Re: [PATCH -mm] vmscan: protect a fraction of file backed mappedpages from reclaim

[Rik van Riel]

Christoph Lameter wrote:
> On Tue, 12 May 2009, Rik van Riel wrote:
>
> > The patch that only allows active file pages to be deactivated
> > if the active file LRU is larger than the inactive file LRU should
> > protect the working set from being evicted due to streaming IO.
>
> Streaming I/O means access once? 

Yeah, "used-once pages" would be a better criteria, since
you could go through a gigantic set of used-once pages without
doing linear IO.

I expect that some databases might do that.

> What exactly are the criteria for a page
> to be part of streaming I/O? AFAICT the definition is more dependent on
> the software running than on a certain usage pattern discernible to the
> VM. Software may after all perform multiple scans over a stream of data or
> go back to prior locations in the file.


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