xfs: ensure reclaim cursor is reset correctly at end of AG
On a 32 bit highmem PowerPC machine, the XFS inode cache was growing without bound and exhausting low memory causing the OOM killer to be triggered. After some effort, the problem was reproduced on a 32 bit x86 highmem machine. The problem is that the per-ag inode reclaim index cursor was not getting reset to the start of the AG if the radix tree tag lookup found no more reclaimable inodes. Hence every further reclaim attempt started at the same index beyond where any reclaimable inodes lay, and no further background reclaim ever occurred from the AG. Without background inode reclaim the VM driven cache shrinker simply cannot keep up with cache growth, and OOM is the result. While the change that exposed the problem was the conversion of the inode reclaim to use work queues for background reclaim, it was not the cause of the bug. The bug was introduced when the cursor code was added, just waiting for some weird configuration to strike.... Signed-off-by: Dave Chinner <dchinner@redhat.com> Tested-By: Christian Kujau <lists@nerdbynature.de> Reviewed-by: Christoph Hellwig <hch@lst.de> Reviewed-by: Alex Elder <aelder@sgi.com>
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@ -926,6 +926,7 @@ restart:
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XFS_LOOKUP_BATCH,
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XFS_ICI_RECLAIM_TAG);
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if (!nr_found) {
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done = 1;
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rcu_read_unlock();
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break;
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}
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