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

[Nick Piggin <nickpiggin@yahoo.com.au>]

Andrew Morton wrote:
> 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?

Yeah. I got a patch that does this. It is quite possible - you have
to make some balance so you don't go to shit on workloads that have
a working set larger than a single node's memory, but...

-- 
SUSE Labs, Novell Inc.

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