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Howlett" , Jens Axboe Cc: linux-kernel@vger.kernel.org, willy@infradead.org, linux-mm@kvack.org, Ritesh Harjani , linux-block@vger.kernel.org, linux-fsdevel@vger.kernel.org, "Darrick J . Wong" , mcgrof@kernel.org, gost.dev@samsung.com, kernel@pankajraghav.com, hch@lst.de, Pankaj Raghav Subject: [PATCH v2 4/5] mm: add largest_zero_folio() routine Date: Fri, 8 Aug 2025 14:11:40 +0200 Message-ID: <20250808121141.624469-5-kernel@pankajraghav.com> In-Reply-To: <20250808121141.624469-1-kernel@pankajraghav.com> References: <20250808121141.624469-1-kernel@pankajraghav.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: 42AF9140002 X-Stat-Signature: qog7co4tz57xjp798rtczs1i8zdhq8ko X-Rspam-User: X-Rspamd-Server: rspam08 X-HE-Tag: 1754655151-336912 X-HE-Meta: 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 tZLaeUJm KrYOV545C9FdTp7EOUqytj3Y3SIkMS5yEdNxG1XOoh+fg3BXukA3/Kuxj1/28Te+HYXHvBJTJKCmG/XEUT1afUYt0fDmvHW1wDKCYoGvUVdK2H7DtuHBfUoIK8f5PuRfI41Q1QiYdnm+ORogDStZhFAlrDJ8+z7B0d7J9Z05Qlx9rXrF7hPbel//U+fNNHEMvgnhG1L6Xg3tpX6f1FsBBOfcdqx2Z0fmgyiJR2BALMGUl+2wusWNTG179TUiObD1Y52ItHzHOzxpqX5wJp3nxAc8F0chj461jXz427AvxRqv7TzdJHMjlWXSHS8j+Ghl8bzCe3CFrIy/49hZTogThdIyIGjKpUutW1nG4rADbsOo9CXUdXP2NX34i1dgwR6c4KAFSwObFV77+vIkwEVkpFe6dYNBcvECMRsxFWICohhIaKOQ2LxkLnmLO0xbLMemAIja/DWPOgnjXxsnQUG2lA99ZWA== 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: From: Pankaj Raghav The callers of mm_get_huge_zero_folio() have access to a mm struct and the lifetime of the huge_zero_folio is tied to the lifetime of the mm struct. largest_zero_folio() will give access to huge_zero_folio when PERSISTENT_HUGE_ZERO_FOLIO config option is enabled for callers that do not want to tie the lifetime to a mm struct. This is very useful for filesystem and block layers where the request completions can be async and there is no guarantee on the mm struct lifetime. This function will return a ZERO_PAGE folio if PERSISTENT_HUGE_ZERO_FOLIO is disabled or if we failed to allocate a huge_zero_folio during early init. Co-developed-by: David Hildenbrand Signed-off-by: David Hildenbrand Signed-off-by: Pankaj Raghav --- include/linux/huge_mm.h | 22 ++++++++++++++++++++++ 1 file changed, 22 insertions(+) diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h index bd547857c6c1..14d424830fa8 100644 --- a/include/linux/huge_mm.h +++ b/include/linux/huge_mm.h @@ -714,4 +714,26 @@ static inline int split_folio_to_order(struct folio *folio, int new_order) return split_folio_to_list_to_order(folio, NULL, new_order); } +/** + * largest_zero_folio - Get the largest zero size folio available + * + * This function shall be used when mm_get_huge_zero_folio() cannot be + * used as there is no appropriate mm lifetime to tie the huge zero folio + * from the caller. + * + * Deduce the size of the folio with folio_size instead of assuming the + * folio size. + * + * Return: pointer to PMD sized zero folio if CONFIG_PERSISTENT_HUGE_ZERO_FOLIO + * is enabled or a single page sized zero folio + */ +static inline struct folio *largest_zero_folio(void) +{ + struct folio *folio = get_persistent_huge_zero_folio(); + + if (folio) + return folio; + + return page_folio(ZERO_PAGE(0)); +} #endif /* _LINUX_HUGE_MM_H */ -- 2.49.0