kanoj@google.engr.sgi.com (Kanoj Sarcar) writes:
> What you have sent is what I used as a first draft for the implementation.
> The good part of it is that it reduces code duplication. The _really_ bad
> part is that it penalizes users in terms of numbers of shared memory
> segments, max size of /dev/zero mappings, and limitations imposed by
> shm_ctlmax/shm_ctlall/shm_ctlmni etc. I do not think taking up a
> shmid for each /dev/zero mapping is a good idea ...
We can tune all these parameters at runtime. This should not be a
reason.
> Furthermore, I did not want to change behavior of information returned
> by ipc* and various procfs commands, as well as swapout behavior, thus
> the creation of the zmap_list. I decided a few lines of special case
> checking in a handful of places was a much better option.
IMHO all this SYSV ipc stuff is a totally broken API and many agree
with me. I do not care to clutter up the output of it a little bit for
this feature.
Nobody can know who is creating private IPC segments. So nobody should
be irritated by some more segments displayed/used.
In the contrary: I like the ability to restrict the usage of these
segments with the ipc parameters. Keep in mind you can stack a lot of
segments for a DOS attack. and all the segments will use the whole
memory.
> If the current /dev/zero stuff hampers any plans you have with shm code
> (eg page cachification), I would be willing to talk about it ...
It makes shm fs a lot more work. And the special handling slows down
shm handling.
Greetings
Christoph
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