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

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



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.

Cheers,
Longman







[Index of Archives]     [Linux ARM Kernel]     [Linux ARM]     [Linux Omap]     [Fedora ARM]     [IETF Annouce]     [Bugtraq]     [Linux OMAP]     [Linux MIPS]     [eCos]     [Asterisk Internet PBX]     [Linux API]

  Powered by Linux