|| ||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 2.6.12-rc3 0/8] mm: manual page migration-rc2 -- overview|
|| ||Tue, 10 May 2005 21:37:56 -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>|
This set of patches is a more or less complete implementation
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:
This patch set differs from the previous patchset in the following:
(1) The previous patch was based on 2.6.12-rc1-mhp3, this patchset
is based on patch-2.6.12-rc3-mhp1-pm.gz from www.sr71.net/patches/
2.6.12 (of the Memory Hotplug project patchset maintained by
(2) This patchset has been divided into a few more, smaller
patches for easier digestion.
(3) This patch set includes a permissions check, whereas the
previous patch set did not. The permissions check is
effectively the following: A process can issue the migrate_pages()
system call against another process if the either (a) the
first process has the permission to send a non-trivial signal
to the second process or if (b) the calling process has the
capability CAP_SYS_ADMIN. See the last patch of this set
(8/8) titled: sys_migrate_pages-permissions-check.patch
for further details.
(4) This patch set includes a patch (again due to Nathan Scott
of SGI) that provides a migrate_page method for XFS.
This patch is necessary to provide acceptable performance
for migrations involving mapped files in XFS. EXT2 and
EXT3 already have migrate_page methods.
(5) Changes suggested by Dave Hansen have been incorporated
into this patch set.
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. (Hirokazu, in particular, could you
review the patches? Thanks.)
As always, suggestions, flames, etc should be directed to me
(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. I am
working on eliminating that restriction, however, at the
present time the system call does not work reliably without
the process first being stopped. (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.)
Of course, I could check to make sure the target process is
stopped in the migrate_pages() system call, but there is no
good way to make sure that the process remains stopped for
the duration of the system call (at least that I am aware
of) so that is a partial fix, at best.
(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) This patch changes adds a parameter to try_to_migrate_pages().
For other calls to try_to_migrate_pages() in the memory hotplug
patch, the additional parameter may be passed in as NULL and
the existing behavior will occur. Later, I'll send out a
patch updates the rest of the memory hotplug patch in accordance
with this change.
(4) system.migration extended attribute support should also be
provided for other file systems. This can be done incrementally.
(5) 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
probably be added as a distinct set of patches.
Description of the patches in this patchset
Recall that all of these patches apply to 2.6.12-rc3 with the
following patch applied first:
In addition, to get things to compile (for Altix), I applied:
and manually added CONFIG_NEED_MULTIPLE_NODES=y to my .config file.
Patch 1: xfs_extended_attributes-rc2.patch
This patch, due to Nathan Scott at SGI, adds support to
XFS for the system.migration extended attribute.
Patch 2: xfs-migrate-page-rc2.patch
This patch, also due to Nathan Scott, provides a migrate_
page method for XFS. EXT2 and EXT3 already have such methods.
Patch 3: add-node_map-arg-to-try_to_migrate_pages-rc2.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
Patch 4: add-sys_migrate_pages-rc2.patch
This is the patch that adds the migrate_pages() system call.
This patch provides is 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).
Patch 5: sys_migrate_pages-xattr-support-rc2.patch
This patch queries the system.migration extended attribute
associated with each mapped file. The result of this query
is used to control which pages are migrated (e. g. if the
extended attribute has the value "libr", then it is assumed
the mapped file is a shared library, and shared pages are
Patch 6: sys_migrate_pages-mempolicy-migration-rc2.patch
This patch updates the memory policy data structures
as they are encountered in accordance with the migration
Patch 7: sys_migrate_pages-cpuset-support.patch
This patch makes migrate_pages() cooperate better with
Patch 8: sys_migrate_pages-permissions-check.patch
This is the permissions check discussed earlier.
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, we use the extended attribute system.migration with
value "lib" to identify such files. If a shared library file does not
have this attribute set, or the shared library is stored in a file system
that does not support extended attributes (e. g. NFS), then the entire
shared library will be migrated.
Ray Bryant email@example.com
The box said: "Requires Windows 98 or better",
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