On Tue, Apr 26, 2011 at 08:53:30PM +1000, NeilBrown wrote:

On Tue, 26 Apr 2011 11:36:46 +0100 Mel Gorman [off-list ref] wrote:

quoted

On Tue, Apr 26, 2011 at 07:49:47PM +1000, NeilBrown wrote:

quoted

quoted

Maybe a
   WARN_ON((gfp_mask & __GFP_MEMALLOC) && (gfp_mask & __GFP_NOMEMALLOC));
might be wise?

Both MEMALLOC and NOMEMALLOC are related to PFMEMALLOC reserves so
it's reasonable for them to have similar names. This warning will
also trigger because it's a combination of flags that does happen.

Consider for example

any interrupt
  -> __netdev_alloc_skb		(mask == GFP_ATOMIC)
    -> __alloc_skb		(mask == GFP_ATOMIC)
       if (sk_memalloc_socks() && (flags & SKB_ALLOC_RX))
               gfp_mask |= __GFP_MEMALLOC;
				(mask == GFP_ATOMIC|__GFP_NOMEMALLOC)
      -> __kmalloc_reserve
		First attempt tries to avoid reserves so adds __GFP_MEMALLOC
				(mask == GFP_ATOMIC|__GFP_NOMEMALLOC|__GFP_MEMALLOC)

You have the "NO"s mixed up a bit which confused me for a while :-)
But I see your point - I guess the WARN_ON isn't really needed.

Bah, that was unhelpful on my part. I'm glad you saw the point anyway.
Sorry about that.

-- 
Mel Gorman
SUSE Labs

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