[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <ZDnVETTFus3BFLxH@x1n>
Date: Fri, 14 Apr 2023 18:34:57 -0400
From: Peter Xu <peterx@...hat.com>
To: Suren Baghdasaryan <surenb@...gle.com>
Cc: akpm@...ux-foundation.org, willy@...radead.org, hannes@...xchg.org,
mhocko@...e.com, josef@...icpanda.com, jack@...e.cz,
ldufour@...ux.ibm.com, laurent.dufour@...ibm.com,
michel@...pinasse.org, liam.howlett@...cle.com, jglisse@...gle.com,
vbabka@...e.cz, minchan@...gle.com, dave@...olabs.net,
punit.agrawal@...edance.com, lstoakes@...il.com,
linux-mm@...ck.org, linux-kernel@...r.kernel.org,
kernel-team@...roid.com
Subject: Re: [PATCH 1/1] mm: do not increment pgfault stats when page fault
handler retries
Hi, Suren,
On Fri, Apr 14, 2023 at 03:14:23PM -0700, Suren Baghdasaryan wrote:
> > It also already ignores invalid faults:
> >
> > if (ret & (VM_FAULT_ERROR | VM_FAULT_RETRY))
> > return;
>
> Can there be a case of (!VM_FAULT_ERROR && VM_FAULT_RETRY) - basically
> we need to retry but no errors happened? If so then this condition
> would double-count pagefaults in such cases.
If ret==VM_FAULT_RETRY it should return here already, so I assume
mm_account_fault() itself is fine regarding fault retries?
Note that I think "ret & (VM_FAULT_ERROR | VM_FAULT_RETRY)" above means
"either ERROR or RETRY we'll skip the accounting".
IMHO we should have 3 cases here:
- ERROR && !RETRY
error triggered of any kind
- RETRY && !ERROR
we need to try one more time
- !RETRY && !ERROR
we finished the fault
I don't think ERROR & RETRY can even be set at the same time so I assume
there's no option 4) - a RETRY should imply no ERROR already, even though
it's still incomplete so need another attempt.
Thanks,
--
Peter Xu
Powered by blists - more mailing lists