linux-kernel - Re: [PATCHv2] mm: Account pud page tables

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Message-ID: <20170926094344.t4cws4v4vrie5de5@node.shutemov.name>
Date:   Tue, 26 Sep 2017 12:43:44 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Michal Hocko <mhocko@...nel.org>
Cc:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Vlastimil Babka <vbabka@...e.cz>
Subject: Re: [PATCHv2] mm: Account pud page tables

On Mon, Sep 25, 2017 at 03:53:05PM +0200, Michal Hocko wrote:
> On Mon 25-09-17 16:07:15, Kirill A. Shutemov wrote:
> > On Mon, Sep 25, 2017 at 01:54:30PM +0200, Michal Hocko wrote:
> > > On Mon 25-09-17 10:39:13, Kirill A. Shutemov wrote:
> > > > On machine with 5-level paging support a process can allocate
> > > > significant amount of memory and stay unnoticed by oom-killer and
> > > > memory cgroup. The trick is to allocate a lot of PUD page tables.
> > > > We don't account PUD page tables, only PMD and PTE.
> > > > 
> > > > We already addressed the same issue for PMD page tables, see
> > > > dc6c9a35b66b ("mm: account pmd page tables to the process").
> > > > Introduction 5-level paging bring the same issue for PUD page tables.
> > > > 
> > > > The patch expands accounting to PUD level.
> > > 
> > > OK, we definitely need this or something like that but I really do not
> > > like how much code we actually need for each pte level for accounting.
> > > Do we really need to distinguish each level? Do we have any arch that
> > > would use a different number of pages to back pte/pmd/pud?
> > 
> > Looks like we actually do. At least on mips. See PMD_ORDER/PUD_ORDER.
> 
> Hmm, but then oom_badness does consider them a single page which is
> wrong. I haven't checked other users. Anyway even if we've had different
> sizes why cannot we deal with this in callers. They know which level of
> page table they allocate/free, no?

So do you want to see single counter for all page table levels?
Do we have anybody who relies on VmPTE/VmPMD now?

-- 
 Kirill A. Shutemov