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From dean gaudet <>
Subject Re: Linux and Shared Memory.. hell!
Date Mon, 01 May 2000 23:02:57 GMT
any distributor distributing a 2.3/2.4 kernel will mount the shmfs, and
you should consider anyone that hasn't mounted it to be on crack -- you
should always use shm on linux.

in my opinion, applications shouldn't really adapt to "development"
kernels such as the 2.3 series -- as soon as the shmfs thing happenned, it
became a FAQ on linux-kernel, everyone said "apache is broken!" and
everyone else responded "just mount shmfs you dolt".


On Mon, 1 May 2000, Ralf S. Engelschall wrote:

> I'm not a Linux kernel expert, but perhaps someone of us can shed some
> light on me. For MM 1.1.2 I now had to override the Linux decision
> hierarchy for determining the shared memory facility, because
>     1. Linux since many years since to have a broken MMANON support.
>        I never got this running. On a kernel 2.3.99 box it hangs
>        the process and causes a "ps" to hang later, too.
>        This means MM's --with-shm=MMANON cannot be used.
>     2. Linux (kernel 2.0) today showed to dislike even the
>        classic mmap() on /dev/zero variant. It allways returned with
>        EINVAL, independent how I prepare /dev/zero (ftruncate, lseek,
>        write, etc.) or what mapping size I use.
>        This means MM's --with-shm=MMZERO cannot be used.
>     3. Linux (seems like kernel 2.2 or 2.3) requires a shm filesystem to
>        be mounted by the system admin in order to use IPC SHM.
>        This means MM's --with-shm=IPCSHM cannot be used all the time.
>     4. Linux lacks the POSIX shm_open stuff.
>        This means MM's --with-shm=MMPOSX cannot be used at all.
> As a result, it looks like only --with-shm=MMFILE is left for using on
> Linux - which I dislike, because it requires a temporary file. So, can
> this be that the situation is such bad on Linux? Dislikes Linux the way
> MM tries to create the shared memory segments under MMANON and MMZERO or
> why is it failing? Look at mm_core.c if you need details.
>                                        Ralf S. Engelschall

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