On Tue, Jul 21, 2015 at 04:34:12PM -0700, Andrew Morton wrote:

On Sun, 19 Jul 2015 15:31:11 +0300 Vladimir Davydov [off-list ref] wrote:

quoted

Hwpoison allows to filter pages by memory cgroup ino. Currently, it
calls try_get_mem_cgroup_from_page to obtain the cgroup from a page and
then its ino using cgroup_ino, but now we have an apter method for that,
page_cgroup_ino, so use it instead.

I assume "an apter" was supposed to be "a helper"?

Yes, sounds better :-)

quoted

--- a/mm/hwpoison-inject.c
+++ b/mm/hwpoison-inject.c

@@ -45,12 +45,9 @@ static int hwpoison_inject(void *data, u64 val)
 	/*
 	 * do a racy check with elevated page count, to make sure PG_hwpoison
 	 * will only be set for the targeted owner (or on a free page).
-	 * We temporarily take page lock for try_get_mem_cgroup_from_page().
 	 * memory_failure() will redo the check reliably inside page lock.
 	 */
-	lock_page(hpage);
 	err = hwpoison_filter(hpage);
-	unlock_page(hpage);
 	if (err)
 		goto put_out;
 

@@ -126,7 +123,7 @@ static int pfn_inject_init(void)
 	if (!dentry)
 		goto fail;
 
-#ifdef CONFIG_MEMCG_SWAP
+#ifdef CONFIG_MEMCG
 	dentry = debugfs_create_u64("corrupt-filter-memcg", 0600,
 				    hwpoison_dir, &hwpoison_filter_memcg);
 	if (!dentry)

Confused.  We're changing the conditions under which this debugfs file
is created.  Is this a typo or some unchangelogged thing or what?

This is an unchangelogged cleanup. In fact, there had been a comment
regarding it before v6, but then it got lost. Sorry about that. The
commit message should look like this:

"""
Hwpoison allows to filter pages by memory cgroup ino. Currently, it
calls try_get_mem_cgroup_from_page to obtain the cgroup from a page and
then its ino using cgroup_ino, but now we have a helper method for that,
page_cgroup_ino, so use it instead.

This patch also loosens the hwpoison memcg filter dependency rules - it
makes it depend on CONFIG_MEMCG instead of CONFIG_MEMCG_SWAP, because
hwpoison memcg filter does not require anything (nor it used to) from
CONFIG_MEMCG_SWAP side.
"""

Or we can simply revert this cleanups if you don't like it:
---

diff --git a/mm/hwpoison-inject.c b/mm/hwpoison-inject.c
index 5015679014c1..1cd105ee5a7b 100644
--- a/mm/hwpoison-inject.c
+++ b/mm/hwpoison-inject.c

@@ -123,7 +123,7 @@ static int pfn_inject_init(void)
 	if (!dentry)
 		goto fail;
 
-#ifdef CONFIG_MEMCG
+#ifdef CONFIG_MEMCG_SWAP
 	dentry = debugfs_create_u64("corrupt-filter-memcg", 0600,
 				    hwpoison_dir, &hwpoison_filter_memcg);
 	if (!dentry)

diff --git a/mm/memory-failure.c b/mm/memory-failure.c
index 97005396a507..5ea7d8c760fa 100644
--- a/mm/memory-failure.c
+++ b/mm/memory-failure.c

@@ -130,7 +130,7 @@ static int hwpoison_filter_flags(struct page *p)
  * can only guarantee that the page either belongs to the memcg tasks, or is
  * a freed page.
  */
-#ifdef CONFIG_MEMCG
+#ifdef CONFIG_MEMCG_SWAP
 u64 hwpoison_filter_memcg;
 EXPORT_SYMBOL_GPL(hwpoison_filter_memcg);
 static int hwpoison_filter_task(struct page *p)