regular disk in
>>> the first place ...)
>>>
>>> So in this patchset I've introduced a separate 'cache' zone type,
>>> allowing us to differentiate between emulated and real zones.
>>> With that we can switch the allocation mode to use only cache
>>> zones, and use random zones similar to sequential write zones.
>>> That avoids the performance issue noted above.
>>>
>>> I've also found that the sequential write zones perform noticeably
>>> better on writes (which is all we're caching anyway), so I've
>>> added another patch switching the allocation routine from preferring
>>> sequential write zones for reclaim.
>>>
>>> This patchset also contains some minor fixes like remving an unused
>>> variable etc.
>>>
>>> As usual, comments and reviews are welcome.
>>
>> I ran this overnight with no problems. Throughput results attached.
>> Reclaim seems to be a little too aggressive as it triggers very early. But we
>> can tune that later if really needed: the combination of ext4 writing all over
>> the place and the faster cache zones on SSD may simply result in a percentage of
>> free cache zones becoming low very quickly, in which case, reclaim is working
>> exactly as expected :)
> 
> I've staged this series for 5.8 in linux-next
> 
> Just to make sure no regressions due to all the metadata2 changes: Did
> you happen to verify all worked as expected without using an extra
> drive?

Yes, I did.  Single and dual drive both work fine with v2 metadata.
I will retest the case of a V1 format using V2 code to be extra sure.

> 
>> Mike,
>>
>> With the NVMe io_opt fix patch applied, the alignment warning for the target
>> limits is gone.
> 
> OK
> 
> Thanks,
> Mike
> 
> 


-- 
Damien Le Moal
Western Digital Research