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Date: Fri, 8 May 2020 15:05:18 -0400 From: Waiman Long <longman@...hat.com> To: Konstantin Khlebnikov <khlebnikov@...dex-team.ru>, linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org, linux-mm@...ck.org, Alexander Viro <viro@...iv.linux.org.uk> Subject: Re: [PATCH RFC 1/8] dcache: show count of hash buckets in sysctl fs.dentry-state 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? Cheers, Longman
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