On Fri, May 08, 2020 at 04:00:08PM -0400, Waiman Long wrote: > On 5/8/20 3:38 PM, Konstantin Khlebnikov wrote: > > 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 > > Well, I got rebuke the last time I want to reuse one of age_limit/want_pages > entry for negative dentry count because of the potential of breaking some > really old applications or tools. Changing dentry-state to output one more > number can potentially break compatibility too. That is why I am questioning > if it is a good idea to use up the last free slot. I'd rather see the nr_buckets exposed some other way, leaving this file for dynamic state.
