Messages in this thread | | | Date | Fri, 21 May 2010 13:31:36 -0700 | From | Andrew Morton <> | Subject | Re: [patch 3/3] ipc: increase IPCMNI_MAX |
| |
On Thu, 20 May 2010 17:07:41 +1000 Nick Piggin <npiggin@suse.de> wrote:
> Just wondering whether there is a good reason to have a full 16 bits of > sequence in ipc ids? 32K indexes is pretty easy to overflow, if only in > stress tests for now. I was doing some big aim7 stress testing, which > required this patch, but it's not exactly a realistic workload :) > > But the sequence seems like it just helps slightly with buggy apps, and > if the app is buggy then it can by definition mess up its own ids > anyway? So I don't see that such amount of seq is required. > > Index: linux-2.6/ipc/util.h > =================================================================== > --- linux-2.6.orig/ipc/util.h > +++ linux-2.6/ipc/util.h > @@ -14,7 +14,16 @@ > #include <linux/err.h> > > /* IPCMNI_MAX should be <= MAX_INT, absolute limit for ipc arrays */ > -#define IPCMNI_MAX_SHIFT 15 > +/* > + * IPC ids consist of an index into the idr, which allocates from the bottom > + * up, and a sequence number which is continually incremented. Valid indexes > + * are from 0..IPCMNI_MAX (or further constrained by sysctls or other limits). > + * The sequence number prevents ids from being reused quickly. The sequence > + * number resides in the top part of the 'int' after IPCMNI_MAX. > + * > + * Increasing IPCMNI_MAX reduces the sequence wrap interval. > + */ > +#define IPCMNI_MAX_SHIFT 20 > #define IPCMNI_MAX (1 << IPCMNI_MAX_SHIFT) > > #define SEQ_SHIFT IPCMNI_MAX_SHIFT
Some anaylsis of the worst-case memory consumption would be mollifying.
I took the absence of Signed-off-by:'s to mean "rfc" and wandered away.
| |