linux-kernel - Re: [PATCH RFC 1/8] dcache: show count of hash buckets in sysctl fs.dentry-state

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Date:   Fri, 8 May 2020 19:16:40 +0300
From:   Konstantin Khlebnikov <khlebnikov@...dex-team.ru>
To:     Waiman Long <longman@...hat.com>, 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 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.

> 
> Cheers,
> Longman
>