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b=dySeBa+/bT7WPrUOlSM+GoWCvzrThfqEJXPqBeuo0dWsgt0rn9h/R9bhCxF5FrYlS ViWqh6qDmJedlPmZ2QyiLDJvNlF6GEcmwLp4kuQYiQwlD4ukyP35Tu3bGtfJ20KkcY 6vRLNACAJKwqw+SBClHwSgxJw0zN+tIN5O1SoFOY= Date: Thu, 17 Apr 2025 15:02:37 -0700 From: Andrew Morton To: Lance Yang Cc: david@redhat.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Mingzhe Yang Subject: Re: [PATCH 1/1] mm/rmap: add CONFIG_MM_ID guard for folio_test_large_maybe_mapped_shared() Message-Id: <20250417150237.ba3bbb3f55f992c692932841@linux-foundation.org> In-Reply-To: <20250417124908.58543-1-ioworker0@gmail.com> References: <20250417124908.58543-1-ioworker0@gmail.com> X-Mailer: Sylpheed 3.7.0 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspamd-Queue-Id: 5C9361C000A X-Rspam-User: X-Rspamd-Server: rspam07 X-Stat-Signature: fs17gqzny4rswb6e7aw6ataa7toixbwd X-HE-Tag: 1744927359-972513 X-HE-Meta: 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 JTwy8L4c w3jSs 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 Thu, 17 Apr 2025 20:49:08 +0800 Lance Yang wrote: > Add a compile-time check to make sure folio_test_large_maybe_mapped_shared() > is only used with CONFIG_MM_ID enabled, as it directly accesses the _mm_ids > field that only works under CONFIG_MM_ID. > > ... > > --- a/include/linux/page-flags.h > +++ b/include/linux/page-flags.h > @@ -1232,6 +1232,8 @@ static inline int folio_has_private(const struct folio *folio) > > static inline bool folio_test_large_maybe_mapped_shared(const struct folio *folio) > { > + /* This function should never be called without CONFIG_MM_ID enabled. */ > + BUILD_BUG_ON(!IS_ENABLED(CONFIG_MM_ID)); > return test_bit(FOLIO_MM_IDS_SHARED_BITNUM, &folio->_mm_ids); > } > #undef PF_ANY I don't get it. Sounds like we're adding a compile-time check to check for a compilation error which would have happened anyway. If folio_test_large_maybe_mapped_shared() is only used with CONFIG_MM_ID enabled, then do #ifdef CONFIG_MM_ID static inline bool folio_test_large_maybe_mapped_shared(...) { } #endif ? Or, as "_mm_ids field only works under CONFIG_MM_ID", make it not-even-present when !CONFIG_MM_ID? --- a/include/linux/mm_types.h~a +++ a/include/linux/mm_types.h @@ -438,7 +438,9 @@ struct folio { mm_id_mapcount_t _mm_id_mapcount[2]; union { mm_id_t _mm_id[2]; +#ifdef CONFIG_MM_ID unsigned long _mm_ids; +#endif }; /* private: the union with struct page is transitional */ }; _ or --- a/include/linux/mm_types.h~a +++ a/include/linux/mm_types.h @@ -436,10 +436,12 @@ struct folio { atomic_t _pincount; #endif /* CONFIG_64BIT */ mm_id_mapcount_t _mm_id_mapcount[2]; +#ifdef CONFIG_MM_ID union { mm_id_t _mm_id[2]; unsigned long _mm_ids; }; +#endif /* private: the union with struct page is transitional */ }; unsigned long _usable_1[4]; _ I dunno, it sounds like something hasn't been fully thought through here. It's hard to say because the changelog is unclear. Perhaps start out by fully describing what problem the patch is addressing?