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smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=FIS3zgbw; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id BC6EF606A321; Wed, 11 Nov 2026 07:44:04 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=FIS3zgbw Received: by smtp.kernel.org (Postfix) with ESMTPSA id BC0311F00A06; Wed, 11 Nov 2026 07:44:01 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1794383044; bh=Z9RWwu7ZrdbjA/+NxwvyjbBT9j/m8TzxPE3PcvKEAL8=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=FIS3zgbwrSyy0PKttgXR+kQJschgcbgwzK3PbLmjMG9H8zSaGctP/fvk43C6fFom6 i1LDLytYQIwfO2numnAedMu3hQxhleqtydsLVrDs5b0+jSFAcPn75n9YTxy2BIvXEC mhuVFfzzqc5L4uXTtu9q9ybdqkR+4OeS5JMAmGdJ+brJmc756UdZyYhDhTKGrw6zBw nubQLpn0zrlU12xsPNmddER70eW7j+XNiOfxz3BTt8Sw2fu5zW9nfJnPRw0mr0TMea MrLnadxeUwsQ6T5Q3nzapZtRQiuJpAD0AWKSun0wdTkePVx9nRq0cEk4vfql+LBtzH J2V1nfhYgnfiQ== Message-ID: <3a1a3bb5-0b01-4f20-aa0e-74a952544b8c@kernel.org> Date: Wed, 11 Nov 2026 08:43:58 +0100 X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v3 2/3] mm: gup: allow long-term pins of CMA-allocated HugeTLB folios To: Qi Zheng , muchun.song@linux.dev, osalvador@suse.de, akpm@linux-foundation.org, azpijr@gmail.com, lance.yang@linux.dev, Qi Zheng Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, stable@vger.kernel.org References: <586d6c53ab7e4c64d6e89ad3cf0cf7e07dabbfaf.1794046188.git.zhengqi.arch@bytedance.com> <7abb3aa1-385a-422f-86bd-7aac9661c4d8@kernel.org> <423c9b28-ecf2-4fab-817d-2fb326690c73@linux.dev> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 11/9/26 04:10, Qi Zheng wrote: > > > On 11/8/26 1:58 AM, David Hildenbrand (Arm) wrote: >> On 11/7/26 11:30, Qi Zheng wrote: >>> From: Qi Zheng >>> >>> Long-term pinning treats explicitly CMA-allocated HugeTLB folios as >>> unpinnable, causing unnecessary migration or pinning failures. >>> >>> These folios already own their CMA bitmap ranges, and memory blocks >>> overlapping CMA areas cannot be offlined. Allow HugeTLB folios with >>> HPG_cma to be pinned directly, including in ZONE_MOVABLE. >>> >>> Fixes: cf11e85fc08c ("mm: hugetlb: optionally allocate gigantic hugepages using cma") >>> Cc: stable@vger.kernel.org >>> Suggested-by: Muchun Song >>> Signed-off-by: Qi Zheng >>> Acked-by: Muchun Song >>> Reviewed-by: Oscar Salvador >>> Reviewed-by: Jose A. Perez de Azpillaga >>> --- >>> include/linux/mm.h | 29 +---------------------------- >>> mm/gup.c | 31 +++++++++++++++++++++++++++++++ >>> 2 files changed, 32 insertions(+), 28 deletions(-) >>> >>> diff --git a/include/linux/mm.h b/include/linux/mm.h >>> index 2d0b8a4c9974f..75dd40265d3f4 100644 >>> --- a/include/linux/mm.h >>> +++ b/include/linux/mm.h >>> @@ -2975,35 +2975,8 @@ static inline bool is_zero_folio(const struct folio *folio) >>> return is_zero_page(&folio->page); >>> } >>> >>> -/* MIGRATE_CMA and ZONE_MOVABLE do not allow pin folios */ >>> #ifdef CONFIG_MIGRATION >>> -static inline bool folio_is_longterm_pinnable(struct folio *folio) >>> -{ >>> -#ifdef CONFIG_CMA >>> - int mt = folio_migratetype(folio); >>> - >>> - if (mt == MIGRATE_CMA || mt == MIGRATE_ISOLATE) >>> - return false; >>> -#endif >>> - /* The zero page can be "pinned" but gets special handling. */ >>> - if (is_zero_folio(folio)) >>> - return true; >>> - >>> - /* Coherent device memory must always allow eviction. */ >>> - if (folio_is_device_coherent(folio)) >>> - return false; >>> - >>> - /* >>> - * Filesystems can only tolerate transient delays to truncate and >>> - * hole-punch operations >>> - */ >>> - if (folio_is_fsdax(folio)) >>> - return false; >>> - >>> - /* Otherwise, non-movable zone folios can be pinned. */ >>> - return !folio_is_zone_movable(folio); >>> - >>> -} >> >> Moving code while adding new stuff to it, please don't. >> >> Move code first, then modify it. >> >> I don't want to play "find the difference between two pictures" on a Saturday >> evening. > You resent your series way too fast. Now we have discussions in to threads, congratulations ;) > ;), got it. > > I moved the code to resolve a build dependency. > Why can't that be resolved differently? What is the dependency? >> >>> +bool folio_is_longterm_pinnable(struct folio *folio); >>> #else >>> static inline bool folio_is_longterm_pinnable(struct folio *folio) >>> { >>> diff --git a/mm/gup.c b/mm/gup.c >>> index 2b405cce2ca5c..f41701c603500 100644 >>> --- a/mm/gup.c >>> +++ b/mm/gup.c >>> @@ -2216,6 +2216,37 @@ struct page *get_dump_page(unsigned long addr, int *locked) >>> >>> #ifdef CONFIG_MIGRATION >>> >>> +bool folio_is_longterm_pinnable(struct folio *folio) >>> +{ >>> +#ifdef CONFIG_CMA >>> + int mt = folio_migratetype(folio); >>> + >>> + /* These HugeTLB folios own the CMA memory, so they can be long-term pinned. */ >>> + if (folio_test_hugetlb(folio) && folio_test_hugetlb_cma(folio)) >>> + return true; >> More hugetlb hackery ... don't like that, sorry. > > Agree. > >> >> I think this just goes down to a problem we discussed a while ago that is >> independent of hugetlb: we'd need some way to identify that the the page was >> actually allocated by the CMA owner, and it's not just some other movable >> allcoation that ended up there. >> >> For something generic non-hugetlb thing, can't we call into CMA to ask whether >> the current chunk is marked allocated? > > The existing bitmap is set before allocation completes, so the range > may still contain borrowed movable pages. A set bit alone cannot > establish ownership. > > A generic query may need separate ownership tracking, such as an > owned_bitmap recording successfully allocated pages. Its updates and > lookups would also need to handle concurrency with fast GUP. Or simply two bitmaps? "trying allocation - allocated" -- Cheers, David