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(p200300d82f2849002c244e201f219fbd.dip0.t-ipconnect.de. [2003:d8:2f28:4900:2c24:4e20:1f21:9fbd]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-454d5032fcbsm203995455e9.6.2025.07.15.07.16.10 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 15 Jul 2025 07:16:11 -0700 (PDT) Message-ID: <0793154d-a6ca-43b7-a0c3-01532d9cccc8@redhat.com> Date: Tue, 15 Jul 2025 16:16:09 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 4/5] mm: add largest_zero_folio() routine To: "Pankaj Raghav (Samsung)" , Suren Baghdasaryan , Ryan Roberts , Baolin Wang , Borislav Petkov , Ingo Molnar , "H . Peter Anvin" , Vlastimil Babka , Zi Yan , Mike Rapoport , Dave Hansen , Michal Hocko , Lorenzo Stoakes , Andrew Morton , Thomas Gleixner , Nico Pache , Dev Jain , "Liam R . Howlett" , Jens Axboe Cc: linux-kernel@vger.kernel.org, willy@infradead.org, linux-mm@kvack.org, x86@kernel.org, linux-block@vger.kernel.org, linux-fsdevel@vger.kernel.org, "Darrick J . Wong" , mcgrof@kernel.org, gost.dev@samsung.com, hch@lst.de, Pankaj Raghav References: <20250707142319.319642-1-kernel@pankajraghav.com> <20250707142319.319642-5-kernel@pankajraghav.com> From: David Hildenbrand Content-Language: en-US Organization: Red Hat In-Reply-To: <20250707142319.319642-5-kernel@pankajraghav.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 07.07.25 16:23, Pankaj Raghav (Samsung) wrote: > From: Pankaj Raghav > > Add largest_zero_folio() routine so that huge_zero_folio can be > used without the need to pass any mm struct. This will return ZERO_PAGE > folio if CONFIG_STATIC_PMD_ZERO_PAGE is disabled or if we failed to > allocate a PMD page from memblock. > > This routine can also be called even if THP is disabled. > > Signed-off-by: Pankaj Raghav > --- > include/linux/mm.h | 28 ++++++++++++++++++++++++++-- > 1 file changed, 26 insertions(+), 2 deletions(-) > > diff --git a/include/linux/mm.h b/include/linux/mm.h > index 428fe6d36b3c..d5543cf7b8e9 100644 > --- a/include/linux/mm.h > +++ b/include/linux/mm.h > @@ -4018,17 +4018,41 @@ static inline bool vma_is_special_huge(const struct vm_area_struct *vma) > > #endif /* CONFIG_TRANSPARENT_HUGEPAGE || CONFIG_HUGETLBFS */ > > +extern struct folio *huge_zero_folio; > +extern unsigned long huge_zero_pfn; No need for "extern". > + > #ifdef CONFIG_STATIC_PMD_ZERO_PAGE > extern void __init static_pmd_zero_init(void); > + > +/* > + * largest_zero_folio - Get the largest zero size folio available > + * > + * This function will return a PMD sized zero folio if CONFIG_STATIC_PMD_ZERO_PAGE > + * is enabled. Otherwise, a ZERO_PAGE folio is returned. > + * > + * Deduce the size of the folio with folio_size instead of assuming the > + * folio size. > + */ > +static inline struct folio *largest_zero_folio(void) > +{ > + if(!huge_zero_folio) Nit: if (!huge_zero_folio), but see below I assume this check is only in place to handle whether static allocation failed, correct? > + return page_folio(ZERO_PAGE(0)); > + > + return READ_ONCE(huge_zero_folio); READ_ONCE should not be required if it cannot get freed. > +} > + > #else > static inline void __init static_pmd_zero_init(void) > { > return; > } > + > +static inline struct folio *largest_zero_folio(void) > +{ > + return page_folio(ZERO_PAGE(0)); > +} > #endif Could we do: static inline struct folio *largest_zero_folio(void) { if (IS_ENABLED(CONFIG_STATIC_PMD_ZERO_PAGE) && likely(huge_zero_folio)) return huge_zero_folio; return page_folio(ZERO_PAGE(0)); } -- Cheers, David / dhildenb