From: Waiman Long <longman@redhat.com>
To: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>,
linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org,
linux-mm@kvack.org, Alexander Viro <viro@zeniv.linux.org.uk>
Subject: Re: [PATCH RFC 1/8] dcache: show count of hash buckets in sysctl fs.dentry-state
Date: Fri, 8 May 2020 16:00:08 -0400 [thread overview]
Message-ID: <34ed1b12-1bee-8158-3084-fb1059b6686a@redhat.com> (raw)
In-Reply-To: <1f137f70-3d37-eb70-2e85-2541e504afbd@yandex-team.ru>
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
next prev parent reply other threads:[~2020-05-08 20:00 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-08 12:23 [PATCH RFC 0/8] dcache: increase poison resistance Konstantin Khlebnikov
2020-05-08 12:23 ` [PATCH RFC 1/8] dcache: show count of hash buckets in sysctl fs.dentry-state Konstantin Khlebnikov
2020-05-08 14:49 ` Waiman Long
2020-05-08 16:16 ` Konstantin Khlebnikov
2020-05-08 19:05 ` Waiman Long
2020-05-08 19:38 ` Konstantin Khlebnikov
2020-05-08 20:00 ` Waiman Long [this message]
2020-05-08 20:03 ` Matthew Wilcox
2020-05-08 12:23 ` [PATCH RFC 2/8] selftests: add stress testing tool for dcache Konstantin Khlebnikov
2020-05-13 1:52 ` Dave Chinner
2020-05-08 12:23 ` [PATCH RFC 3/8] dcache: sweep cached negative dentries to the end of list of siblings Konstantin Khlebnikov
2020-05-08 19:38 ` Waiman Long
2020-05-08 12:23 ` [PATCH RFC 4/8] fsnotify: stop walking child dentries if remaining tail is negative Konstantin Khlebnikov
2020-05-08 12:23 ` [PATCH RFC 5/8] dcache: add action D_WALK_SKIP_SIBLINGS to d_walk() Konstantin Khlebnikov
2020-05-08 12:23 ` [PATCH RFC 6/8] dcache: stop walking siblings if remaining dentries all negative Konstantin Khlebnikov
2020-05-08 12:23 ` [PATCH RFC 7/8] dcache: push releasing dentry lock into sweep_negative Konstantin Khlebnikov
2020-05-08 12:23 ` [PATCH RFC 8/8] dcache: prevent flooding with negative dentries Konstantin Khlebnikov
2020-05-08 14:56 ` Matthew Wilcox
2020-05-08 16:29 ` Konstantin Khlebnikov
2020-05-08 21:07 ` Waiman Long
2020-12-09 23:01 ` [PATCH RFC 0/8] dcache: increase poison resistance Junxiao Bi
[not found] ` <CALYGNiN2F8gcKX+2nKOi1tapquJWfyzUkajWxTqgd9xvd7u1AA@mail.gmail.com>
2020-12-13 18:49 ` Junxiao Bi
[not found] ` <CALYGNiM8Fp=ZV8S6c2L50ne1cGhE30PrT-C=4nfershvfAgP+Q@mail.gmail.com>
2020-12-14 23:10 ` Junxiao Bi
2020-12-16 18:46 ` Junxiao Bi
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=34ed1b12-1bee-8158-3084-fb1059b6686a@redhat.com \
--to=longman@redhat.com \
--cc=khlebnikov@yandex-team.ru \
--cc=linux-fsdevel@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-mm@kvack.org \
--cc=viro@zeniv.linux.org.uk \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).