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Date: Sun, 1 Jul 2018 19:50:59 -0700
From: Matthew Wilcox <willy@infradead.org>
Subject: Re: [BUG] Swap xarray workingset eviction warning.
Message-ID: <20180702025059.GA9865@bombadil.infradead.org>
References: <2920a634-0646-1500-7c4d-62c56932fe49@gmail.com>
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To: Peter Geis <pgwipeout@gmail.com>
Cc: linux-fsdevel@vger.kernel.org, Johannes Weiner <hannes@cmpxchg.org>, linux-mm@kvack.org

On Sun, Jul 01, 2018 at 07:09:41PM -0400, Peter Geis wrote:
> The warning is as follows:
> [10409.408904] ------------[ cut here ]------------
> [10409.408912] WARNING: CPU: 0 PID: 38 at ./include/linux/xarray.h:53
> workingset_eviction+0x14c/0x154

This is interesting.  Here's the code that leads to the warning:

static void *pack_shadow(int memcgid, pg_data_t *pgdat, unsigned long eviction)
{
        eviction >>= bucket_order;
        eviction = (eviction << MEM_CGROUP_ID_SHIFT) | memcgid;
        eviction = (eviction << NODES_SHIFT) | pgdat->node_id;

        return xa_mk_value(eviction);
}

The warning itself comes from:

static inline void *xa_mk_value(unsigned long v)
{
        WARN_ON((long)v < 0);
        return (void *)((v << 1) | 1);
}

The fact that we haven't seen this on other architectures makes me wonder
if NODES_SHIFT or MEM_CGROUP_ID_SHIFT are messed up on Tegra?

Johannes, I wonder if you could help out here?  I'm not terribly familiar
with this part of the workingset code.