On copy_page_to_iter_iovec function issue.

Below is result of perf report:

opy_page_to_iter_iovec /proc/kcore
       │ Disassembly of section load0: ▒
       │ ▒
       │ ffffffff813ff690 <load0>: ▒
 75,00 │ mov 0x10(%rcx),%rax ▒
       │ cmp %rdx,%rax ▒
       │ cmovbe %rax,%rdx ▒
       │ test %rdx,%rdx ▒
       │ ↓ je 29a ◆
       │ push %rbp ▒
       │ mov %rsi,%r8 ▒
       │ mov %rsp,%rbp ▒
       │ push %r15 ▒
       │ push %r14 ▒
       │ push %r13 ▒
       │ push %r12 ▒
       │ mov %rdx,%r15 ▒
       │ push %rbx ▒
       │ mov %rcx,%rbx ▒
       │ sub $0x20,%rsp ▒
       │ mov 0x18(%rcx),%r13 ▒
       │ mov 0x8(%rcx),%r12 ▒
       │ mov 0x8(%r13),%r14 ▒
       │ mov %r12,%rax ▒
       │ add 0x0(%r13),%rax ▒
       │ sub %r12,%r14 ▒
       │ cmp %rdx,%r14 ▒
       │ mov %rax,%rsi ▒
       │ mov %rax,-0x38(%rbp) ▒
       │ cmova %rdx,%r14 ▒
       │ test %r14d,%r14d ▒
       │ movslq %r14d,%rdx ▒
       │ ↓ je 93 ▒
       │ xor %eax,%eax ▒
       │ nop ▒
       │ movb $0x0,(%rsi) ▒
 25,00 │ nop
...............................

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: linux-image-4.4.0-28-generic 4.4.0-28.47
ProcVersionSignature: Ubuntu 4.4.0-28.47-generic 4.4.13
Uname: Linux 4.4.0-28-generic x86_64
ApportVersion: 2.20.1-0ubuntu2.1
Architecture: amd64
AudioDevicesInUse:
 USER PID ACCESS COMMAND
 /dev/snd/controlC0: asu 3122 F.... pulseaudio
CurrentDesktop: MATE
Date: Tue Jul 12 22:59:12 2016
InstallationDate: Installed on 2016-04-29 (74 days ago)
InstallationMedia: Ubuntu-Studio 16.04 LTS "Xenial Xerus" - Release amd64 (20160420.1)
IwConfig:
 lo no wireless extensions.

 enp1s0 no wireless extensions.
MachineType: Olidata S.p.A. ALABAMA
ProcFB: 0 inteldrmfb
ProcKernelCmdLine: BOOT_IMAGE=/vmlinuz-4.4.0-28-generic root=/dev/mapper/192--168--0--108--vg-root ro
RelatedPackageVersions:
 linux-restricted-modules-4.4.0-28-generic N/A
 linux-backports-modules-4.4.0-28-generic N/A
 linux-firmware 1.157.2
RfKill:

SourcePackage: linux
UpgradeStatus: No upgrade log present (probably fresh install)
dmi.bios.date: 07/08/2008
dmi.bios.vendor: American Megatrends Inc.
dmi.bios.version: S0101
dmi.board.asset.tag: To Be Filled By O.E.M.
dmi.board.name: To be filled by O.E.M.
dmi.board.vendor: To be filled by O.E.M.
dmi.board.version: To be filled by O.E.M.
dmi.chassis.asset.tag: To Be Filled By O.E.M.
dmi.chassis.type: 3
dmi.chassis.vendor: To Be Filled By O.E.M.
dmi.chassis.version: To Be Filled By O.E.M.
dmi.modalias: dmi:bvnAmericanMegatrendsInc.:bvrS0101:bd07/08/2008:svnOlidataS.p.A.:pnALABAMA:pvrToBeFilledByO.E.M.:rvnTobefilledbyO.E.M.:rnTobefilledbyO.E.M.:rvrTobefilledbyO.E.M.:cvnToBeFilledByO.E.M.:ct3:cvrToBeFilledByO.E.M.:
dmi.product.name: ALABAMA
dmi.product.version: To Be Filled By O.E.M.
dmi.sys.vendor: Olidata S.p.A.