linux-kernel - Re: [PATCH v16 08/11] secretmem: add memcg accounting

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Date:   Mon, 25 Jan 2021 23:35:26 +0200
From:   Mike Rapoport <rppt@...nel.org>
To:     Shakeel Butt <shakeelb@...gle.com>
Cc:     Matthew Wilcox <willy@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Andy Lutomirski <luto@...nel.org>,
        Arnd Bergmann <arnd@...db.de>, Borislav Petkov <bp@...en8.de>,
        Catalin Marinas <catalin.marinas@....com>,
        Christopher Lameter <cl@...ux.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        David Hildenbrand <david@...hat.com>,
        Elena Reshetova <elena.reshetova@...el.com>,
        "H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...hat.com>,
        James Bottomley <jejb@...ux.ibm.com>,
        "Kirill A. Shutemov" <kirill@...temov.name>,
        Mark Rutland <mark.rutland@....com>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Michael Kerrisk <mtk.manpages@...il.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Rick Edgecombe <rick.p.edgecombe@...el.com>,
        Roman Gushchin <guro@...com>, Shuah Khan <shuah@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Tycho Andersen <tycho@...ho.ws>, Will Deacon <will@...nel.org>,
        linux-api@...r.kernel.org, linux-arch@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Linux MM <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-kselftest@...r.kernel.org, linux-nvdimm@...ts.01.org,
        linux-riscv@...ts.infradead.org, x86@...nel.org,
        Hagen Paul Pfeifer <hagen@...u.net>,
        Palmer Dabbelt <palmerdabbelt@...gle.com>
Subject: Re: [PATCH v16 08/11] secretmem: add memcg accounting

On Mon, Jan 25, 2021 at 09:18:04AM -0800, Shakeel Butt wrote:
> On Mon, Jan 25, 2021 at 8:20 AM Matthew Wilcox <willy@...radead.org> wrote:
> >
> > On Thu, Jan 21, 2021 at 02:27:20PM +0200, Mike Rapoport wrote:
> > > From: Mike Rapoport <rppt@...ux.ibm.com>
> > >
> > > Account memory consumed by secretmem to memcg. The accounting is updated
> > > when the memory is actually allocated and freed.

I though about doing per-page accounting, but then one would be able to
create a lot of secretmem file descriptors, use only a page from each while
actual memory consumption will be way higher.

> > I think this is wrong.  It fails to account subsequent allocators from
> > the same PMD.  If you want to track like this, you need separate pools
> > per memcg.
> >
> 
> Are these secretmem pools shared between different jobs/memcgs?

A secretmem pool is per anonymous file descriptor and this file descriptor
can be shared only explicitly between several processes. So, the secretmem
pool should not be shared between different jobs/memcg. Of course, it's
possible to spread threads of a process across different memcgs, but in
that case the accounting will be similar to what's happening today with
sl*b. The first thread to cause kmalloc() will be charged for the
allocation of the entire slab and subsequent allocations from that slab
will not be accounted.

That said, having a pool per memcg will add ton of complexity with very
dubious value.

-- 
Sincerely yours,
Mike.