linux-kernel - [PATCH 4/4] mm: clarify mm_struct.mm

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Message-Id: <20161218123229.22952-4-vegard.nossum@oracle.com>
Date:   Sun, 18 Dec 2016 13:32:29 +0100
From:   Vegard Nossum <vegard.nossum@...cle.com>
To:     Andrew Morton <akpm@...ux-foundation.org>,
        Michal Hocko <mhocko@...e.com>, linux-mm@...ck.org
Cc:     Peter Zijlstra <peterz@...radead.org>,
        "Kirill A . Shutemov" <kirill@...temov.name>,
        linux-kernel@...r.kernel.org,
        Vegard Nossum <vegard.nossum@...cle.com>
Subject: [PATCH 4/4] mm: clarify mm_struct.mm_{users,count} documentation

Clarify documentation relating to mm_users and mm_count, and switch to
kernel-doc syntax.

Signed-off-by: Vegard Nossum <vegard.nossum@...cle.com>
---
 include/linux/mm_types.h | 23 +++++++++++++++++++++--
 1 file changed, 21 insertions(+), 2 deletions(-)

diff --git a/include/linux/mm_types.h b/include/linux/mm_types.h
index 08d947fc4c59..316c3e1fc226 100644
--- a/include/linux/mm_types.h
+++ b/include/linux/mm_types.h
@@ -407,8 +407,27 @@ struct mm_struct {
 	unsigned long task_size;		/* size of task vm space */
 	unsigned long highest_vm_end;		/* highest vma end address */
 	pgd_t * pgd;
-	atomic_t mm_users;			/* How many users with user space? */
-	atomic_t mm_count;			/* How many references to "struct mm_struct" (users count as 1) */
+
+	/**
+	 * @mm_users: The number of users including userspace.
+	 *
+	 * Use mmget()/mmget_not_zero()/mmput() to modify. When this drops
+	 * to 0 (i.e. when the task exits and there are no other temporary
+	 * reference holders), we also release a reference on @mm_count
+	 * (which may then free the &struct mm_struct if @mm_count also
+	 * drops to 0).
+	 */
+	atomic_t mm_users;
+
+	/**
+	 * @mm_count: The number of references to &struct mm_struct
+	 * (@mm_users count as 1).
+	 *
+	 * Use mmgrab()/mmdrop() to modify. When this drops to 0, the
+	 * &struct mm_struct is freed.
+	 */
+	atomic_t mm_count;
+
 	atomic_long_t nr_ptes;			/* PTE page table pages */
 #if CONFIG_PGTABLE_LEVELS > 2
 	atomic_long_t nr_pmds;			/* PMD page table pages */
-- 
2.11.0.1.gaa10c3f