Messages in this thread | | | Subject | Re: [PATCH RFC 1/8] dcache: show count of hash buckets in sysctl fs.dentry-state | From | Konstantin Khlebnikov <> | Date | Fri, 8 May 2020 22:38:10 +0300 |
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On 08/05/2020 22.05, Waiman Long wrote: > On 5/8/20 12:16 PM, Konstantin Khlebnikov wrote: >> On 08/05/2020 17.49, Waiman Long wrote: >>> On 5/8/20 8:23 AM, Konstantin Khlebnikov wrote: >>>> Count of buckets is required for estimating average length of hash chains. >>>> Size of hash table depends on memory size and printed once at boot. >>>> >>>> Let's expose nr_buckets as sixth number in sysctl fs.dentry-state >>> >>> The hash bucket count is a constant determined at boot time. Is there a need to use up one dentry_stat entry for that? Besides one can >>> get it by looking up the kernel dmesg log like: >>> >>> [ 0.055212] Dentry cache hash table entries: 8388608 (order: 14, 67108864 bytes) >> >> Grepping logs since boot time is a worst API ever. >> >> dentry-state shows count of dentries in various states. >> It's very convenient to show count of buckets next to it, >> because this number defines overall scale. > > I am not against using the last free entry for that. My only concern is when we want to expose another internal dcache data point via > dentry-state, we will have to add one more number to the array which can cause all sort of compatibility problem. So do we want to use the > last free slot for a constant that can be retrieved from somewhere else?
I see no problem in adding more numbers into sysctl. Especially into such rarely used. This interface is designed for that.
Also fields 'age_limit' and 'want_pages' are unused since kernel 2.2.0
> > Cheers, > Longman >
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