linux-kernel - Re: [PATCH v8 0/2] Directed kmem charging

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Date:   Fri, 17 Aug 2018 09:04:25 -0400
From:   Johannes Weiner <hannes@...xchg.org>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Shakeel Butt <shakeelb@...gle.com>,
        Michal Hocko <mhocko@...nel.org>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Jan Kara <jack@...e.com>, Greg Thelen <gthelen@...gle.com>,
        Amir Goldstein <amir73il@...il.com>,
        Roman Gushchin <guro@...com>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        linux-kernel@...r.kernel.org, cgroups@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH v8 0/2] Directed kmem charging

On Wed, Aug 15, 2018 at 03:25:11PM -0700, Andrew Morton wrote:
> On Wed, 27 Jun 2018 12:12:48 -0700 Shakeel Butt <shakeelb@...gle.com> wrote:
> 
> > The Linux kernel's memory cgroup allows limiting the memory usage of
> > the jobs running on the system to provide isolation between the jobs.
> > All the kernel memory allocated in the context of the job and marked
> > with __GFP_ACCOUNT will also be included in the memory usage and be
> > limited by the job's limit.
> > 
> > The kernel memory can only be charged to the memcg of the process in
> > whose context kernel memory was allocated. However there are cases where
> > the allocated kernel memory should be charged to the memcg different
> > from the current processes's memcg. This patch series contains two such
> > concrete use-cases i.e. fsnotify and buffer_head.
> > 
> > The fsnotify event objects can consume a lot of system memory for large
> > or unlimited queues if there is either no or slow listener. The events
> > are allocated in the context of the event producer. However they should
> > be charged to the event consumer. Similarly the buffer_head objects can
> > be allocated in a memcg different from the memcg of the page for which
> > buffer_head objects are being allocated.
> > 
> > To solve this issue, this patch series introduces mechanism to charge
> > kernel memory to a given memcg. In case of fsnotify events, the memcg of
> > the consumer can be used for charging and for buffer_head, the memcg of
> > the page can be charged. For directed charging, the caller can use the
> > scope API memalloc_[un]use_memcg() to specify the memcg to charge for
> > all the __GFP_ACCOUNT allocations within the scope.
> 
> This patchset is not showing signs of having been well reviewed at
> this time.  Could people please take another look?

I don't have the mailing list archives for this anymore, but the
series as it stands in mmots looks good to me and incorporates all the
feedback I remember giving.

[ My only gripe really is that it applies current->active_memcg only
  to kmem charges, not others as well. Right now it doesn't matter,
  but I can see this costing a kernel developer implementing remote
  charges for something other than kmem some time to realize. ]

Anyway, please feel free to add

Acked-by: Johannes Weiner <hannes@...xchg.org>

for 1/2 and 2/2 plus their two fixlets.