The patch titled
mm: don't mark_page_accessed in fault path
has been added to the -mm tree. Its filename is
mm-dont-mark_page_accessed-in-fault-path.patch
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Subject: mm: don't mark_page_accessed in fault path
From: Nick Piggin <npiggin@xxxxxxx>
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@xxxxxxx>
Acked-by: Johannes Weiner <hannes@xxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/filemap.c | 1 -
mm/memory.c | 2 +-
2 files changed, 1 insertion(+), 2 deletions(-)
diff -puN mm/filemap.c~mm-dont-mark_page_accessed-in-fault-path mm/filemap.c
--- a/mm/filemap.c~mm-dont-mark_page_accessed-in-fault-path
+++ a/mm/filemap.c
@@ -1530,7 +1530,6 @@ retry_find:
/*
* 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;
diff -puN mm/memory.c~mm-dont-mark_page_accessed-in-fault-path mm/memory.c
--- a/mm/memory.c~mm-dont-mark_page_accessed-in-fault-path
+++ a/mm/memory.c
@@ -760,7 +760,7 @@ static unsigned long zap_pte_range(struc
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);
_
Patches currently in -mm which might be from npiggin@xxxxxxx are
origin.patch
mm-increase-the-default-mlock-limit-from-32k-to-64k.patch
fs-remove-prepare_write-commit_write.patch
linux-next.patch
mm-dont-mark_page_accessed-in-fault-path.patch
reiser4.patch
likeliness-accounting-change-and-cleanup.patch
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