From: Waiman Long <email@example.com>
To: Manfred Spraul <firstname.lastname@example.org>,
Davidlohr Bueso <email@example.com>
Cc: "Luis R. Rodriguez" <firstname.lastname@example.org>,
Kees Cook <email@example.com>,
Andrew Morton <firstname.lastname@example.org>,
Jonathan Corbet <email@example.com>,
firstname.lastname@example.org, Al Viro <email@example.com>,
Matthew Wilcox <firstname.lastname@example.org>,
"Eric W. Biederman" <email@example.com>,
Takashi Iwai <firstname.lastname@example.org>, Davidlohr Bueso <email@example.com>
Subject: Re: [PATCH v8 3/5] ipc: Allow boot time extension of IPCMNI from 32k to 2M
Date: Tue, 2 Oct 2018 13:43:13 -0400 [thread overview]
Message-ID: <firstname.lastname@example.org> (raw)
On 10/02/2018 12:32 PM, Manfred Spraul wrote:
> Hello together,
> On 8/18/18 3:15 AM, Waiman Long wrote:
>> On 08/17/2018 12:45 PM, Davidlohr Bueso wrote:
>>> Cc'ing Manfred.
>>> On Mon, 18 Jun 2018, Waiman Long wrote:
>>>> The maximum number of unique System V IPC identifiers was limited to
>>>> 32k. That limit should be big enough for most use cases.
>>>> However, there are some users out there requesting for more. To
>>>> the need of those users, a new boot time kernel option "ipcmni_extend"
>>>> is added to extend the IPCMNI value to 2M. This is a 64X increase
>>>> hopefully is big enough for them.
>>> Could you please provide more info on the need of these users and how
>>> you came up with this new value (which just seems quite arbitrary)?
>> Red Hat has a customer that is migrating from Solaris to Linux. Some of
>> their applications just happen to use more than 32k of shared memory
>> segments. I think Solaris allows up to 16M unique ID.
>> Yes, the amount of increase is a bit arbitrary. I was trying to balance
>> how many bits should be left for sequence number. Maybe I should just
>> take 8 more bits for ID and leave 8 bits for sequence number to match
> - I think we should use the same numbers as Solaris.
> Otherwise we later have to touch it again.
As said in my patch, it is a trade-off between # of uniq identifiers
versus the chance of id reuse. I don't have an objection to increase it
further, but I don't see the customers to really need such a large value.
> - What is the performance when using shmget() with already 10M
> segments present?
I am not sure the performance impact as I had not measure it myself. The
shmget() function is considered in slowpath. We are generally less
concern about its performance than other code paths that are in a
performance critical path.
> - I like the new logic for updating the sequence counter.
> Is there a reason why you only enable it for extended mode?
I tried not to disturb the existing logic for backward compatibility
concern. I don't mind switching it all over to use the new "deleted"
approach if other people have no objection.
> You create a rarely used codepath, and I don't understand what speaks
> against switching to the 'deleted' approach for all systems.
next prev parent reply other threads:[~2018-10-03 0:27 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-06-18 10:28 [PATCH v8 0/5] ipc: IPCMNI limit check for *mni & increase that limit Waiman Long
2018-06-18 10:28 ` [PATCH v8 1/5] ipc: IPCMNI limit check for msgmni and shmmni Waiman Long
2018-06-28 3:16 ` Luis R. Rodriguez
2018-08-17 16:51 ` Davidlohr Bueso
2018-06-18 10:28 ` [PATCH v8 2/5] ipc: IPCMNI limit check for semmni Waiman Long
2018-06-28 22:39 ` Luis R. Rodriguez
2018-06-29 7:26 ` Waiman Long
2018-08-17 16:53 ` Davidlohr Bueso
2018-06-18 10:28 ` [PATCH v8 3/5] ipc: Allow boot time extension of IPCMNI from 32k to 2M Waiman Long
2018-08-17 16:45 ` Davidlohr Bueso
2018-08-18 1:15 ` Waiman Long
2018-10-02 16:32 ` Manfred Spraul
2018-10-02 17:43 ` Waiman Long [this message]
2018-06-18 10:28 ` [PATCH v8 4/5] ipc: Conserve sequence numbers in extended IPCMNI mode Waiman Long
2018-06-18 10:28 ` [PATCH v8 5/5] ipc: Add a new ipcmni_compat sysctl to fall back to old behavior Waiman Long
2018-06-18 11:36 ` kbuild test robot
2018-06-18 14:27 ` kbuild test robot
2018-08-17 16:50 ` [PATCH v8 0/5] ipc: IPCMNI limit check for *mni & increase that limit Davidlohr Bueso
2018-09-06 22:24 ` Andrew Morton
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:
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
* 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).