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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@ -1530,7 +1530,6 @@ retry_find:
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/*
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/*
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* Found the page and have a reference on it.
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* Found the page and have a reference on it.
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*/
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*/
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mark_page_accessed(page);
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ra->prev_pos = (loff_t)page->index << PAGE_CACHE_SHIFT;
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ra->prev_pos = (loff_t)page->index << PAGE_CACHE_SHIFT;
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vmf->page = page;
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vmf->page = page;
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return ret | VM_FAULT_LOCKED;
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return ret | VM_FAULT_LOCKED;
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@ -768,7 +768,7 @@ static unsigned long zap_pte_range(struct mmu_gather *tlb,
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if (pte_dirty(ptent))
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if (pte_dirty(ptent))
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set_page_dirty(page);
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set_page_dirty(page);
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if (pte_young(ptent))
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if (pte_young(ptent))
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SetPageReferenced(page);
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mark_page_accessed(page);
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file_rss--;
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file_rss--;
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}
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}
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page_remove_rmap(page, vma);
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page_remove_rmap(page, vma);
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