Re: hunting an IO hang

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

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>

Thanks, Andrea.

-- 
Kind regards,
Minchan Kim

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