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Date:   Mon, 30 May 2022 14:29:31 -0400
From:   Peter Xu <peterx@redhat.com>
To:     Heiko Carstens <hca@linux.ibm.com>
Cc:     Christian Borntraeger <borntraeger@linux.ibm.com>,
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Subject: Re: [PATCH v4] mm: Avoid unnecessary page fault retires on shared
 memory types
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References: <20220527193936.30678-1-peterx@redhat.com>
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On Mon, May 30, 2022 at 07:03:31PM +0200, Heiko Carstens wrote:
> On Mon, May 30, 2022 at 12:00:52PM -0400, Peter Xu wrote:
> > On Mon, May 30, 2022 at 11:52:54AM -0400, Peter Xu wrote:
> > > On Mon, May 30, 2022 at 11:35:10AM +0200, Christian Borntraeger wrote:
> > > > > diff --git a/arch/s390/mm/fault.c b/arch/s390/mm/fault.c
> > > > > index 4608cc962ecf..e1d40ca341b7 100644
> > > > > --- a/arch/s390/mm/fault.c
> > > > > +++ b/arch/s390/mm/fault.c
> > > > > @@ -436,12 +436,11 @@ static inline vm_fault_t do_exception(struct pt_regs *regs, int access)
> > > > >   	/* The fault is fully completed (including releasing mmap lock) */
> > > > >   	if (fault & VM_FAULT_COMPLETED) {
> > > > > -		/*
> > > > > -		 * Gmap will need the mmap lock again, so retake it.  TODO:
> > > > > -		 * only conditionally take the lock when CONFIG_PGSTE set.
> > > > > -		 */
> > > > > -		mmap_read_lock(mm);
> > > > > -		goto out_gmap;
> > > > > +		if (gmap) {
> > > > > +			mmap_read_lock(mm);
> > > > > +			goto out_gmap;
> > > > > +		}
> 			fault = 0;  <----
> > > > > +		goto out;
> > 
> > Hmm, right after I replied I found "goto out" could be problematic, since
> > all s390 callers of do_exception() will assume it an error condition (side
> > note: "goto out_gmap" contains one step to clear "fault" to 0).  I'll
> > replace this with "return 0" instead if it looks good to both of you.
> > 
> > I'll wait for a confirmation before reposting.  Thanks,
> 
> Right, that was stupid. Thanks for double checking!
> 
> However could you please add "fault = 0" just in front of the goto out
> like above? I'd like to avoid having returns and gotos mixed.

Sure thing.

-- 
Peter Xu