Re: process creation time increases linearly with shmem

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Nick Piggin wrote:
How does the following look? (I changed the comment a bit). Andrew, please
apply if nobody objects.

Nick, I applied this latest patch to a 2.6.12 kernel and found that it does resolve the problem. Prior to the patch on this machine, I was seeing about 23ms spent in fork for ever 100MB of shared memory segment. After applying the patch, fork is taking about 1ms regardless of the shared memory size.

Many thanks to everyone for your help on this.

FWIW, an interesting side effect of this occurs when I run the database with this patch internally on a Linux server that uses NIS. Its an unrelated problem and not a kernel problem. Its due to the children calling initgroups()... apparently when you have many processes making simultaneous initgroups() calls something starts imposing very long waits in increments of 3 seconds, so some processes return from initgroups() in a few ms and other processes complete in 3, 6, 9, up to 21 seconds (plus a few ms). I'm not sure what the story is with that, though its clearly not a kernel issue. If someone happens to have the answer or a suggestion, great, otherwise I'll persue that elsewhere as necessary. (I can reproduce this by simply adding a call to initgroups() call in the child of the forktest program that I sent earlier)


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