Re: [PATCH] SUNRPC: use congestion_wait() in svc_alloc_args()

[Bruce Fields <bfields@fieldses.org>]

On Tue, Sep 07, 2021 at 02:53:48PM +0000, Chuck Lever III wrote:
> 
> 
> > On Sep 6, 2021, at 8:41 PM, NeilBrown <neilb@suse.de> 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.

Give up parallelism in return for at least hope of forward progress?
(Which should be possible as long as there's at least one server
thread.)

--b.