Re: [PATCH 1/4] sunrpc: keep a count of swapfiles associated with the rpc_clnt

[Mel Gorman]

On Sat, May 30, 2015 at 08:03:10AM -0400, Jeff Layton wrote:
> Jerome reported seeing a warning pop when working with a swapfile on
> NFS. The nfs_swap_activate can end up calling sk_set_memalloc while
> holding the rcu_read_lock and that function can sleep.
> 
> To fix that, we need to take a reference to the xprt while holding the
> rcu_read_lock, set the socket up for swapping and then drop that
> reference. But, xprt_put is not exported and having NFS deal with the
> underlying xprt is a bit of layering violation anyway.
> 
> Fix this by adding a set of activate/deactivate functions that take a
> rpc_clnt pointer instead of an rpc_xprt, and have nfs_swap_activate and
> nfs_swap_deactivate call those.
> 
> Also, add a per-rpc_clnt atomic counter to keep track of the number of
> active swapfiles associated with it. When the counter does a 0->1
> transition, we enable swapping on the xprt, when we do a 1->0 transition
> we disable swapping on it.
> 
> This also allows us to be a bit more selective with the RPC_TASK_SWAPPER
> flag. If non-swapper and swapper clnts are sharing a xprt, then we only
> need to flag the tasks from the swapper clnt with that flag.
> 
> Cc: Mel Gorman <mgorman@xxxxxxx>
> Reported-by: Jerome Marchand <jmarchan@xxxxxxxxxx>
> Signed-off-by: Jeff Layton <jeff.layton@xxxxxxxxxxxxxxx>

Acked-by: Mel Gorman <mgorman@xxxxxxx>

-- 
Mel Gorman
SUSE Labs
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