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(Postfix) with ESMTPS; Fri, 8 May 2026 08:34:35 +0000 (GMT) Date: Fri, 8 May 2026 10:34:34 +0200 From: Alexander Gordeev To: "David Hildenbrand (Arm)" Cc: Wei Yang , Andrew Morton , Lorenzo Stoakes , Anshuman Khandual , Oscar Salvador , linux-s390@vger.kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Gerald Schaefer , Heiko Carstens , Vasily Gorbik Subject: Re: [PATCH v2] mm/page_vma_mapped_walk: Use ptep_get_lockless() for lockless access Message-ID: References: <20260504130434.2285053-1-agordeev@linux.ibm.com> <20260507093433.q5xybwumryxclnqy@master> <43815634-29d3-4fa4-b967-0e251ff32f73-agordeev@linux.ibm.com> <20260508010040.o7bypjnfceeqloeq@master> <4da2d354-808d-463e-ac85-5b1f3fd51618-agordeev@linux.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-TM-AS-GCONF: 00 X-Proofpoint-Reinject: loops=2 maxloops=12 X-Proofpoint-ORIG-GUID: yvYtRSDiaxp9bcv13EZwXbYOjcFwU-1e X-Proofpoint-GUID: 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definitions=2026-05-07_02,2026-05-06_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 clxscore=1015 spamscore=0 lowpriorityscore=0 malwarescore=0 suspectscore=0 adultscore=0 priorityscore=1501 bulkscore=0 phishscore=0 impostorscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2604200000 definitions=main-2605080081 X-Rspam-User: X-Rspamd-Queue-Id: D7887A0007 X-Rspamd-Server: rspam06 X-Stat-Signature: ir9duahtqw55c9iuckqpzq5rzp8jj176 X-HE-Tag: 1778229287-901215 X-HE-Meta: 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 8BakM+S7 v37O5jSZvvxYfnrDQ5NTb0Ngv6tvX+l++Uyjpvhwbq1ubCOMs03aK8AbZv0k5DIj2GJ4sUsN47mttXQZ7kuWKN4142T7pai+i7YeIW84lp08oB2KLRBQts5uemQ/C7wuC1PKM9yMaaNNVJGdwbg/S5nqwWtk4XyBnu3VvKoW7r+8yyPk6s0GboPF0A+wMN/mRHeMEOT1/l0gnEDtyrTsUeztSPcnLlIh1TTkPihUtmKvi38uHmrM8b+5Gs/iNm3thHjPsCBCR8ZWhiCGAB/ri40Ch+jkAB6ubHuCj6K0wuSuWC+JMM9xLX47zuEGKgOTWOd+4S2pbpvtgUvnJnfZW9OsoFQ== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, May 08, 2026 at 10:17:16AM +0200, David Hildenbrand (Arm) wrote: > >> So the rule here is: > >> > >> * ptep_get_lockless() could be used for locked and not locked > >> * ptep_get() only used when locked > >> > >> Right? > > > > Yes, this is my assumption. > > I agree, ptep_get_lockless() simply makes sense to return something sensible if > there are concurrent modifications (which cannot happen when the PTL is held). > > That's why only 32bit with 64bit PTEs and arm64 even has to special-case it. > > > We should clarify in the patch description that in the do-while loop, we might > or might not hold the PTL, and that calling ptep_get_lockless() with the PTL > held is OK. > > I wonder if it's more efficient and clearer, to use the correct variant, though? > > > diff --git a/mm/page_vma_mapped.c b/mm/page_vma_mapped.c > index a4d52fdb3056..36d97661a4e5 100644 > --- a/mm/page_vma_mapped.c > +++ b/mm/page_vma_mapped.c > @@ -187,6 +187,7 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw) > p4d_t *p4d; > pud_t *pud; > pmd_t pmde; > + pte_t pteval; > > /* The only possible pmd mapping has been handled on last iteration */ > if (pvmw->pmd && !pvmw->pte) > @@ -310,7 +311,11 @@ bool page_vma_mapped_walk(struct page_vma_mapped_walk *pvmw) > goto restart; > } > pvmw->pte++; > - } while (pte_none(ptep_get(pvmw->pte))); > + if (!pvmw->ptl) > + pteval = ptep_get_lockless(pvmw->pte); > + else > + pteval = ptep_get(pvmw->pte); > + } while (pte_none(pteval)); Looks fine to me. I will try and add it to the next version. > if (!pvmw->ptl) { > spin_lock(ptl); > > > -- > Cheers, > > David Thanks!