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From: "Lance Yang" Message-ID: <63cc131c78e6fe37755b3e39f90558469a0e80f4@linux.dev> TLS-Required: No Subject: Re: [RESEND PATCH v2 1/1] mm/rmap: add CONFIG_MM_ID guard for folio_test_large_maybe_mapped_shared() To: "David Hildenbrand" , "Andrew Morton" Cc: mingzhe.yang@ly.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org, "Lance Yang" In-Reply-To: References: <20250418152228.20545-1-lance.yang@linux.dev> <20250420162925.2c58c018defee9ee192be553@linux-foundation.org> <641755b75b4ecb9c9822e15e707a0ebf1e250788@linux.dev> <1c81b176893c349dfb12feaebd17e0694fedec0b@linux.dev> X-Migadu-Flow: FLOW_OUT X-Rspam-User: X-Rspamd-Queue-Id: 8316CA000B X-Rspamd-Server: rspam04 X-Stat-Signature: cxcc3kuzd6qnoh57nejggiyfxku7dah4 X-HE-Tag: 1745221833-663456 X-HE-Meta: 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 pB1JiOaN j3apRrlHS9zR0wUfGLMxZLgO1R+eHhQeSl5GDx71XzXpuBOjiaUoLuBq7USnu0N0JdM484B/o0Mp825LEOglql6C33K9oFeabKmipmx8kbBRB0r7CycjMBrsJek1twoWcO1j0uMtgPcwUWb5E+697HGaEQjbhQh7KuoTyZlovbXuvYbzPcIAIJUsDm+CGY1+Mk16z8f3G7ltFA6IS9pfh0Av7K/3BeEvOG3qQH/dWR8qYuusmB/lqoDpd9TjAb8DgEpMlGzEB9a21eZ96cY4VihFtCWbcrXN35m8n/xj9Q+QVDXk09vAQhoz7Y8Ikwfh5qta5n1ZZcZA7Hkk= 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: April 21, 2025 at 3:17 PM, "David Hildenbrand" wrote: >=20 >=20On 21.04.25 07:16, Lance Yang wrote: >=20 >=20>=20 >=20> April 21, 2025 at 1:13 PM, "Lance Yang" wrot= e: > >=20 >=20> > >> > >=20 >=20> >=20 >=20> > April 21, 2025 at 7:29 AM, "Andrew Morton" wrote: > > >=20 >=20>=20 >=20> On Fri, 18 Apr 2025 23:22:28 +0800 Lance Yang wrote: > >=20 >=20> >>> > >=20 >=20> >>> > >=20 >=20> From: Lance Yang > >=20 >=20> >>> > >=20 >=20> >>> > >=20 >=20> >>> > >=20 >=20> To prevent folio_test_large_maybe_mapped_shared() from being used = without > >=20 >=20> >>> > >=20 >=20> CONFIG_MM_ID, we add a compile-time check rather than wrapping it = in > >=20 >=20> >>> > >=20 >=20> '#ifdef', avoiding even more #ifdef in callers that already use > >=20 >=20> >>> > >=20 >=20> IS_ENABLED(CONFIG_MM_ID). > >=20 >=20> >>> > >=20 >=20> >>> > >=20 >=20> >>> > >=20 >=20> Also, we used plenty of IS_ENABLED() on purpose to keep the code f= ree of > >=20 >=20> >>> > >=20 >=20> '#ifdef' mess. > >=20 >=20> >>> > >=20 >=20> >>> > >=20 >=20> I dunno, this just seems really whacky. > >=20 >=20> >=20 >=20> > I'd hope David could leave some comments on that. > > >=20 >=20>=20 >=20> --- a/include/linux/page-flags.h > >=20 >=20> >>> > >=20 >=20> +++ b/include/linux/page-flags.h > >=20 >=20> >>> > >=20 >=20> @@ -1232,6 +1232,8 @@ static inline int folio_has_private(const st= ruct folio *folio) > >=20 >=20> >>> > >=20 >=20> >>> > >=20 >=20> >>> > >=20 >=20> static inline bool folio_test_large_maybe_mapped_shared(const stru= ct folio *folio) > >=20 >=20> >>> > >=20 >=20> { > >=20 >=20> >>> > >=20 >=20> + /* This function should never be called without CONFIG_MM_ID ena= bled. */ > >=20 >=20> >>> > >=20 >=20> >>> > >=20 >=20> A correcter comment would be "This function should never be compil= ed > >=20 >=20> >>> > >=20 >=20> without CONFIG_MM_ID enabled". > >=20 >=20> >=20 >=20> > Yes, that is more exact ;) > > >=20 >=20>=20 >=20> Which lets the cat out of the bag. Why the heck is it being compil= ed > >=20 >=20> >>> > >=20 >=20> with CONFIG_MM_ID=3Dn?? We have tools to prevent that. > >=20 >=20> >>> > >=20 >=20> Can we just slap "#ifdef CONFIG_MM_ID" around the whole function? = It > >=20 >=20> >>> > >=20 >=20> should have no callers, right? If the linker ends up complaining t= hen > >=20 >=20> >>> > >=20 >=20> something went wrong. > >=20 >=20> >=20 >=20> > The reason we can't simply add #ifdef CONFIG_MM_ID around folio_t= est_large_maybe_mapped_shared() > > >=20 >=20> > is because its caller folio_maybe_mapped_shared() relies on IS_E= NABLED(CONFIG_MM_ID). > > >=20 >=20>=20 >=20> static inline bool folio_maybe_mapped_shared(struct folio *folio) > >=20 >=20> { > >=20 >=20> [...] > >=20 >=20> if (!IS_ENABLED(CONFIG_MM_ID)) > >=20 >=20> return true; > >=20 >=20> [...] > >=20 >=20> return folio_test_large_maybe_mapped_shared(folio); > >=20 >=20> } > >=20 >=20> folio_maybe_mapped_shared() is always available - doesn't depend o= n > >=20 >=20> CONFIG_MM_ID or CONFIG_TRANSPARENT_HUGEPAGE. > >=20 >=20 > We could #ifdef in folio_maybe_mapped_shared(), which I find rather sub= optimal ... >=20 >=20or simply inline it into the 4 callers. >=20 >=20That might be the best approach, given that only selected user should= be using the low-level primitive and everybody else should be using foli= o_maybe_mapped_shared(). Yep, I tend to prefer the second approach as well, given there are only four callers. Andrew, wdyt? Thanks, Lance >=20 >=20-- Cheers, >=20 >=20David / dhildenb >