Re: [PATCH] ipc,shm: increase default size for shmmax

[KOSAKI Motohiro]

>> > Hmmm so 0 won't really work because it could be weirdly used to disable
>> > shm altogether... we cannot go to some negative value either since we're
>> > dealing with unsigned, and cutting the range in half could also hurt
>> > users that set the limit above that. So I was thinking of simply setting
>> > SHMMAX to ULONG_MAX and be done with it. Users can then set it manually
>> > if they want a smaller value.
>> >
>> > Makes sense?
>>
>> I don't think people use 0 for disabling. but ULONG_MAX make sense to me too.
>
> Distros could have set it to [U]LONG_MAX in initscripts ten years ago
> - less phone calls, happier customers.  And they could do so today.
>
> But they haven't.   What are the risks of doing this?

I have no idea really. But at least I'm sure current default is much worse.

1. Solaris changed the default to total-memory/4 since Solaris 10 for DB.
 http://www.postgresql.org/docs/9.1/static/kernel-resources.html

2. RHEL changed the default to very big size since RHEL5 (now it is
64GB). Even tough many box don't have 64GB memory at that time.
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