Messages in this thread | | | Date | Wed, 02 Apr 2008 11:37:57 -0700 | From | "Kok, Auke" <> | Subject | Re: GFP_ATOMIC page allocation failures. |
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Jeff Garzik wrote: > Andrew Morton wrote: >> After you've read Nick's comments (which I pray you have not), and after >> you've convinced us and yourself of their wrongness, you might like to >> consider adding a __GFP_NOWARN to netdev_alloc_skb(). > > Already done so. Adding __GFP_NOWARN to netdev_alloc_skb() is wrong > for several reasons. > > It doesn't change the underlying conditions. > It doesn't fix the desire to stamp other drivers in this manner. > > And most importantly, it is not even correct: the handling of the > allocation failure remains delegated to the netdev_alloc_skb() users, > which may or may not be properly handling allocation failures. > > Put simply, you don't know if the caller is stupid or smart. And there > are a _lot_ of callers, do you really want to flag all of them? > > Many modern net drivers are smart, and quite gracefully handle > allocation failure without skipping a beat. > > But some are really dumb, and leave big holes in their DMA rings when > allocations fail. > > The warnings are valid _sometimes_, but not for others. So adding > __GFP_NOWARN to netdev_alloc_skb() unconditionally makes no sense, > except as an admission that the "spew when there is memory pressure" > idea was silly. > > > > Turning to Nick's comment, > >> It's still actually nice to know how often it is happening even for >> these known good sites because too much can indicate a problem and >> that you could actually bring performance up by tuning some things. > > then create a counter or acculuation buffer somewhere. > > We don't need spew every time there is memory pressure of this magnitude. > > IMO there are much better ways than printk(), to inform tasks, and > humans, of allocation failures.
FYI e1000 and family already count various levels of alloc failures resulting from this:
alloc_rx_buff_failed - page alloc failure (might be harmless) rx_no_buffer_count - no buffer available for HW to use (harmless, hw will retry) rx_missed_errors - hw dropped a packet because of above failures
still I personally think the page alloc warnings are a good thing and we've had several issues resolve quickly because of them.
shutting them up completely moves the focus to our driver which ends up being a victim of suspicion, and we have to circle around hard to convince the user otherwise.
Auke
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