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

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Date:   Fri, 2 Nov 2018 00:58:23 +0000
From:   Roman Gushchin <guro@...com>
To:     Dexuan Cui <decui@...rosoft.com>
CC:     "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>,
        Michal Hocko <mhocko@...nel.org>,
        "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, 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@...r.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!