Re: [PATCH 01/12] netvm: Prevent a stream-specific deadlock

On Tue, May 15, 2012 at 11:47:14AM +0200, Peter Zijlstra wrote:

On Tue, 2012-05-15 at 10:14 +0100, Mel Gorman wrote:

quoted

@@ -289,6 +289,18 @@ void sk_clear_memalloc(struct sock *sk)
        sock_reset_flag(sk, SOCK_MEMALLOC);
        sk->sk_allocation &= ~__GFP_MEMALLOC;
        static_key_slow_dec(&memalloc_socks);
+
+       /*
+        * SOCK_MEMALLOC is allowed to ignore rmem limits to ensure forward
+        * progress of swapping. However, if SOCK_MEMALLOC is cleared while
+        * it has rmem allocations there is a risk that the user of the
+        * socket cannot make forward progress due to exceeding the rmem
+        * limits. By rights, sk_clear_memalloc() should only be called
+        * on sockets being torn down but warn and reset the accounting if
+        * that assumption breaks.
+        */
+       if (WARN_ON(sk->sk_forward_alloc))

WARN_ON_ONCE() perhaps?

I do not expect SOCK_MEMALLOC to be cleared frequently at all with the
possible exception of swapon/swapoff stress tests. If the flag is being
cleared regularly with rmem tokens then that is interesting in itself
but a WARN_ON_ONCE would miss it.

quoted

+               sk_mem_reclaim(sk);
 } 

-- 
Mel Gorman
SUSE Labs
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