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

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Date:   Mon, 9 Oct 2017 08:24:26 +0200
From:   Michal Hocko <mhocko@...nel.org>
To:     Shakeel Butt <shakeelb@...gle.com>
Cc:     Alexander Viro <viro@...iv.linux.org.uk>,
        Vladimir Davydov <vdavydov.dev@...il.com>,
        Greg Thelen <gthelen@...gle.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

On Fri 06-10-17 12:33:03, Shakeel Butt wrote:
> >>       names_cachep = kmem_cache_create("names_cache", PATH_MAX, 0,
> >> -                     SLAB_HWCACHE_ALIGN|SLAB_PANIC, NULL);
> >> +                     SLAB_HWCACHE_ALIGN|SLAB_PANIC|SLAB_ACCOUNT, NULL);
> >
> > I might be wrong but isn't name cache only holding temporary objects
> > used for path resolution which are not stored anywhere?
> >
> 
> Even though they're temporary, many containers can together use a
> significant amount of transient uncharged memory. We've seen machines
> with 100s of MiBs in names_cache.

Yes that might be possible but are we prepared for random ENOMEM from
vfs calls which need to allocate a temporary name?

> 
> >>       filp_cachep = kmem_cache_create("filp", sizeof(struct file), 0,
> >> -                     SLAB_HWCACHE_ALIGN | SLAB_PANIC, NULL);
> >> +                     SLAB_HWCACHE_ALIGN | SLAB_PANIC | SLAB_ACCOUNT, NULL);
> >>       percpu_counter_init(&nr_files, 0, GFP_KERNEL);
> >>  }
> >
> > Don't we have a limit for the maximum number of open files?
> >
> 
> Yes, there is a system limit of maximum number of open files. However
> this limit is shared between different users on the system and one
> user can hog this resource. To cater that, we set the maximum limit
> very high and let the memory limit of each user limit the number of
> files they can open.

Similarly here. Are all syscalls allocating a fd prepared to return
ENOMEM?

-- 
Michal Hocko
SUSE Labs