On Mon, 2010-11-15 at 13:46 -0500, Chris Mason wrote:

Excerpts from Christoph Hellwig's message of 2010-11-15 13:23:14 -0500:

quoted

On Sun, Nov 14, 2010 at 11:12:22PM +0100, Andrea Arcangeli wrote:

quoted

I just wrote above that it can happen upstream without THP. It's not
THP related at all. THP is the consumer, this is a problem in migrate
that will trigger as well with migrate_pages or all other possible
migration APIs.

If more people would be using hugetlbfs they would have noticed
without THP.

Okay, it seems THP is really just the messenger for bad VM practices
here.

quoted

+static int btree_migratepage(struct address_space *mapping,
+                       struct page *newpage, struct page *page)
+{
+       /*
+        * we can't safely write a btree page from here,
+        * we haven't done the locking hook
+        */
+       if (PageDirty(page))
+               return -EAGAIN;

fallback_migrate_page would call writeout() which is apparently not
ok in btrfs for locking issues leading to corruption.

Hmm, it seems the issue for that particular problem is indeedin btrfs.
If it needs external locking for writing out data it should not
implement ->writepage to start with.  Chris, can you explain what's
going on with the btree code? It's pretty funny both in the
btree_writepage which goes directly into extent_write_full_page
if PF_MEMALLOC is not set, but otherwise does much more complicated
work, and also in btree_writepages which skips various WB_SYNC_NONE,
including the very weird check for for_kupdate.

So, I had THP + a patched btrfs running all weekend and I can safely say
I've fixed this one now. 

That seems like good news!

Is that btrfs patch available somewhere?

Where does this leave the existing corrupted btrfs'?

Thanks guys,

Shane

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