Messages in this thread | | | Date | Fri, 14 Oct 2022 13:11:54 +0100 | From | Matthew Wilcox <> | Subject | Re: [RFC PATCH] mm: move xa forward when run across zombie page |
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On Fri, Oct 14, 2022 at 01:30:48PM +0800, zhaoyang.huang wrote: > From: Zhaoyang Huang <zhaoyang.huang@unisoc.com> > > Bellowing RCU stall is reported where kswapd traps in a live lock when shrink > superblock's inode list. The direct reason is zombie page keeps staying on the > xarray's slot and make the check and retry loop permanently. The root cause is unknown yet > and supposed could be an xa update without synchronize_rcu etc. I would like to > suggest skip this page to break the live lock as a workaround.
No, the underlying bug should be fixed.
> if (!folio || xa_is_value(folio)) > return folio; > > - if (!folio_try_get_rcu(folio)) > + if (!folio_try_get_rcu(folio)) { > + xas_advance(xas, folio->index + folio_nr_pages(folio) - 1); > goto reset; > + }
You can't do this anyway. To call folio_nr_pages() and to look at folio->index, you must have a refcount on the page, and this is the path where we failed to get the refcount.
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