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.
>
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