Messages in this thread | | | Date | Wed, 8 Jun 2022 13:34:26 +0530 | Subject | Re: [PATCH v5 1/9] mm/demotion: Add support for explicit memory tiers | From | Aneesh Kumar K V <> |
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On 6/8/22 11:40 AM, Ying Huang wrote: > On Wed, 2022-06-08 at 10:07 +0530, Aneesh Kumar K V wrote: >> On 6/8/22 12:13 AM, Tim Chen wrote: >> ... >> >>>> >>>> + >>>> +static void memory_tier_device_release(struct device *dev) >>>> +{ >>>> + struct memory_tier *tier = to_memory_tier(dev); >>>> + >>> >>> Do we need some ref counts on memory_tier? >>> If there is another device still using the same memtier, >>> free below could cause problem. >>> >>>> + kfree(tier); >>>> +} >>>> + >>>> >>> ... >> >> The lifecycle of the memory_tier struct is tied to the sysfs device life >> time. ie, memory_tier_device_relese get called only after the last >> reference on that sysfs dev object is released. Hence we can be sure >> there is no userspace that is keeping one of the memtier related sysfs >> file open. >> >> W.r.t other memory device sharing the same memtier, we unregister the >> sysfs device only when the memory tier nodelist is empty. That is no >> memory device is present in this memory tier. > > memory_tier isn't only used by user space. It is used inside kernel > too. If some kernel code get a pointer to struct memory_tier, we need > to guarantee the pointer will not be freed under us.
As mentioned above current patchset avoid doing that.
> And as Tim pointed > out, we need to use it in hot path (for statistics), so some kind of rcu > lock may be good. >
Sure when those statistics code get added, we can add the relevant kref and locking details.
-aneesh
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