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Fri, 15 May 2026 06:15:02 -0700 (PDT) Date: Fri, 15 May 2026 13:15:01 +0000 In-Reply-To: <4074a816-9e75-45a6-8141-25459bcc106b@kernel.org> Mime-Version: 1.0 References: <20260513-page_alloc-unmapped-prep-v1-0-dacdf5402be8@google.com> <20260513-page_alloc-unmapped-prep-v1-4-dacdf5402be8@google.com> <4074a816-9e75-45a6-8141-25459bcc106b@kernel.org> X-Mailer: aerc 0.21.0 Message-ID: Subject: Re: [PATCH 4/4] mm/page_alloc: remove ifdefs from pindex helpers From: Brendan Jackman To: "Vlastimil Babka (SUSE)" , Brendan Jackman , Andrew Morton , Kairui Song , Qi Zheng , Shakeel Butt , Barry Song , Axel Rasmussen , Yuanchu Xie , Wei Xu , David Hildenbrand , Lorenzo Stoakes , "Liam R. Howlett" , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , "Rafael J. Wysocki" , Pavel Machek , Len Brown , Johannes Weiner , Zi Yan Cc: , , Content-Type: text/plain; charset="UTF-8" X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: 4282A14000A X-Rspam-User: X-Stat-Signature: uff7ac8cnjzqstkegx6a191aqtuq1xj4 X-HE-Tag: 1778850904-743605 X-HE-Meta: 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 QhhNBs2/ 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed May 13, 2026 at 5:19 PM UTC, Vlastimil Babka (SUSE) wrote: > On 5/13/26 14:35, Brendan Jackman wrote: >> The ifdefs are not technically needed here, everything used here is >> always defined. >> >> Switching to IS_ENABLED() makes the code a bit less tiresome to read. >> >> Reviewed-by: Vlastimil Babka (SUSE) >> Signed-off-by: Brendan Jackman >> --- >> mm/page_alloc.c | 30 ++++++++++++++---------------- >> 1 file changed, 14 insertions(+), 16 deletions(-) >> >> diff --git a/mm/page_alloc.c b/mm/page_alloc.c >> index 5d6144c8860ed10fd641184f389c4953465d5178..2985ad0ab1044bdfda8ccc7aaed2ded19b5ac7ed 100644 >> --- a/mm/page_alloc.c >> +++ b/mm/page_alloc.c >> @@ -650,19 +650,17 @@ static void bad_page(struct page *page, const char *reason) >> >> static inline unsigned int order_to_pindex(int migratetype, int order) >> { >> + if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE)) { >> + bool movable = migratetype == MIGRATE_MOVABLE; >> >> -#ifdef CONFIG_TRANSPARENT_HUGEPAGE >> - bool movable; >> - if (order > PAGE_ALLOC_COSTLY_ORDER) { >> - VM_BUG_ON(!is_pmd_order(order)); >> + if (order > PAGE_ALLOC_COSTLY_ORDER) { >> + VM_BUG_ON(!is_pmd_order(order)); >> >> - movable = migratetype == MIGRATE_MOVABLE; >> - >> - return NR_LOWORDER_PCP_LISTS + movable; >> + return NR_LOWORDER_PCP_LISTS + movable; >> + } >> + } else { >> + VM_BUG_ON(order > PAGE_ALLOC_COSTLY_ORDER); >> } >> -#else >> - VM_BUG_ON(order > PAGE_ALLOC_COSTLY_ORDER); >> -#endif > > Uh yeah, VM_BUG_ONs are frowned upon now. But doing a VM_WARN_ON_ONCE here > makes little sense. There's no safe fallback if we end up here with a wrong > value. Isn't that grounds for upgrading them to a real BUG then? My experience has been (I broke this code lots of times lol, I REALLY struggle with this arithmetic stuff) if something goes wrong here the machine quickly gets irrevocably and undebuggably borked. Crashing is the best case scenario. > And it's all internal to page alloc so I'd just drop those checks > completely at this point. But, I won't die on the above hill, if people really hate BUG that much happy to go with the flow. In that case, I'd suggest we drop them as a separate patch.