Hello, Alan. On Wed, Jul 27, 2016 at 04:45:19PM -0400, Alan Stern wrote: > > Hmm... That doesn't really make them dependable during memory reclaim. > > True. But it does mean that they can't cause a deadlock by waiting > indefinitely for some other memory to be paged out to the very device > they are on the access pathway for. > > > What happens when those allocations fail? > > The same thing that happens when any allocation fails -- the original > I/O request fails with -ENOMEM or the equivalent. In the case of > usb-storage, this is likely to trigger error recovery, which will need > to allocate memory of its own... A bad situation to get into. All that would do is deferring the deadlock, right? I'm not sure it makes a lot of sense to protect an IO path against memory pressure half-way. It either can be depended during memory reclaim or it can't. The use of GFP_NOIO / ATOMIC is probably increases the chance of IO errors under moderate memory pressure too when there are dependable memory backing devices (and there better be) which can push things forward if called upon. Can MM people please chime in? The question is about USB stoage devices and memory reclaim. USB doesn't guarantee forward progress under memory pressure but tries a best-effort attempt with GFP_NOIO and ATOMIC. Is this the right thing to do? Thanks. -- tejun -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
