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SubjectRe: [patch -mm] cpusets: add memory_slab_hardwall flag
On Mon, 9 Mar 2009, Christoph Lameter wrote:

> Again these are fastpath modifications.
>

The nature of the change requires the logic to be placed in the fastpath
to determine whether a cpu slab's node is allowed by the allocating task's
cpuset.

You have previously stated that you would prefer that this feature be
tunable from userspace. This patch adds the `memory_slab_hardwall' cpuset
flag which defaults to off.

> Scanning the partial list for matching nodes is an expensive operation.
>

It depends on how long you scan for a matching node, but again: this
should be assumed by the user if the option has been enabled.

> Adding RCU into the fast paths is also another big worry.
>

This could be mitigated by adding a PF_SLAB_HARDWALL flag similiar to
PF_SPREAD_PAGE and PF_SPREAD_SLAB. I'd prefer not to add additional
cpuset-specific task flags, but this would address your concern.


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