Remember that ironic get_user_pages race? when the raised page_count on a
page swapped out led do_wp_page to decide that it had to copy on write, so
substituted a different page into userspace. 2.6.7 onwards have Andrea's
solution, where try_to_unmap_one backs out if it finds page_count raised.
Which works, but is unsatisfying (rmap.c has no other page_count heuristics),
and was found a few months ago to hang an intensive page migration test. A
year ago I was hesitant to engage page_mapcount, now it seems the right fix.
So remove the page_count hack from try_to_unmap_one; and use activate_page in
unuse_mm when dropping lock, to replace its secondary effect of helping
swapoff to make progress in that case.
Simplify can_share_swap_page (now called only on anonymous pages) to check
page_mapcount + page_swapcount == 1: still needs the page lock to stabilize
their (pessimistic) sum, but does not need swapper_space.tree_lock for that.
In do_swap_page, move swap_free and unlock_page below page_add_anon_rmap, to
keep sum on the high side, and correct when can_share_swap_page called.
Signed-off-by: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
try_to_unmap_cluster() does:
for (pte = pte_offset_map(pmd, address);
address < end; pte++, address += PAGE_SIZE) {
...
}
pte_unmap(pte);
It may take a little staring to notice, but pte can actually fall off the
end of the pte page in this iteration, which makes life difficult for
kmap_atomic() and the users not expecting it to BUG(). Of course, we're
somewhat lucky in that arithmetic elsewhere in the function guarantees that
at least one iteration is made, lest this force larger rearrangements to be
made. This issue and patch also apply to non-mm mainline and with trivial
adjustments, at least two related kernels.
Discovered during internal testing at Oracle.
Signed-off-by: William Irwin <wli@holomorphy.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
This patch fixes a bug introduced by the "mm counter operations through
macros" patch, which replaced a decrement operation in with an increment
macro in try_to_unmap_one().
Signed-off-by: Björn Steinbrink <B.Steinbrink@gmx.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
mm/rmap.c:page_referenced_one() and mm/rmap.c:try_to_unmap_one() contain
identical code that
- takes mm->page_table_lock;
- drills through page tables;
- checks that correct pte is reached.
Coalesce this into page_check_address()
Signed-off-by: Nikita Danilov <nikita@clusterfs.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>
Initial git repository build. I'm not bothering with the full history,
even though we have it. We can create a separate "historical" git
archive of that later if we want to, and in the meantime it's about
3.2GB when imported into git - space that would just make the early
git days unnecessarily complicated, when we don't have a lot of good
infrastructure for it.
Let it rip!
Hugh Dickins