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Date:   Wed,  6 May 2020 17:41:45 -0700
From:   Anthony Yznaga <anthony.yznaga@...cle.com>
To:     linux-mm@...ck.org, linux-kernel@...r.kernel.org
Cc:     willy@...radead.org, corbet@....net, tglx@...utronix.de,
        mingo@...hat.com, bp@...en8.de, x86@...nel.org, hpa@...or.com,
        dave.hansen@...ux.intel.com, luto@...nel.org, peterz@...radead.org,
        rppt@...ux.ibm.com, akpm@...ux-foundation.org, hughd@...gle.com,
        ebiederm@...ssion.com, masahiroy@...nel.org, ardb@...nel.org,
        ndesaulniers@...gle.com, dima@...ovin.in, daniel.kiper@...cle.com,
        nivedita@...m.mit.edu, rafael.j.wysocki@...el.com,
        dan.j.williams@...el.com, zhenzhong.duan@...cle.com,
        jroedel@...e.de, bhe@...hat.com, guro@...com,
        Thomas.Lendacky@....com, andriy.shevchenko@...ux.intel.com,
        keescook@...omium.org, hannes@...xchg.org, minchan@...nel.org,
        mhocko@...nel.org, ying.huang@...el.com,
        yang.shi@...ux.alibaba.com, gustavo@...eddedor.com,
        ziqian.lzq@...fin.com, vdavydov.dev@...il.com,
        jason.zeng@...el.com, kevin.tian@...el.com, zhiyuan.lv@...el.com,
        lei.l.li@...el.com, paul.c.lai@...el.com, ashok.raj@...el.com,
        linux-fsdevel@...r.kernel.org, linux-doc@...r.kernel.org,
        kexec@...ts.infradead.org
Subject: [RFC 19/43] mm: PKRAM: allow preserved memory to be freed from userspace

To free all space utilized for preserved memory, one can write 0 to
/sys/kernel/pkram. This will destroy all PKRAM nodes that are not
currently being read or written.

Originally-by: Vladimir Davydov <vdavydov.dev@...il.com>
Signed-off-by: Anthony Yznaga <anthony.yznaga@...cle.com>
---
 mm/pkram.c | 39 ++++++++++++++++++++++++++++++++++++++-
 1 file changed, 38 insertions(+), 1 deletion(-)

diff --git a/mm/pkram.c b/mm/pkram.c
index 0aaaf9b79682..95e691382721 100644
--- a/mm/pkram.c
+++ b/mm/pkram.c
@@ -509,6 +509,32 @@ static void pkram_truncate_node(struct pkram_node *node)
 	node->obj_pfn = 0;
 }
 
+/*
+ * Free all nodes that are not under operation.
+ */
+static void pkram_truncate(void)
+{
+	struct page *page, *tmp;
+	struct pkram_node *node;
+	LIST_HEAD(dispose);
+
+	mutex_lock(&pkram_mutex);
+	list_for_each_entry_safe(page, tmp, &pkram_nodes, lru) {
+		node = page_address(page);
+		if (!(node->flags & PKRAM_ACCMODE_MASK))
+			list_move(&page->lru, &dispose);
+	}
+	mutex_unlock(&pkram_mutex);
+
+	while (!list_empty(&dispose)) {
+		page = list_first_entry(&dispose, struct page, lru);
+		list_del(&page->lru);
+		node = page_address(page);
+		pkram_truncate_node(node);
+		pkram_free_page(node);
+	}
+}
+
 static void pkram_add_link(struct pkram_link *link, struct pkram_obj *obj)
 {
 	link->link_pfn = obj->link_pfn;
@@ -1141,8 +1167,19 @@ static ssize_t show_pkram_sb_pfn(struct kobject *kobj,
 	return sprintf(buf, "%lx\n", pfn);
 }
 
+static ssize_t store_pkram_sb_pfn(struct kobject *kobj,
+		struct kobj_attribute *attr, const char *buf, size_t count)
+{
+	int val;
+
+	if (kstrtoint(buf, 0, &val) || val)
+		return -EINVAL;
+	pkram_truncate();
+	return count;
+}
+
 static struct kobj_attribute pkram_sb_pfn_attr =
-	__ATTR(pkram, 0444, show_pkram_sb_pfn, NULL);
+	__ATTR(pkram, 0644, show_pkram_sb_pfn, store_pkram_sb_pfn);
 
 static struct attribute *pkram_attrs[] = {
 	&pkram_sb_pfn_attr.attr,
-- 
2.13.3

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