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From: John Hubbard <jhubbard@nvidia.com>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>,
	Christoph Hellwig <hch@infradead.org>,
	Ilya Dryomov <idryomov@gmail.com>, Jens Axboe <axboe@kernel.dk>,
	Jeff Layton <jlayton@kernel.org>, <linux-xfs@vger.kernel.org>,
	<linux-fsdevel@vger.kernel.org>, <linux-block@vger.kernel.org>,
	<ceph-devel@vger.kernel.org>, <linux-mm@kvack.org>,
	LKML <linux-kernel@vger.kernel.org>,
	John Hubbard <jhubbard@nvidia.com>
Subject: [PATCH 2/5] mm/gup: introduce pin_user_page()
Date: Fri, 21 Aug 2020 21:20:56 -0700	[thread overview]
Message-ID: <20200822042059.1805541-3-jhubbard@nvidia.com> (raw)
In-Reply-To: <20200822042059.1805541-1-jhubbard@nvidia.com>

pin_user_page() is the FOLL_PIN equivalent of get_page().

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 <jhubbard@nvidia.com>
---
 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 1983e08f5906..bee26614f430 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1149,6 +1149,8 @@ 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
  *
-- 
2.28.0


  parent reply	other threads:[~2020-08-22  4:21 UTC|newest]

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-08-22  4:20 [PATCH 0/5] bio: Direct IO: convert to pin_user_pages_fast() John Hubbard
2020-08-22  4:20 ` [PATCH 1/5] iov_iter: introduce iov_iter_pin_user_pages*() routines John Hubbard
2020-08-22  4:20 ` John Hubbard [this message]
2020-08-22  4:20 ` [PATCH 3/5] bio: convert get_user_pages_fast() --> pin_user_pages_fast() John Hubbard
2020-08-22  4:20 ` [PATCH 4/5] bio: introduce BIO_FOLL_PIN flag John Hubbard
2020-08-23  6:25   ` Christoph Hellwig
2020-08-23  6:57     ` John Hubbard
2020-08-24  7:36       ` John Hubbard
2020-08-24  9:20     ` Jens Axboe
2020-08-24 14:42       ` Christoph Hellwig
2020-08-22  4:20 ` [PATCH 5/5] fs/ceph: use pipe_get_pages_alloc() for pipe John Hubbard
2020-08-24 10:53   ` Jeff Layton
2020-08-24 17:54     ` John Hubbard
2020-08-24 18:47       ` Jeff Layton
2020-08-24 18:54         ` Matthew Wilcox
2020-08-24 19:02           ` John Hubbard
2020-08-25  1:20           ` [PATCH v2] " John Hubbard
2020-08-25 16:22             ` Jeff Layton
2020-08-25  1:54 ` [PATCH 0/5] bio: Direct IO: convert to pin_user_pages_fast() Al Viro
2020-08-25  2:07   ` Al Viro
2020-08-25  2:13     ` John Hubbard
2020-08-25  2:07   ` John Hubbard
2020-08-25  2:22     ` Al Viro
2020-08-25  2:27       ` John Hubbard

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