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

From: Roman Gushchin <guro@fb.com>
To: Dexuan Cui <decui@microsoft.com>
Cc: "linux-mm@kvack.org" <linux-mm@kvack.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Kernel Team <Kernel-team@fb.com>,
	"Shakeel Butt" <shakeelb@google.com>,
	Michal Hocko <mhocko@kernel.org>,
	"Johannes Weiner" <hannes@cmpxchg.org>, Tejun Heo <tj@kernel.org>,
	Rik van Riel <riel@surriel.com>,
	Konstantin Khlebnikov <koct9i@gmail.com>,
	Matthew Wilcox <willy@infradead.org>,
	"Stable@vger.kernel.org" <Stable@vger.kernel.org>
Subject: Re: Will the recent memory leak fixes be backported to longterm kernels?
Date: Fri, 2 Nov 2018 00:58:23 +0000	[thread overview]
Message-ID: <20181102005816.GA10297@tower.DHCP.thefacebook.com> (raw)
In-Reply-To: <PU1P153MB0169CB6382E0F047579D111DBFCF0@PU1P153MB0169.APCP153.PROD.OUTLOOK.COM>

On Fri, Nov 02, 2018 at 12:16:02AM +0000, Dexuan Cui wrote:
> Hi all,
> When debugging a memory leak issue (https://github.com/coreos/bugs/issues/2516)
> with v4.14.11-coreos, we noticed the same issue may have been fixed recently by
> Roman in the latest mainline (i.e. Linus's master branch) according to comment #7 of 
> https://urldefense.proofpoint.com/v2/url?u=https-3A__bugs.launchpad.net_ubuntu_-2Bsource_linux_-2Bbug_1792349&d=DwIFAg&c=5VD0RTtNlTh3ycd41b3MUw&r=i6WobKxbeG3slzHSIOxTVtYIJw7qjCE6S0spDTKL-J4&m=mrT9jcrhFvVxDpVBlxihJg6S6U91rlevOJby7y1YynE&s=1eHLVA-oQGqMd2ujRPU8kZMbkShOuIDD5CUgpM1IzGI&e=, which lists these
> patches (I'm not sure if the 5-patch list is complete):
> 
> 010cb21d4ede math64: prevent double calculation of DIV64_U64_ROUND_UP() arguments
> f77d7a05670d mm: don't miss the last page because of round-off error
> d18bf0af683e mm: drain memcg stocks on css offlining
> 71cd51b2e1ca mm: rework memcg kernel stack accounting
> f3a2fccbce15 mm: slowly shrink slabs with a relatively small number of objects
> 
> Obviously at least some of the fixes are also needed in the longterm kernels like v4.14.y,
> but none of the 5 patches has the "Cc: stable@vger.kernel.org" tag? I'm wondering if
> these patches will be backported to the longterm kernels. BTW, the patches are not
> in v4.19, but I suppose they will be in v4.19.1-rc1?

Hello, Dexuan!

A couple of issues has been revealed recently, here are fixes
(hashes are from the next tree):

5f4b04528b5f mm: don't reclaim inodes with many attached pages
5a03b371ad6a mm: handle no memcg case in memcg_kmem_charge() properly

These two patches should be added to the serie.

Re stable backporting, I'd really wait for some time. Memory reclaim is a
quite complex and fragile area, so even if patches are correct by themselves,
they can easily cause a regression by revealing some other issues (as it was
with the inode reclaim case).

Thanks!