Re: [Bug 42578] Kernel crash "Out of memory error by X" when using NTFS file system on external USB Hard drive

[Andrew Morton <akpm@linux-foundation.org>]

(switched to email.  Please respond via emailed reply-to-all, not via the
bugzilla web interface).

On Wed, 18 Jan 2012 09:22:12 GMT
bugzilla-daemon@bugzilla.kernel.org wrote:

> https://bugzilla.kernel.org/show_bug.cgi?id=42578

Stuart has an 8GB x86_32 machine.  It has large amounts of NTFS
pagecache in highmem.  NTFS is using 512-byte buffer_heads.  All of the
machine's lowmem is being consumed by struct buffer_heads which are
attached to the highmem pagecache and the machine is dead in the water,
getting a storm of ooms.

A regression, I think.  A box-killing one on a pretty simple workload
on a not uncommon machine.

We used to handle this by scanning highmem even when there was plenty
of free highmem and the request is for a lowmmem pages.  We have made a
few changes in this area and I guess that's what broke it.


I think a suitable fix here would be to extend the
buffer_heads_over_limit special-case.  If buffer_heads_over_limit is
true, both direct-reclaimers and kswapd should scan the highmem zone
regardless of incoming gfp_mask and regardless of the highmem free
pages count.

In this mode, we only scan the file lru.  We should perform writeback
as well, because the buffer_heads might be dirty.

[aside: If all of a page's buffer_heads are dirty we can in fact
reclaim them and mark the entire page dirty.  If some of the
buffer_heads are dirty and the others are uptodate we can even reclaim
them in this case, and mark the entire page dirty, causing extra I/O
later.  But try_to_release_page() doesn't do these things.]


I think it is was always wrong that we only strip buffer_heads when
moving pages to the inactive list.  What happens if those 600MB of
buffer_heads are all attached to inactive pages?

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