linux-kernel - Re: Will the recent memory leak fixes be backported to longterm kernels?

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Date:   Fri, 2 Nov 2018 18:48:23 +0100
From:   Michal Hocko <mhocko@...nel.org>
To:     Roman Gushchin <guro@...com>
Cc:     Dexuan Cui <decui@...rosoft.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Kernel Team <Kernel-team@...com>,
        Shakeel Butt <shakeelb@...gle.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Tejun Heo <tj@...nel.org>, Rik van Riel <riel@...riel.com>,
        Konstantin Khlebnikov <koct9i@...il.com>,
        Matthew Wilcox <willy@...radead.org>,
        "Stable@...r.kernel.org" <Stable@...r.kernel.org>
Subject: Re: Will the recent memory leak fixes be backported to longterm
 kernels?

On Fri 02-11-18 17:25:58, Roman Gushchin wrote:
> On Fri, Nov 02, 2018 at 05:51:47PM +0100, Michal Hocko wrote:
> > On Fri 02-11-18 16:22:41, Roman Gushchin wrote:
[...]
> > > 2) We do forget to scan the last page in the LRU list. So if we ended up with
> > > 1-page long LRU, it can stay there basically forever.
> > 
> > Why 
> > 		/*
> > 		 * If the cgroup's already been deleted, make sure to
> > 		 * scrape out the remaining cache.
> > 		 */
> > 		if (!scan && !mem_cgroup_online(memcg))
> > 			scan = min(size, SWAP_CLUSTER_MAX);
> > 
> > in get_scan_count doesn't work for that case?
> 
> No, it doesn't. Let's look at the whole picture:
> 
> 		size = lruvec_lru_size(lruvec, lru, sc->reclaim_idx);
> 		scan = size >> sc->priority;
> 		/*
> 		 * If the cgroup's already been deleted, make sure to
> 		 * scrape out the remaining cache.
> 		 */
> 		if (!scan && !mem_cgroup_online(memcg))
> 			scan = min(size, SWAP_CLUSTER_MAX);
> 
> If size == 1, scan == 0 => scan = min(1, 32) == 1.
> And after proportional adjustment we'll have 0.

My friday brain hurst when looking at this but if it doesn't work as
advertized then it should be fixed. I do not see any of your patches to
touch this logic so how come it would work after them applied?
-- 
Michal Hocko
SUSE Labs