mm: don't mark_page_accessed in fault path
Doing a mark_page_accessed at fault-time, then doing SetPageReferenced at unmap-time if the pte is young has a number of problems. mark_page_accessed is supposed to be roughly the equivalent of a young pte for unmapped references. Unfortunately it doesn't come with any context: after being called, reclaim doesn't know who or why the page was touched. So calling mark_page_accessed not only adds extra lru or PG_referenced manipulations for pages that are already going to have pte_young ptes anyway, but it also adds these references which are difficult to work with from the context of vma specific references (eg. MADV_SEQUENTIAL pte_young may not wish to contribute to the page being referenced). Then, simply doing SetPageReferenced when zapping a pte and finding it is young, is not a really good solution either. SetPageReferenced does not correctly promote the page to the active list for example. So after removing mark_page_accessed from the fault path, several mmap()+touch+munmap() would have a very different result from several read(2) calls for example, which is not really desirable. Signed-off-by:Nick Piggin <npiggin@suse.de> Acked-by:
Johannes Weiner <hannes@saeurebad.de> Signed-off-by:
Andrew Morton <akpm@linux-foundation.org> Signed-off-by:
Linus Torvalds <torvalds@linux-foundation.org>
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3340289d
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