Messages in this thread | | | Date | Thu, 8 Apr 2021 17:18:41 +0100 | From | Chris Down <> | Subject | Re: [PATCH] mm: page_counter: mitigate consequences of a page_counter underflow |
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Johannes Weiner writes: >When the unsigned page_counter underflows, even just by a few pages, a >cgroup will not be able to run anything afterwards and trigger the OOM >killer in a loop. > >Underflows shouldn't happen, but when they do in practice, we may just >be off by a small amount that doesn't interfere with the normal >operation - consequences don't need to be that dire. > >Reset the page_counter to 0 upon underflow. We'll issue a warning that >the accounting will be off and then try to keep limping along. > >[ We used to do this with the original res_counter, where it was a > more straight-forward correction inside the spinlock section. I > didn't carry it forward into the lockless page counters for > simplicity, but it turns out this is quite useful in practice. ] > >Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Acked-by: Chris Down <chris@chrisdown.name>
>--- > mm/page_counter.c | 8 ++++++-- > 1 file changed, 6 insertions(+), 2 deletions(-) > >diff --git a/mm/page_counter.c b/mm/page_counter.c >index c6860f51b6c6..7d83641eb86b 100644 >--- a/mm/page_counter.c >+++ b/mm/page_counter.c >@@ -52,9 +52,13 @@ void page_counter_cancel(struct page_counter *counter, unsigned long nr_pages) > long new; > > new = atomic_long_sub_return(nr_pages, &counter->usage); >- propagate_protected_usage(counter, new); > /* More uncharges than charges? */ >- WARN_ON_ONCE(new < 0); >+ if (WARN_ONCE(new < 0, "page_counter underflow: %ld nr_pages=%lu\n", >+ new, nr_pages)) { >+ new = 0; >+ atomic_long_set(&counter->usage, new); >+ } >+ propagate_protected_usage(counter, new); > } > > /** >-- >2.31.1 > >
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