Messages in this thread | | | From | "Huang\, Ying" <> | Subject | Re: [PATCH v2 1/7] swap: Add comments to lock_cluster_or_swap_info() | Date | Wed, 18 Jul 2018 11:09:25 +0800 |
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Dave Hansen <dave.hansen@linux.intel.com> 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
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