Re: 2.6.26-rc5-mm2: OOM with 1G free swap

Nick Piggin
2008-06-11T13:44:48Z

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On Wednesday 11 June 2008 22:57, Rik van Riel wrote:
> On Tue, 10 Jun 2008 23:27:05 -0700
>
> Andrew Morton <akpm@linux-foundation.org> wrote:
> > Well I assume that Rik ran LTP. Perhaps a merge problem.
> >
> > Zero pages on active_anon and inactive_anon. I suspect we lost those
> > pages.
>
> Known problem. I fixed this one in the updates I sent you last night.

Oh good. Yeah I was just running some tests, and got as far as verifying
that the upstream kernel + lockless pagecache patches reclaims file pages
like a dream, but -mm2 sucks very badly at it.

During which, I also did find by inspection a little problem with my
speculative references patch. Andrew please apply this fix.

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Fix the VM_BUG_ON assertion check to actually do what I want, noted by
Christoph.

Also, fix an error-path-leak type issue with frozen refcount not being
unfrozen. Found by review. In practice, this check is very rare to hit
because a page dirtier is likely to hold the refcount elevated for much
longer than it takes to check and non-racy-recheck. So it doesn't pose
a big problem for users of -mm, but of course needs fixing.

---
Index: linux-2.6/mm/vmscan.c
===================================================================
--- linux-2.6.orig/mm/vmscan.c 2008-06-11 23:36:07.000000000 +1000
+++ linux-2.6/mm/vmscan.c 2008-06-11 23:36:18.000000000 +1000
@@ -415,8 +415,10 @@ static int __remove_mapping(struct addre
if (!page_freeze_refs(page, 2))
goto cannot_free;
/* note: atomic_cmpxchg in page_freeze_refs provides the smp_rmb */
- if (unlikely(PageDirty(page)))
+ if (unlikely(PageDirty(page))) {
+ page_unfreeze_refs(page, 2);
goto cannot_free;
+ }

if (PageSwapCache(page)) {
swp_entry_t swap = { .val = page_private(page) };
Index: linux-2.6/include/linux/pagemap.h
===================================================================
--- linux-2.6.orig/include/linux/pagemap.h 2008-06-11 23:36:07.000000000 +1000
+++ linux-2.6/include/linux/pagemap.h 2008-06-11 23:36:18.000000000 +1000
@@ -165,7 +165,7 @@ static inline int page_cache_get_specula
return 0;
}
#endif
- VM_BUG_ON(PageCompound(page) && (struct page *)page_private(page) != page);
+ VM_BUG_ON(PageTail(page));

return 1;
}