Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx> writes:
> On 07/16/2018 05:55 PM, Huang, Ying wrote:
>> +/*
>> + * For non-HDD swap devices, the fine grained cluster lock is used to
>> + * protect si->swap_map. But cluster and cluster locks isn't
>> + * available for HDD, so coarse grained si->lock will be used instead
>> + * for that.
>> + */
>> static inline struct swap_cluster_info *lock_cluster_or_swap_info(
>> struct swap_info_struct *si,
>> unsigned long offset)
>
> This nomenclature is not consistent with the rest of the file. We call
> a "non-HDD" device an "ssd" absolutely everywhere else in the file. Why
> are you calling it a non-HDD here? (fwiw, HDD _barely_ hits my acronym
> cache anyway).
>
> How about this?
>
> /*
> * Determine the locking method in use for this device. Return
> * swap_cluster_info if SSD-style cluster-based locking is in place.
> */
> static inline struct swap_cluster_info *lock_cluster_or_swap_info(
> struct swap_info_struct *si,
> unsigned long offset)
> {
> struct swap_cluster_info *ci;
>
> /* Try to use fine-grained SSD-style locking if available: */
> ci = lock_cluster(si, offset);
>
> /* Otherwise, fall back to traditional, coarse locking: */
> if (!ci)
> spin_lock(&si->lock);
>
> return ci;
> }
This is better than my one, will use this. Thanks!
> Which reminds me? Why do we even bother having two locking models?
Because si->cluster_info is NULL for non-SSD, so we cannot use cluster
lock.
About why not use struct swap_cluster_info for non-SSD? Per my
understanding, struct swap_cluster_info is optimized for SSD.
Especially it assumes seeking is cheap. So different free swap slot
scanning policy is used for SSD and non-SSD.
Best Regards,
Huang, Ying
