linux-kernel - Re: [PATCH] fs, mm: account filp and names caches to kmemcg

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Date:   Fri, 13 Oct 2017 09:00:01 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Johannes Weiner <hannes@...xchg.org>
Cc:     Greg Thelen <gthelen@...gle.com>,
        Shakeel Butt <shakeelb@...gle.com>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linux MM <linux-mm@...ck.org>, linux-fsdevel@...r.kernel.org,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] fs, mm: account filp and names caches to kmemcg

Just to be explicit what I've had in mind. This hasn't been even compile
tested but it should provide at least an idea where I am trying to go..
---
diff --git a/mm/memcontrol.c b/mm/memcontrol.c
index d5f3a62887cf..91fa05372114 100644
--- a/mm/memcontrol.c
+++ b/mm/memcontrol.c
@@ -1528,26 +1528,36 @@ static void memcg_oom_recover(struct mem_cgroup *memcg)
 
 static void mem_cgroup_oom(struct mem_cgroup *memcg, gfp_t mask, int order)
 {
-	if (!current->memcg_may_oom)
-		return;
 	/*
 	 * We are in the middle of the charge context here, so we
 	 * don't want to block when potentially sitting on a callstack
 	 * that holds all kinds of filesystem and mm locks.
 	 *
-	 * Also, the caller may handle a failed allocation gracefully
-	 * (like optional page cache readahead) and so an OOM killer
-	 * invocation might not even be necessary.
+	 * cgroup v1 allowes sync users space handling so we cannot afford
+	 * to get stuck here for that configuration. That's why we don't do
+	 * anything here except remember the OOM context and then deal with
+	 * it at the end of the page fault when the stack is unwound, the 
+	 * locks are released, and when we know whether the fault was overall
+	 * successful.
 	 *
-	 * That's why we don't do anything here except remember the
-	 * OOM context and then deal with it at the end of the page
-	 * fault when the stack is unwound, the locks are released,
-	 * and when we know whether the fault was overall successful.
+	 * On the other hand, in-kernel OOM killer allows for an async victim
+	 * memory reclaim (oom_reaper) and that means that we are not solely
+	 * relying on the oom victim to make a forward progress so we can stay
+	 * in the the try_charge context and keep retrying as long as there
+	 * are oom victims to select.
 	 */
-	css_get(&memcg->css);
-	current->memcg_in_oom = memcg;
-	current->memcg_oom_gfp_mask = mask;
-	current->memcg_oom_order = order;
+	if (memcg->oom_kill_disable) {
+		if (!current->memcg_may_oom)
+			return false;
+		css_get(&memcg->css);
+		current->memcg_in_oom = memcg;
+		current->memcg_oom_gfp_mask = mask;
+		current->memcg_oom_order = order;
+
+		return false;
+	}
+
+	return mem_cgroup_out_of_memory(memcg, mask, order);
 }
 
 /**
@@ -2007,8 +2017,11 @@ static int try_charge(struct mem_cgroup *memcg, gfp_t gfp_mask,
 
 	mem_cgroup_event(mem_over_limit, MEMCG_OOM);
 
-	mem_cgroup_oom(mem_over_limit, gfp_mask,
-		       get_order(nr_pages * PAGE_SIZE));
+	if (mem_cgroup_oom(mem_over_limit, gfp_mask,
+		       get_order(nr_pages * PAGE_SIZE))) {
+		nr_retries = MEM_CGROUP_RECLAIM_RETRIES;
+		goto retry;
+	}
 nomem:
 	if (!(gfp_mask & __GFP_NOFAIL))
 		return -ENOMEM;
-- 
Michal Hocko
SUSE Labs