Re: [PATCH 2/3] mm: Ensure that mark_page_accessed moves pages tothe active list

From: Rik van Riel
Date: Mon Apr 29 2013 - 13:12:31 EST

On 04/29/2013 12:31 PM, Mel Gorman wrote:

A PageActive page is now added to the inactivate list.

While this looks strange, I think it is sufficiently harmless that additional
barriers to address the case is not justified. Unfortunately, while I never
witnessed it myself, these parallel updates potentially trigger defensive
DEBUG_VM checks on PageActive and hence they are removed by this patch.

Could this not cause issues with __page_cache_release, called from
munmap, exit, truncate, etc.?

Could the eventual skewing of active vs inactive numbers break page
reclaim heuristics?

I wonder if we would need to move to a scheme where the PG_active bit
is always the authoritive one, and we never pass an overriding "lru"
parameter to __pagevec_lru_add.

Would memory ordering between SetPageLRU and testing for PageLRU be
enough to then prevent the statistics from going off?

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