|| ||Ray Bryant <firstname.lastname@example.org>|
|| ||Hirokazu Takahashi <email@example.com>, Andi Kleen <firstname.lastname@example.org>,
Dave Hansen <email@example.com>,
Marcelo Tosatti <firstname.lastname@example.org>|
|| ||[PATCH 2.6.13-rc1 0/11] mm: manual page migration-rc4 -- overview|
|| ||Fri, 1 Jul 2005 15:40:38 -0700 (PDT)|
|| ||Christoph Hellwig <email@example.com>,
linux-mm <firstname.lastname@example.org>, Nathan Scott <email@example.com>,
Ray Bryant <firstname.lastname@example.org>,
email@example.com, Ray Bryant <firstname.lastname@example.org>,
Paul Jackson <email@example.com>, firstname.lastname@example.org|
This is the -rc4 version of the manual page migration facility
that I proposed in February and that was discussed on the
linux-mm mailing list. This overview is relatively short since
the overview is effectively unchanged from what I submitted on
April 6, 2005. For details, see the overview I sent out then at:
For details of the -rc2 version of this patcheset, see:
And the -rc3 version is at:
This patch set differs from the previous patchset in the following:
(1) The previous patch was based on 2.6.12-rc5-mhp1, this patchset
is based on patch-2.6.13-rc1-mhp1-pm.gz from www.sr71.net/patches/
2.6.12 (of the Memory Hotplug project patchset maintained by
(2) Changes suggested by Dave Hansen, Hirokazu Takahashi, and
Andi Kleen have been incorporated into this patchset.
If this patch is acceptable to the Memory Hotplug Team, I'd like
to see it added to the page migration sequence of patches in
the memory hotplug patch.
This patch adds a parameter to try_to_migrate_pages().
The last patch of this series:
Should be inserted in the memory hotplug patcheset after the
patch: N1.1-pass-page_list-to-steal_page.patch to fixup
the call to try_to_migrate_pages() from capture_page_range()
This is the last version of the manual page migration patch
that I will be providing. As of today, Christoph Lameter
(email@example.com), will be responsible for handling this
patchset from an SGI perspective.
Suggestions, flames, etc should be directed to Christoph
at firstname.lastname@example.org. I can also continue to be reached
at email@example.com for discussion of this patchset.
Description of the patches in this patchset
Recall that all of these patches apply to 2.6.13-rc1 with the
page-migration patches applied first. The simplest way to do
this is to obtain the Memory Hotplug broken out patches from
And then to add patches 1-10 of this patchset to the series file
after the patch "AA-PM-99-x86_64-IMMOVABLE.patch". (Patch 11
goes after N1.1-pass-page_list-to-steal_page.patch.) Then apply all
patches up through the 10th patch of this set and turn on the
CONFIG_MEMORY_MIGRATE option. This works on Altix, at least;
that is the only NUMA machine I have access to at the moment.
The 11th patch is only needed if you want to try to build the
entire mhp1 patchset after applying the manual page migration
Patch 1: hirokazu-steal_page_from_lru.patch
This patch (due to Hirokazu Tokahashi) simplifies the interface
to steal_page_from_lru() and is not yet present in the 2.6.12-rc5-mhp1
patchset. Unchanged since -rc3.
Patch 2: xfs-migrate-page-rc4.patch
This patch, due to Nathan Scott at SGI, provides a migrate_
page method for XFS. EXT2 and EXT3 already have such methods.
Unchanged from -rc3.
Patch 3: add-node_map-arg-to-try_to_migrate_pages-rc4.patch
This patch adds an additional argument to try_to_migrate_pages().
The additional argument controls where pages found on specific
nodes in the page_list passed into try_to_migrate_pages() are
migrated to. Unchanged from -rc3.
Patch 4: add-sys_migrate_pages-rc4.patch
This is the patch that adds the migrate_pages() system call.
This patch provides a simple version of the system call that
migrates all pages associated with a particular process, so
is really only useful for programs that are statically linked
(i. e. that don't map in any shared libraries).
The following changes have been made since -rc3:
Suggestions from Dave Hansen and Hirokazu Takahashi
have been incorporated.
Patch 5: sys_migrate_pages-mempolicy-migration-rc4.patch
This patch updates the memory policy data structures
as they are encountered in accordance with the migration
request. Unchanged from -rc3.
Patch 6: This patch is new in -rc4. This patch fixes a problem
with the mempolicy migration code for shared objects.
Andi Kleen pointed out this problem in -rc3.
Patch 7: add-mempolicy-control-rc4.patch
This patch extends the mbind() and get_mempolicy() system
calls to support the interface to override the default
kernel policy. Unchanged from -rc3.
Patch 8: sys_migrate_pages-migration-selection-rc4.patch
This patch uses the migration policy bits set by the code
from the last patch to control which mapped files are
migrated (or not). Unchanged from -rc3.
Patch 9: sys_migrate_pages-cpuset-support-rc4.patch
This patch makes migrate_pages() cooperate better with
cpusets. The following change has been made since -rc3:
The cpuset support has been split out entirely
to kernel/cpuset.c with only a single callout
from sys_migrate_pages(). This makes the
sys_migrate_pages() code cleaner. This change
was inspired by the changes Dave Hansen
Patch 10: sys_migrate_pages-permissions-check.patch
This patch adds a permission check to make sure the
invoking process has the necessary permissions to migrate
the target task. Unchanged from -rc3.
This patch fixes the call to try_to_migrate_pages()
from capture_page_range() in mm/page_alloc.c that
is introduced in the N1.0-memsection_migrate.patch
of the memory hotplug series. Unchanged from -rc3.
(1) This version of migrate_pages() works reliably only when the
process to be migrated has been stopped (e. g., using SIGSTOP)
before the migrate_pages() system call is executed.
(The system doesn't crash or oops, but sometimes the process
being migrated will be "Killed by VM" when it starts up again.
There may be a few messages put into the log as well at that time.)
At the moment, I am proposing that processes need to be
suspended before being migrated. This really should not
be a performance concern, since the delay imposed by page
migration far exceeds any delay imposed by SIGSTOPing the
processes before migration and SIGCONTinuing them afterward.
The problem with this approach is that there is no good way
to enforce this. (i. e. even if the process is stopped at
the start execution of the migrate_pages() system call,
there is no way to ensure it doesn't get started during
execution of the call.)
Christoph Lameter has some ideas about using PF_FREEZE to handle
this problem. I will leave further work in this area to
Christoph. I have provided some sample code to Christoph
to indicate one way to integrate his approach into the existing
page migration code.
(2) I'm still using system call #1279. On ia64 this is the
last slot in the system call table. A system call number
needs to be assigned to migrate_pages().
(3) As part of the discussion with Andi Kleen, we agreed to
provide some memory migration support under MPOL_MF_STRICT.
Currently, if one calls mbind() with the flag MPOL_MF_STRICT
set, and pages are found that don't follow the memory policy,
then the mbind() will return -EIO. Andi would like to be
able cause those pages to be migrated to the correct nodes.
This feature is not yet part of this patchset and will
be added as a distinct set of patches. I'm planning on
providing some sample code to Christoph indicating how
this might be done in the future.
The purpose of this set of patches is to introduce the necessary kernel
infrastructure to support "manual page migration". That phrase is
intended to describe a facility whereby some user program (most likely
a batch scheduler) is given the responsibility of managing where jobs
run on a large NUMA system. If it turns out that a job needs to be
run on a different set of nodes from where it is running now, then that
user program would invoke this facility to move the job to the new set
We use the word "manual" here to indicate that the facility is invoked
in a way that the kernel is told where to move things; we distinguish
this approach from "automatic page migration" facilities which have been
proposed in the past. To us, "automatic page migration" implies using
hardware counters to determine where pages should reside and having the
O/S automatically move misplaced pages. The utility of such facilities,
for example, on IRIX has, been mixed, and we are not currently proposing
such a facility for Linux.
The normal sequence of events would be as follows: A job is running
on, say nodes 5-8, and a higher priority job arrives and the only place
it can be run, for whatever reason, is nodes 5-8. Then the scheduler
would suspend the processes of the existing job (by, for example sending
them a SIGSTOP) and start the new job on those nodes. At some point in
the future, other nodes become available for use, and at this point the
batch scheduler would invoke the manual page migration facility to move
the processes of the suspended job from nodes 5-8 to the new set of nodes.
Note that not all of the pages of all of the processes will need to (or
should) be moved. For example, pages of shared libraries are likely to be
shared by many processes in the system; these pages should not be moved
merely because a few processes using these libraries have been migrated.
As discussed above, the kernel code handles this by migrating all
anonymous VMAs and all VMAs with the VM_WRITE bit set. VMAs that map
the code segments of a program don't have VM_WRITE set, so shared
library code segments will not be migrated (by default). Read-only mapped
files (e. g. files in /usr/lib for National Language support) are also
not migrated by default.
The default migration decisions of the kernel migration code can be
overridden for mmap()'d files using the extensions provided for the
mbind() system call, as described in patches 7 and 8 above. This call
can be used, for example, to cause the program executable to be migrated.
Similarly, if the user has a (non-system) data file mapped R/O, the
mbind() system call can be used to override the kernel default and cause
the mapped file to be migrated as well.
Ray Bryant firstname.lastname@example.org
The box said: "Requires Windows 98 or better",
so I installed Linux.
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