> On Sep 6, 2021, at 8:41 PM, NeilBrown <neilb@xxxxxxx> wrote: > > When does a single-page GFP_KERNEL allocation fail? Ever? > > I know that if I add __GFP_NOFAIL then it won't fail and that is > preferred to looping. > I know that if I add __GFP_RETRY_MAILFAIL (or others) then it might > fail. > But that is the semantics for a plain GFP_KERNEL ?? > > I recall a suggestion one that it would only fail if the process was > being killed by the oom killer. That seems reasonable and would suggest > that retrying is really bad. Is that true? > > For svc_alloc_args(), it might be better to fail and have the calling > server thread exit. This would need to be combined with dynamic > thread-count management so that when a request arrived, a new thread > might be started. I don't immediately see a benefit to killing server threads during periods of memory exhaustion, but sometimes I lack imagination. > So maybe we really don't want reclaim_progress_wait(), and all current > callers of congestion_wait() which are just waiting for allocation to > succeed should be either change to use __GFP_NOFAIL, or to handle > failure. I had completely forgotten about GFP_NOFAIL. That seems like the preferred answer, as it avoids an arbitrary time-based wait for a memory resource. (And maybe svc_rqst_alloc() should also get the NOFAIL treatment?). The question in my mind is how the new alloc_pages_bulk() will behave when passed NOFAIL. I would expect that NOFAIL would simply guarantee that at least one page is allocated on every call. -- Chuck Lever
