[Devel] Re: [PATCH] pid: improved namespaced iteration over processes list

[Sukadev Bhattiprolu]

Dave Hansen [dave at linux.vnet.ibm.com] wrote:
| On Mon, 2008-12-15 at 22:19 +0530, Gowrishankar M wrote:
| > Below patch addresses a common solution for any place where a process
| > should be checked if it is associated to caller namespace. At present,
| > we use 'task_pid_vnr(t) > 0' to further proceed with task 't' in current
| > namespace.
| > 
| > To avoid applying this check in every code related to PID namespace,
| > this patch reworks on iterative macros;for_each_process and do_each_thread.
| > 
| > This patch can also reduce latency time on process list lookup inside the
| > container, as we walk along pidmap, instead of every process in system.

The obvious trade-off is with systems that don't use containers which
are porbably the majority at present. For them next_task() now becomes
more expensive (instead of a simply going to next item on list, they have
lookup in the pidmap, a lookup in  pid hash table followed by mapping the
pid back to task). I think there was a discussion once on this and the
conclusion was things like "kill sig -1" are inherently expensive.

Do you need these to be optimized for containers for some other reason ?

Sukadev
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