linux-kernel - Re: [PATCHv2 0/2] remap_file

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Date:	Mon, 12 May 2014 18:59:15 +0400
From:	Konstantin Khlebnikov <koct9i@...il.com>
To:	"Kirill A. Shutemov" <kirill@...temov.name>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Armin Rigo <arigo@...es.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	linux-mm <linux-mm@...ck.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCHv2 0/2] remap_file_pages() decommission

On Mon, May 12, 2014 at 4:43 PM, Kirill A. Shutemov
<kirill@...temov.name> wrote:
> On Fri, May 09, 2014 at 08:14:08AM -0700, Linus Torvalds wrote:
>> On Fri, May 9, 2014 at 7:05 AM, Kirill A. Shutemov
>> <kirill.shutemov@...ux.intel.com> wrote:
>> >
>> > Hm. I'm confused here. Do we have any limit forced per-user?
>>
>> Sure we do. See "struct user_struct". We limit max number of
>> processes, open files, signals etc.
>>
>> > I only see things like rlimits which are copied from parrent.
>> > Is it what you want?
>>
>> No, rlimits are per process (although in some cases what they limit
>> are counted per user despite the _limits_ of those resources then
>> being settable per thread).
>>
>> So I was just thinking that if we raise the per-mm default limits,
>> maybe we should add a global per-user limit to make it harder for a
>> user to use tons and toms of vma's.
>
> Here's the first attempt.
>
> I'm not completely happy about current_user(). It means we rely on that
> user of mm owner task is always equal to user of current. Not sure if it's
> always the case.
>
> Other option is to make MM_OWNER is always on and lookup proper user
> through task_cred_xxx(rcu_dereference(mm->owner), user).
>
> From 5ee6f6dd721ada8eb66c84a91003ac1e3eb2970a Mon Sep 17 00:00:00 2001
> From: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
> Date: Mon, 12 May 2014 15:13:12 +0300
> Subject: [PATCH] mm: add per-user limit on mapping count
>
> We're going to increase per-mm map_count. To avoid non-obvious memory
> abuse by creating a lot of VMA's, let's introduce per-user limit.
>
> The limit is implemented as sysctl. For now value of limit is pretty
> arbitrary -- 2^20.
>
> sizeof(vm_area_struct) with my kernel config (DEBUG_KERNEL=n) is 184
> bytes. It means with the limit user can use up to 184 MiB of RAM in
> VMAs.
>
> The limit is not applicable for root (INIT_USER).

I don't like this.

Maybe we could just account VMAs into OOM-badness points and let
OOM-killer do its job?

--- a/mm/oom_kill.c
+++ b/mm/oom_kill.c
@@ -170,7 +170,9 @@ unsigned long oom_badness(struct task_struct *p,
struct mem_cgroup *memcg,
         * task's rss, pagetable and swap space use.
         */
        points = get_mm_rss(p->mm) + atomic_long_read(&p->mm->nr_ptes) +
-                get_mm_counter(p->mm, MM_SWAPENTS);
+                get_mm_counter(p->mm, MM_SWAPENTS) +
+                (long)p->mm->map_count *
+                       sizeof(struct vm_area_struct) / PAGE_SIZE;
        task_unlock(p);

        /*
--
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