Re: [PATCH 1/3] mm: page allocator: Update free page counters after pages are placed on the free list

[Minchan Kim <minchan.kim@gmail.com>]

On Tue, Aug 17, 2010 at 10:59:18AM +0100, Mel Gorman wrote:
> On Tue, Aug 17, 2010 at 11:21:15AM +0900, Minchan Kim wrote:
> > Now allocation path decrease NR_FREE_PAGES _after_ it remove pages from buddy.
> > It can make that actually we don't have enough pages in buddy but
> > pretend to have enough pages.
> > It could make same situation with free path which is your concern.
> > So I think it can confuse watermark check in extreme case.
> > 
> > So don't we need to consider _allocation_ path with conservative?
> > 
> 
> I considered it and it would be desirable. The downside was that the
> paths became more complicated. Take rmqueue_bulk() for example. It could
> start by modifying the counters but there then needs to be a recovery
> path if all the requested pages were not allocated.
> 
> It'd be nice to see if these patches on their own were enough to
> alleviate the worst of the per-cpu-counter drift before adding new
> branches to the allocation path.
> 
> Does that make sense?

No problem. It was a usecase of big machine. 
I also hope we don't add unnecessary overhead in normal machine due to unlikely problem.
Let's consider it by further step if it isn't enough.

Thanks, Mel.

> 
> -- 
> Mel Gorman
> Part-time Phd Student                          Linux Technology Center
> University of Limerick                         IBM Dublin Software Lab

-- 
Kind regards,
Minchan Kim

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