Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1575932

Re: [RFC V2 12/12] mm: Tag VMA with VM_CDM flag explicitly during mbind(MPOL_BIND)

Show all headers | View raw

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?

Back to linux.kernel | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

Re: [RFC V2 12/12] mm: Tag VMA with VM_CDM flag explicitly during  mbind(MPOL_BIND) Anshuman Khandual <khandual@linux.vnet.ibm.com> - 2017-01-31 05:40 +0100
  Re: [RFC V2 12/12] mm: Tag VMA with VM_CDM flag explicitly during  mbind(MPOL_BIND) Dave Hansen <dave.hansen@intel.com> - 2017-02-07 19:10 +0100
    Re: [RFC V2 12/12] mm: Tag VMA with VM_CDM flag explicitly during  mbind(MPOL_BIND) Anshuman Khandual <khandual@linux.vnet.ibm.com> - 2017-02-08 17:50 +0100
    Re: [RFC V2 12/12] mm: Tag VMA with VM_CDM flag explicitly during  mbind(MPOL_BIND) Jerome Glisse <jglisse@redhat.com> - 2017-02-08 19:40 +0100

csiph-web