Messages in this thread | | | Subject | Re: [PATCH v8 3/5] ipc: Allow boot time extension of IPCMNI from 32k to 2M | From | Manfred Spraul <> | Date | Tue, 2 Oct 2018 18:32:14 +0200 |
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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 satisfy >>> 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 which >>> 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)? >> >> Thanks, >> Davidlohr > 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 > Solaris.
- I think we should use the same numbers as Solaris. Otherwise we later have to touch it again.
- What is the performance when using shmget() with already 10M segments present?
- I like the new logic for updating the sequence counter.
Is there a reason why you only enable it for extended mode?
You create a rarely used codepath, and I don't understand what speaks against switching to the 'deleted' approach for all systems.
--
Manfred
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