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mm: don't mark_page_accessed in fault path

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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>
This commit is contained in:
Nick Piggin 2009-01-06 14:38:55 -08:00 committed by Linus Torvalds
parent 3340289ddf
commit bf3f3bc5e7
2 changed files with 1 additions and 2 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

1
mm/filemap.c
View file

@ -1530,7 +1530,6 @@ int filemap_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
/*
* Found the page and have a reference on it.
*/
mark_page_accessed(page);
ra->prev_pos = (loff_t)page->index << PAGE_CACHE_SHIFT;
vmf->page = page;
return ret | VM_FAULT_LOCKED;

2
mm/memory.c
View file

@ -768,7 +768,7 @@ static unsigned long zap_pte_range(struct mmu_gather *tlb,
if (pte_dirty(ptent))
set_page_dirty(page);
if (pte_young(ptent))
SetPageReferenced(page);
mark_page_accessed(page);
file_rss--;
}
page_remove_rmap(page, vma);