From: "Aneesh Kumar K.V" <aneesh.kumar@linux•vnet.ibm.com>
To: Benjamin Herrenschmidt <benh@kernel•crashing.org>,
paulus@samba•org, mpe@ellerman•id.au
Cc: linuxppc-dev@lists•ozlabs.org
Subject: Re: [PATCH 1/3] powerpc/mm/radix: Update pte update sequence for pte clear case
Date: Thu, 09 Feb 2017 10:04:51 +0530 [thread overview]
Message-ID: <87zihwouc4.fsf@skywalker.in.ibm.com> (raw)
In-Reply-To: <1486613729.3401.15.camel@kernel.crashing.org>
Benjamin Herrenschmidt <benh@kernel•crashing.org> writes:
> On Thu, 2017-02-09 at 14:49 +1100, Benjamin Herrenschmidt wrote:
>> On Thu, 2017-02-09 at 08:28 +0530, Aneesh Kumar K.V wrote:
>> > In the kernel we do follow the below sequence in different code
>> > paths.
>> > pte = ptep_get_clear(ptep)
>> > ....
>> > set_pte_at(ptep, pte)
>> >
>> > We do that for mremap, autonuma protection update and softdirty
>> > clearing. This
>> > implies our optimization to skip a tlb flush when clearing a pte
>> > update is
>> > not valid, because for DD1 system that followup set_pte_at will be
>> > done witout
>> > doing the required tlbflush. Fix that by always doing the dd1 style
>> > pte update
>> > irrespective of new_pte value. In a later patch we will optimize
>> > the application
>> > exit case.
>>
>> What about my change to set_pte_at() ? We seem to be overwriting
>> valid PTEs,
>> shouldn't we deal with that ?
>
> So the HW guys confirmed that the TLB will never cache a valid entry
> that has all permissions clear. That leaves the THP write problem
> though.
Which is fixed by the autonuma related changes posted at
https://lkml.kernel.org/r/1486609259-6796-1-git-send-email-aneesh.kumar@linux.vnet.ibm.com
Right now i am running a kernel compile in loop with parallel perf
bench numa mem run to make sure we got most of the details correct.
(this is on p8)
-aneesh
next prev parent reply other threads:[~2017-02-09 4:35 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-02-09 2:58 [PATCH 1/3] powerpc/mm/radix: Update pte update sequence for pte clear case Aneesh Kumar K.V
2017-02-09 2:58 ` [PATCH 2/3] powerpc/mm/radix: Use ptep_get_and_clear_full when clearing pte for full mm Aneesh Kumar K.V
2017-02-14 4:17 ` Michael Neuling
2017-02-09 2:58 ` [PATCH 3/3] powerpc/mm/radix: Skip ptesync in pte update helpers Aneesh Kumar K.V
2017-02-14 4:17 ` Michael Neuling
2017-02-09 3:49 ` [PATCH 1/3] powerpc/mm/radix: Update pte update sequence for pte clear case Benjamin Herrenschmidt
2017-02-09 4:15 ` Benjamin Herrenschmidt
2017-02-09 4:34 ` Aneesh Kumar K.V [this message]
2017-02-14 4:17 ` Michael Neuling
2017-02-16 5:59 ` [1/3] " Michael Ellerman
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