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Date:   Thu, 18 Mar 2021 16:46:25 -0700
From:   Andrew Morton <akpm@linux-foundation.org>
To:     Jens Axboe <axboe@kernel.dk>
Cc:     Shakeel Butt <shakeelb@google.com>,
        Dan Schatzberg <schatzberg.dan@gmail.com>,
        Tejun Heo <tj@kernel.org>, Zefan Li <lizefan.x@bytedance.com>,
        Johannes Weiner <hannes@cmpxchg.org>,
        Michal Hocko <mhocko@kernel.org>,
        Vladimir Davydov <vdavydov.dev@gmail.com>,
        Hugh Dickins <hughd@google.com>, Roman Gushchin <guro@fb.com>,
        Muchun Song <songmuchun@bytedance.com>,
        Alex Shi <alex.shi@linux.alibaba.com>,
        Alexander Duyck <alexander.h.duyck@linux.intel.com>,
        Chris Down <chris@chrisdown.name>,
        Yafang Shao <laoar.shao@gmail.com>,
        Wei Yang <richard.weiyang@gmail.com>,
        "open list:BLOCK LAYER" <linux-block@vger.kernel.org>,
        open list <linux-kernel@vger.kernel.org>,
        "open list:CONTROL GROUP (CGROUP)" <cgroups@vger.kernel.org>,
        "open list:MEMORY MANAGEMENT" <linux-mm@kvack.org>
Subject: Re: [PATCH v10 0/3] Charge loop device i/o to issuing cgroup
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On Thu, 18 Mar 2021 10:00:17 -0600 Jens Axboe <axboe@kernel.dk> wrote:

> On 3/18/21 9:53 AM, Shakeel Butt wrote:
> > On Wed, Mar 17, 2021 at 3:30 PM Jens Axboe <axboe@kernel.dk> wrote:
> >>
> >> On 3/16/21 9:36 AM, Dan Schatzberg wrote:
> >>> No major changes, just rebasing and resubmitting
> >>
> >> Applied for 5.13, thanks.
> >>
> > 
> > I have requested a couple of changes in the patch series. Can this
> > applied series still be changed or new patches are required?
> 
> I have nothing sitting on top of it for now, so as far as I'm concerned
> we can apply a new series instead. Then we can also fold in that fix
> from Colin that he posted this morning...

The collision in memcontrol.c is a pain, but I guess as this is mainly
a loop patch, the block tree is an appropriate route.

Here's the collision between "mm: Charge active memcg when no mm is
set" and Shakeels's
https://lkml.kernel.org/r/20210305212639.775498-1-shakeelb@google.com


--- mm/memcontrol.c
+++ mm/memcontrol.c
@@ -6728,8 +6730,15 @@ int mem_cgroup_charge(struct page *page, struct mm_struct *mm, gfp_t gfp_mask)
 		rcu_read_unlock();
 	}
 
-	if (!memcg)
-		memcg = get_mem_cgroup_from_mm(mm);
+	if (!memcg) {
+		if (!mm) {
+			memcg = get_mem_cgroup_from_current();
+			if (!memcg)
+				memcg = get_mem_cgroup_from_mm(current->mm);
+		} else {
+			memcg = get_mem_cgroup_from_mm(mm);
+		}
+	}
 
 	ret = try_charge(memcg, gfp_mask, nr_pages);
 	if (ret)


Which I resolved thusly:

int mem_cgroup_charge(struct page *page, struct mm_struct *mm, gfp_t gfp_mask)
{
	struct mem_cgroup *memcg;
	int ret;

	if (mem_cgroup_disabled())
		return 0;

	if (!mm) {
		memcg = get_mem_cgroup_from_current();
		(!memcg)
			memcg = get_mem_cgroup_from_mm(current->mm);
	} else {
		memcg = get_mem_cgroup_from_mm(mm);
	}
				
	ret = __mem_cgroup_charge(page, memcg, gfp_mask);
	css_put(&memcg->css);

	return ret;
}