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Sat, 29 Aug 2020 01:08:55 -0700 X-PGP-Universal: processed; by hqpgpgate101.nvidia.com on Sat, 29 Aug 2020 01:08:55 -0700 Received: from HQMAIL107.nvidia.com (172.20.187.13) by HQMAIL107.nvidia.com (172.20.187.13) with Microsoft SMTP Server (TLS) id 15.0.1473.3; Sat, 29 Aug 2020 08:08:54 +0000 Received: from hqnvemgw03.nvidia.com (10.124.88.68) by HQMAIL107.nvidia.com (172.20.187.13) with Microsoft SMTP Server (TLS) id 15.0.1473.3 via Frontend Transport; Sat, 29 Aug 2020 08:08:54 +0000 Received: from sandstorm.nvidia.com (Not Verified[10.2.50.252]) by hqnvemgw03.nvidia.com with Trustwave SEG (v7,5,8,10121) id ; Sat, 29 Aug 2020 01:08:54 -0700 From: John Hubbard To: Andrew Morton CC: Alexander Viro , Christoph Hellwig , Ilya Dryomov , Jens Axboe , , , , , LKML , John Hubbard Subject: [PATCH v2 1/3] mm/gup: introduce pin_user_page() Date: Sat, 29 Aug 2020 01:08:51 -0700 Message-ID: <20200829080853.20337-2-jhubbard@nvidia.com> X-Mailer: git-send-email 2.28.0 In-Reply-To: <20200829080853.20337-1-jhubbard@nvidia.com> References: <20200829080853.20337-1-jhubbard@nvidia.com> MIME-Version: 1.0 X-NVConfidentiality: public DKIM-Signature: v=1; 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This was always a missing piece of the pin/unpin API calls (early reviewers of pin_user_pages() asked about it, in fact), but until now, it just wasn't needed. Finally though, now that the Direct IO pieces in block/bio are about to be converted to use FOLL_PIN, it turns out that there are some cases in which get_page() and get_user_pages_fast() were both used. Converting those sites requires a drop-in replacement for get_page(), which this patch supplies. [1] and [2] provide some background about pin_user_pages() in general. [1] "Explicit pinning of user-space pages": https://lwn.net/Articles/807108/ [2] Documentation/core-api/pin_user_pages.rst Signed-off-by: John Hubbard --- include/linux/mm.h | 2 ++ mm/gup.c | 30 ++++++++++++++++++++++++++++++ 2 files changed, 32 insertions(+) diff --git a/include/linux/mm.h b/include/linux/mm.h index 97c83773b6f0..51c6ae4b63f7 100644 --- a/include/linux/mm.h +++ b/include/linux/mm.h @@ -1152,6 +1152,8 @@ static inline void get_page(struct page *page) page_ref_inc(page); } +void pin_user_page(struct page *page); + bool __must_check try_grab_page(struct page *page, unsigned int flags); static inline __must_check bool try_get_page(struct page *page) diff --git a/mm/gup.c b/mm/gup.c index ae096ea7583f..2cae5bbbc862 100644 --- a/mm/gup.c +++ b/mm/gup.c @@ -123,6 +123,36 @@ static __maybe_unused struct page *try_grab_compound_head(struct page *page, return NULL; } +/* + * pin_user_page() - elevate the page refcount, and mark as FOLL_PIN + * + * This the FOLL_PIN equivalent of get_page(). It is intended for use when the + * page will be released via unpin_user_page(). + */ +void pin_user_page(struct page *page) +{ + int refs = 1; + + page = compound_head(page); + + VM_BUG_ON_PAGE(page_ref_count(page) <= 0, page); + + if (hpage_pincount_available(page)) + hpage_pincount_add(page, 1); + else + refs = GUP_PIN_COUNTING_BIAS; + + /* + * Similar to try_grab_compound_head(): even if using the + * hpage_pincount_add/_sub() routines, be sure to + * *also* increment the normal page refcount field at least + * once, so that the page really is pinned. + */ + page_ref_add(page, refs); + + mod_node_page_state(page_pgdat(page), NR_FOLL_PIN_ACQUIRED, 1); +} + /** * try_grab_page() - elevate a page's refcount by a flag-dependent amount *