Re: Control page reclaim granularity

[Minchan Kim <minchan@kernel.org>]

On Mon, Mar 12, 2012 at 10:55:24AM -0400, Rik van Riel wrote:
> On 03/08/2012 04:35 AM, Minchan Kim wrote:
> >On Thu, Mar 08, 2012 at 03:34:13PM +0800, Zheng Liu wrote:
> >>Hi list,
> >>
> >>Recently we encounter a problem about page reclaim.  I abstract it in here.
> >>The problem is that there are two different file types.  One is small index
> >>file, and another is large data file.  The index file is mmaped into memory,
> >>and application hope that they can be kept in memory and don't be reclaimed
> >>too frequently.  The data file is manipulted by read/write, and they should
> >>be reclaimed more frequently than the index file.
> 
> They should indeed be.  The data pages should not get promoted
> to the active list unless they get referenced twice while on
> the inactive list.
> 
> Mmaped pages, on the other hand, get promoted to the active
> list after just one reference.

As I look the code, mmaped page doesn't get promoted by one reference.
It will get promoted by second-round trip or touched by several mapping
when first round trip.

                if (referenced_page || referenced_ptes > 1) 
		        return PAGEREF_ACTIVATE;

> 
> Also, as long as the inactive file list is larger than the
> active file list, we do not reclaim active file pages at
> all.

True.

> 
> >I  think it's a regression since 2.6.28.
> >Before we were trying to keep mapped pages in memory(See calc_reclaim_mapped).
> >But we removed that routine when we applied split lru page replacement.
> >Rik, KOSAKI. What's the rationale?
> 
> One main reason is scalability.  We have to treat pages
> in such a way that we do not have to search through
> gigabytes of memory to find a few eviction candidates
> to place on the inactive list - where they could get
> reused and stopped from eviction again.

Okay. Thanks, Rik.
Then, another question.
Why did we handle mmaped page specially at that time?
Just out of curiosity.

> 
> -- 
> All rights reversed

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