Re: hunting an IO hang

[Minchan Kim <minchan.kim@gmail.com>]

On Mon, Jan 17, 2011 at 11:47:46PM +0900, Minchan Kim wrote:
> On Mon, Jan 17, 2011 at 03:26:15PM +0100, Andrea Arcangeli wrote:
> > On Mon, Jan 17, 2011 at 09:10:15AM -0500, Chris Mason wrote:
> > > Excerpts from Andrea Arcangeli's message of 2011-01-17 00:11:35 -0500:
> > > 
> > > [ crashes under load ]
> > > 
> > > > 
> > > > NOTE: with the last changes compaction is used for all order > 0 and
> > > > even from kswapd, so you will now be able to trigger bugs in
> > > > compaction or migration even with THP off. However I'm surprised that
> > > > you have issues with compaction...
> > > 
> > > I know I mentioned this in another email, but it is kind of buried in
> > > other context.  I reproduced my crash with CONFIG_COMPACTION and
> > > CONFIG_MIGRATION off.
> > 
> > Ok, then it was an accident the page->lru got corrupted during
> > migration and it has nothing to do with migration/compaction/thp. This
> > makes sense because we should have noticed long ago if something
> > wasn't stable there.
> > 
> > I reworked the fix for the two memleaks I found while reviewing
> > migration code for this bug (unrelated) introduced by the commit
> > cf608ac19c95804dc2df43b1f4f9e068aa9034ab. It was enough to move the
> > goto to fix this without having to add a new function (it's
> > functionally identical to the one I sent before). It also wouldn't
> > leak memory if it was compaction invoking migrate_pages (only other
> > callers checking the retval of migrate_pages instead of list_empty,
> > could leak memory). As said before, this couldn't explain your
> > problem, and this is only a code review fix, I never triggered this.
> > 
> > This is still only for review for Minchan, not meant for inclusion
> > yet.
> > 
> > ===
> > Subject: when migrate_pages returns 0, all pages must have been released
> > 
> > From: Andrea Arcangeli <aarcange@redhat.com>
> > 
> > In some cases migrate_pages could return zero while still leaving a
> > few pages in the pagelist (and some caller wouldn't notice it has to
> > call putback_lru_pages after commit
> > cf608ac19c95804dc2df43b1f4f9e068aa9034ab).
> > 
> > Add one missing putback_lru_pages not added by commit
> > cf608ac19c95804dc2df43b1f4f9e068aa9034ab.
> 
> It would be better to have another patch.
> 
> > 
> > Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
> Reviewed-by: Minchan Kim <minchan.kim@gmail.com>

And don't we need this patch, either?