On Wed, 31 Oct 2012, Hugh Dickins wrote:
> On Wed, 31 Oct 2012, Zhouping Liu wrote:
> > On 10/31/2012 03:26 PM, Hugh Dickins wrote:
> > >
> > > There's quite a few put_page()s in do_huge_pmd_numa_page(), and it
> > > would help if we could focus on the one which is giving the trouble,
> > > but I don't know which that is. Zhouping, if you can, please would
> > > you do an "objdump -ld vmlinux >bigfile" of your kernel, then extract
> > > from bigfile just the lines from "<do_huge_pmd_numa_page>:" to whatever
> > > is the next function, and post or mail privately just that disassembly.
> > > That should be good to identify which of the put_page()s is involved.
> >
> > Hugh, I didn't find the next function, as I can't find any words that matched
> > "do_huge_pmd_numa_page".
> > is there any other methods?
>
> Hmm, do_huge_pmd_numa_page does appear in your stacktrace,
> unless I've made a typo but am blind to it.
>
> Were you applying objdump to the vmlinux which gave you the
> BUG at mm/memcontrol.c:1134! ?
Thanks for the further info you then sent privately: I have not made any
more effort to reproduce the issue, but your objdump did tell me that the
put_page hitting the problem is the one on line 872 of mm/huge_memory.c,
"Drop the local reference", just before successful return after migration.
I didn't really get the inspiration I'd hoped for out of knowing that,
but it did make wonder whether you're suffering from one of the issues
I already mentioned, and I can now see a way in which it might cause
the mm/memcontrol.c:1134 BUG:-
migrate_page_copy() does TestClearPageActive on the source page:
so given the unsafe way in which do_huge_pmd_numa_page() was proceeding
with a !PageLRU page, it's quite possible that the page was sitting in
a pagevec, and added to the active lru (so added to the lru_size of the
active lru), but our final put_page removes it from lru, active flag has
been cleared, so we subtract it from the lru_size of the inactive lru -
that could indeed make it go negative and trigger the BUG.
Here's a patch fixing and tidying up that and a few other things there.
But I'm not signing it off yet, partly because I've barely tested it
(quite probably I didn't even have any numa pmd migration happening
at all), and partly because just a moment ago I ran across this
instructive comment in __collapse_huge_page_isolate():
/* cannot use mapcount: can't collapse if there's a gup pin */
if (page_count(page) != 1) {
Hmm, yes, below I've added the page_mapcount() check I proposed to
do_huge_pmd_numa_page(), but is even that safe enough? Do we actually
need a page_count() check (for 2?) to guard against get_user_pages()?
I suspect we do, but then do we have enough locking to stabilize such
a check? Probably, but...
This will take more time, and I doubt get_user_pages() is an issue in
your testing, so please would you try the patch below, to see if it
does fix the BUGs you are seeing? Thanks a lot.
Not-Yet-Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx>
---
mm/huge_memory.c | 24 +++++++++---------------
1 file changed, 9 insertions(+), 15 deletions(-)
--- 3.7-rc2+schednuma+johannes/mm/huge_memory.c 2012-11-01 04:10:43.812155671 -0700
+++ linux/mm/huge_memory.c 2012-11-01 05:52:19.512153771 -0700
@@ -745,7 +745,7 @@ void do_huge_pmd_numa_page(struct mm_str
struct mem_cgroup *memcg = NULL;
struct page *new_page = NULL;
struct page *page = NULL;
- int node, lru;
+ int node = -1;
spin_lock(&mm->page_table_lock);
if (unlikely(!pmd_same(*pmd, entry)))
@@ -762,7 +762,8 @@ void do_huge_pmd_numa_page(struct mm_str
VM_BUG_ON(!PageCompound(page) || !PageHead(page));
get_page(page);
- node = mpol_misplaced(page, vma, haddr);
+ if (page_mapcount(page) == 1) /* Only do exclusively mapped */
+ node = mpol_misplaced(page, vma, haddr);
if (node != -1)
goto migrate;
}
@@ -801,13 +802,11 @@ migrate:
if (!new_page)
goto alloc_fail;
- lru = PageLRU(page);
-
- if (lru && isolate_lru_page(page)) /* does an implicit get_page() */
+ if (isolate_lru_page(page)) /* Does an implicit get_page() */
goto alloc_fail;
- if (!trylock_page(new_page))
- BUG();
+ __set_page_locked(new_page);
+ SetPageSwapBacked(new_page);
/* anon mapping, we can simply copy page->mapping to the new page: */
new_page->mapping = page->mapping;
@@ -820,8 +819,6 @@ migrate:
spin_lock(&mm->page_table_lock);
if (unlikely(!pmd_same(*pmd, entry))) {
spin_unlock(&mm->page_table_lock);
- if (lru)
- putback_lru_page(page);
unlock_page(new_page);
ClearPageActive(new_page); /* Set by migrate_page_copy() */
@@ -829,6 +826,7 @@ migrate:
put_page(new_page); /* Free it */
unlock_page(page);
+ putback_lru_page(page);
put_page(page); /* Drop the local reference */
return;
@@ -859,16 +857,12 @@ migrate:
mem_cgroup_end_migration(memcg, page, new_page, true);
spin_unlock(&mm->page_table_lock);
- put_page(page); /* Drop the rmap reference */
-
task_numa_fault(node, HPAGE_PMD_NR);
- if (lru)
- put_page(page); /* drop the LRU isolation reference */
-
unlock_page(new_page);
-
unlock_page(page);
+ put_page(page); /* Drop the rmap reference */
+ put_page(page); /* Drop the LRU isolation reference */
put_page(page); /* Drop the local reference */
return;
--
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