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Tue, 21 Nov 2023 08:46:11 -0800 (PST) Received: from unknowna0e70b2ca394.attlocal.net ([2600:1700:2f7d:1800::16]) by smtp.gmail.com with ESMTPSA id i133-20020a81548b000000b005a206896d62sm3143442ywb.111.2023.11.21.08.46.10 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 21 Nov 2023 08:46:11 -0800 (PST) Date: Tue, 21 Nov 2023 08:46:08 -0800 From: Vishal Moola To: Alexander Gordeev Cc: Heiko Carstens , Andrew Morton , linux-mm@kvack.org, linux-s390@vger.kernel.org, linux-kernel@vger.kernel.org, Gerald Schaefer Subject: Re: [PATCH v2] pgtable: do not expose _refcount field via ptdesc Message-ID: References: <20231121120310.696335-1-agordeev@linux.ibm.com> <20231121144717.6318-A-hca@linux.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Server: rspam08 X-Rspamd-Queue-Id: C22E42002B X-Stat-Signature: e616ipfb6g1i6epyofknygfjmkzoyg3h X-Rspam-User: X-HE-Tag: 1700585172-633751 X-HE-Meta: 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 0QOvK64K 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, Nov 21, 2023 at 04:45:21PM +0100, Alexander Gordeev wrote: > Since commit d08d4e7cd6bf ("s390/mm: use full 4KB page for 2KB PTE") > _refcount field is not used for fragmented page tracking on s390 and > there is no other code left that accesses this field explicitly. > > Suggested-by: Heiko Carstens > Signed-off-by: Alexander Gordeev > --- > include/linux/mm_types.h | 7 +++---- > 1 file changed, 3 insertions(+), 4 deletions(-) > > diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h > index 957ce38768b2..ce0cfc6e4d94 100644 > --- a/include/linux/mm_types.h > +++ b/include/linux/mm_types.h > @@ -401,11 +401,11 @@ FOLIO_MATCH(compound_head, _head_2a); > * @pmd_huge_pte: Protected by ptdesc->ptl, used for THPs. > * @__page_mapping: Aliases with page->mapping. Unused for page tables. > * @pt_mm: Used for x86 pgds. > - * @pt_frag_refcount: For fragmented page table tracking. Powerpc and s390 only. > + * @pt_frag_refcount: For fragmented page table tracking. Powerpc only. > * @_pt_pad_2: Padding to ensure proper alignment. > * @ptl: Lock for the page table. > * @__page_type: Same as page->page_type. Unused for page tables. > - * @_refcount: Same as page refcount. Used for s390 page tables. > + * @_pt_pad_3: Padding that aliases with page's refcount. I like updating the documentation, but I'd rather see _refcount renamed to __page_refcount similar to the other unused page fields. _pt_pad_* is used for variables that aren't present in struct page (and are required for padding). > * @pt_memcg_data: Memcg data. Tracked for page tables here. > * > * This struct overlays struct page for now. Do not modify without a good > @@ -438,7 +438,7 @@ struct ptdesc { > #endif > }; > unsigned int __page_type; > - atomic_t _refcount; > + unsigned int _pt_pad_3; > #ifdef CONFIG_MEMCG > unsigned long pt_memcg_data; > #endif > @@ -452,7 +452,6 @@ TABLE_MATCH(compound_head, _pt_pad_1); > TABLE_MATCH(mapping, __page_mapping); > TABLE_MATCH(rcu_head, pt_rcu_head); > TABLE_MATCH(page_type, __page_type); > -TABLE_MATCH(_refcount, _refcount); Its still a good idea to keep this check. In the case of !CONFIG_MEMCG, _refcount is the last variable of ptdesc and if some change were to happen that caused it to be misaligned we will want to know. > #ifdef CONFIG_MEMCG > TABLE_MATCH(memcg_data, pt_memcg_data); > #endif > -- > 2.39.2 > >