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

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(2014/04/02 4:19), Andrew Morton wrote:
On Tue, 01 Apr 2014 15:29:05 +0900 Kamezawa Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> wrote:


So their system will act as if they had set SHMMAX=enormous.  What
problems could that cause?


Look.  The 32M thing is causing problems.  Arbitrarily increasing the
arbitrary 32M to an arbitrary 128M won't fix anything - we still have
the problem.  Think bigger, please: how can we make this problem go
away for ever?


Our middleware engineers has been complaining about this sysctl limit.
System administrator need to calculate required sysctl value by making sum
of all planned middlewares, and middleware provider needs to write "please
calculate systcl param by....." in their installation manuals.

Why aren't people just setting the sysctl to a petabyte?  What problems
would that lead to?


They(and admin) don't know the fact, setting petabytes won't cause any pain.

In their thinking:
==
If there is a kernel's limit, it should have some (bad) side-effect and
the trade-off which must be handled by admin is represented by the limit.
In this case, they think setting this value large will consume tons of resource.
==
They don't care kernel's implemenation but takes care of what API says.

Of course, always I was asked, I answer set it to peta-bytes. But the fact
*default is small* makes them doubtful.

Thanks,
-Kame

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