linux-kernel - Re: [RFC V2 12/12] mm: Tag VMA with VM_CDM flag explicitly during mbind(MPOL

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Tue, 7 Feb 2017 10:07:28 -0800
From:   Dave Hansen <dave.hansen@...el.com>
To:     Anshuman Khandual <khandual@...ux.vnet.ibm.com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Cc:     mhocko@...e.com, vbabka@...e.cz, mgorman@...e.de,
        minchan@...nel.org, aneesh.kumar@...ux.vnet.ibm.com,
        bsingharora@...il.com, srikar@...ux.vnet.ibm.com,
        haren@...ux.vnet.ibm.com, jglisse@...hat.com,
        dan.j.williams@...el.com
Subject: Re: [RFC V2 12/12] mm: Tag VMA with VM_CDM flag explicitly during
 mbind(MPOL_BIND)

On 01/30/2017 08:36 PM, Anshuman Khandual wrote:
> On 01/30/2017 11:24 PM, Dave Hansen wrote:
>> On 01/29/2017 07:35 PM, Anshuman Khandual wrote:
>>> +		if ((new_pol->mode == MPOL_BIND)
>>> +			&& nodemask_has_cdm(new_pol->v.nodes))
>>> +			set_vm_cdm(vma);
>> So, if you did:
>>
>> 	mbind(addr, PAGE_SIZE, MPOL_BIND, all_nodes, ...);
>> 	mbind(addr, PAGE_SIZE, MPOL_BIND, one_non_cdm_node, ...);
>>
>> You end up with a VMA that can never have KSM done on it, etc...  Even
>> though there's no good reason for it.  I guess /proc/$pid/smaps might be
>> able to help us figure out what was going on here, but that still seems
>> like an awful lot of damage.
> 
> Agreed, this VMA should not remain tagged after the second call. It does
> not make sense. For this kind of scenarios we can re-evaluate the VMA
> tag every time the nodemask change is attempted. But if we are looking for
> some runtime re-evaluation then we need to steal some cycles are during
> general VMA processing opportunity points like merging and split to do
> the necessary re-evaluation. Should do we do these kind two kinds of
> re-evaluation to be more optimal ?

I'm still unconvinced that you *need* detection like this.  Scanning big
VMAs is going to be really painful.

I thought I asked before but I can't find it in this thread.  But, we
have explicit interfaces for disabling KSM and khugepaged.  Why do we
need implicit ones like this in addition to those?