Re: [PATCH/RFC 0/4] VM: Manual and Automatic page cache reclaim

[Andrew Morton <akpm@osdl.org>]

Martin Hicks <mort@sgi.com> wrote:
>
> The patches introduce two different ways to free up page cache from a
>  node: manually through a syscall and automatically through flag
>  modifiers to a mempolicy.

Backing up and thinking about this a bit more....

>  Currently if a job is started and there is page cache lying around on a
>  particular node then allocations will spill onto remote nodes and page
>  cache won't be reclaimed until the whole system is short on memory.
>  This can result in a signficiant performance hit for HPC applications
>  that planned on that memory being allocated locally.

Why do it this way at all?

Is it not possible to change the page allocator's zone fallback mechanism
so that once the local node's zones' pages are all allocated, we don't
simply advance onto the next node?  Instead, could we not perform a bit of
reclaim on this node's zones first?  Only advance onto the next nodes if
things aren't working out?
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