Re: [PATCH 1/3] HWPOISON: fix action_result() to print out dirty/clean

Naoya Horiguchi
2012-08-23T20:31:24Z

Hello,

Thank you for your review.

On Thu, Aug 23, 2012 at 05:33:30PM +0800, Fengguang Wu wrote:
> On Wed, Aug 22, 2012 at 11:17:33AM -0400, Naoya Horiguchi wrote:
> > action_result() fails to print out "dirty" even if an error occurred on a
> > dirty pagecache, because when we check PageDirty in action_result() it was
> > cleared after page isolation even if it's dirty before error handling. This
> > can break some applications that monitor this message, so should be fixed.
> >
> > There are several callers of action_result() except page_action(), but
> > either of them are not for LRU pages but for free pages or kernel pages,
> > so we don't have to consider dirty or not for them.
> >
> > Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
> > Reviewed-by: Andi Kleen <ak@linux.intel.com>
> > ---
> > mm/memory-failure.c | 22 +++++++++-------------
> > 1 file changed, 9 insertions(+), 13 deletions(-)
> >
> > diff --git v3.6-rc1.orig/mm/memory-failure.c v3.6-rc1/mm/memory-failure.c
> > index a6e2141..79dfb2f 100644
> > --- v3.6-rc1.orig/mm/memory-failure.c
> > +++ v3.6-rc1/mm/memory-failure.c
> > @@ -779,16 +779,16 @@ static struct page_state {
> > { compound, compound, "huge", me_huge_page },
> > #endif
> >
> > - { sc|dirty, sc|dirty, "swapcache", me_swapcache_dirty },
> > - { sc|dirty, sc, "swapcache", me_swapcache_clean },
> > + { sc|dirty, sc|dirty, "dirty swapcache", me_swapcache_dirty },
> > + { sc|dirty, sc, "clean swapcache", me_swapcache_clean },
> >
> > - { unevict|dirty, unevict|dirty, "unevictable LRU", me_pagecache_dirty},
> > - { unevict, unevict, "unevictable LRU", me_pagecache_clean},
> > + { unevict|dirty, unevict|dirty, "dirty unevictable LRU", me_pagecache_dirty },
> > + { unevict, unevict, "clean unevictable LRU", me_pagecache_clean },
> >
> > - { mlock|dirty, mlock|dirty, "mlocked LRU", me_pagecache_dirty },
> > - { mlock, mlock, "mlocked LRU", me_pagecache_clean },
> > + { mlock|dirty, mlock|dirty, "dirty mlocked LRU", me_pagecache_dirty },
> > + { mlock, mlock, "clean mlocked LRU", me_pagecache_clean },
> >
> > - { lru|dirty, lru|dirty, "LRU", me_pagecache_dirty },
> > + { lru|dirty, lru|dirty, "dirty LRU", me_pagecache_dirty },
> > { lru|dirty, lru, "clean LRU", me_pagecache_clean },
>
> According to the set_page_dirty() comment, the dirty bit might be set
> outside the page lock (however I don't know any concrete examples).
> That means the word "clean" is not 100% right. That's probably why we
> only report "dirty LRU" and didn't say "clean LRU".

So this doesn't seem to be just a messaging problem. If PageDirty is set
outside page lock, we can handle the dirty page only with me_pagecache_clean(),
without me_pagecache_dirty().
It might be a good idea to add some check code to detect such kind of race
and give up error isolation if it does.
I'll dig into who sets dirty flags outside/inside page locks, and look for
a workaround. (But it will be in another patch...)

Thanks,
Naoya