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Subject[PATCH] Use MPOL_INTERLEAVE for tmpfs files
Hello,

This patch causes memory allocation for tmpfs files to be distributed
evenly across NUMA machines. In most circumstances today, tmpfs files
will be allocated on the same node as the task writing to the file.
In many cases, particularly when large files are created, or a large
number of files are created by a single task, this leads to a severe
imbalance in free memory amongst nodes. This patch corrects that
situation.

Memory imbalances such as this can degrade performance in various ways.
The two most typical situations are:

1. An HPC application with tighty synchronized threads has one or more
of its tasks running on a node with little free memory. These
tasks are forced to allocate and/or access memory from remote
nodes. Since access to remote memory incurs a performance penalty,
these threads run slower than those on other nodes. The threads
on other nodes end up waiting for the slower threads (i.e. the
whole application runs only as fast as the slowest thread), thereby
incurring a significant performance penalty for the application.
2. Many seperate tasks access a given file. Since the memory is remote
for almost all processors, this causes a slowdown for the remote
tasks. A small performance gain can be seen by distribute the
file's memory allocation across the system. This scenario has an
additional effect of increasing the memory traffic for the node
hosting the allocation, thereby unfairly penalizing the memory
bandwidth on the host node when such traffic could be spread more
evenly across the machine.

This patch builds upon the NUMA memory policy code. It affects only
the default placement of tmpfs file allocations, and in particular
does not affect /dev/zero memory allocations, which are implemented
in the same code. /dev/zero mappings are typically of interest only
to a particular process, and thus benefit more from local allocations.
In any case, the NUMA API can still be used to more precisely lay out
allocations if so desired, it is only the default behavior of the
allocations which is changed.

System V shared memory allocations are also unaffected, though implemented
by the same code. While in theory these allocations could suffer some
of the same problems as tmpfs files (i.e. a need to distribute large
allocations machine-wide, particularly if the allocation is long-lived),
SGI has not seen this to be a significant problem in practice. As
addressing shm would add to the complexity of the patch with little
perceived value, changes thereto have not been implemented.

The following output (gleaned from /sys/devices/system/node/*/meminfo),
illustrates the effect of this patch. The tmpfs file was created via
the command 'dd if=/dev/zero of=3G bs=1073741824 count=3' within a
tmpfs directory.
Without patch
=============
Before creating 3GB tmpfs file
------------------------------
Nid MemTotal MemFree MemUsed (in kB)
0 4002480 3787040 215440
1 4014080 3942368 71712
2 3882992 3749376 133616
3 3883008 3824288 58720
4 3882992 3825824 57168
5 3883008 3825440 57568
6 3883008 3304576 578432
7 3882992 3829408 53584
8 933888 873696 60192
9 933888 887424 46464
10 933872 890720 43152
11 933888 891328 42560
12 933888 890464 43424
13 933888 880608 53280
14 933872 889408 44464
15 915696 872672 43024
ToT 38767440 37164640 1602800
After creating 3GB tmpfs file
-----------------------------
Nid MemTotal MemFree MemUsed (in kB)
0 4002480 633792 3368688
1 4014080 3938944 75136
2 3882992 3742624 140368
3 3883008 3824288 58720
4 3882992 3825792 57200
5 3883008 3825440 57568
6 3883008 3304640 578368
7 3882992 3829408 53584
8 933888 873696 60192
9 933888 887552 46336
10 933872 890720 43152
11 933888 891264 42624
12 933888 890464 43424
13 933888 880672 53216
14 933872 889408 44464
15 915696 872672 43024
ToT 38767440 34001376 4766064
With patch
==========
Before creating 3GB tmpfs file
------------------------------
Nid MemTotal MemFree MemUsed (in kB)
0 4002496 3263584 738912
1 4014080 3934656 79424
2 3882992 3735584 147408
3 3883008 3815648 67360
4 3882992 3820640 62352
5 3883008 3816992 66016
6 3883008 3803904 79104
7 3882992 3820000 62992
8 933888 872160 61728
9 933888 881888 52000
10 933872 881376 52496
11 933888 883072 50816
12 933888 884000 49888
13 933888 878144 55744
14 933872 875008 58864
15 915696 864256 51440
ToT 38767456 37030912 1736544
After creating 3GB tmpfs file
-----------------------------
Nid MemTotal MemFree MemUsed (in kB)
0 4002496 3066144 936352
1 4014080 3738176 275904
2 3882992 3536800 346192
3 3883008 3619232 263776
4 3882992 3624224 258768
5 3883008 3620576 262432
6 3883008 3607488 275520
7 3882992 3623584 259408
8 933888 675744 258144
9 933888 685472 248416
10 933872 684960 248912
11 933888 686656 247232
12 933888 687584 246304
13 933888 681728 252160
14 933872 678656 255216
15 915696 667840 247856
ToT 38767456 33884864 4882592
Note that in all cases shown above, there are additional sources of
memory imbalances. These do not lie within tmpfs, and will be addressed
in due course.

And now, for your viewing pleasure...

Signed-off-by: Brent Casavant <bcasavan@sgi.com>

Index: linux/mm/mempolicy.c
===================================================================
--- linux.orig/mm/mempolicy.c 2004-11-01 13:47:00.000000000 -0600
+++ linux/mm/mempolicy.c 2004-11-01 15:04:30.000000000 -0600
@@ -1027,6 +1027,28 @@
return 0;
}

+void mpol_shared_policy_init(struct shared_policy *info, unsigned interleave)
+{
+ info->root = RB_ROOT;
+ init_MUTEX(&info->sem);
+
+ if (unlikely(interleave)) {
+ struct mempolicy *newpol;
+
+ /* Falls back to MPOL_DEFAULT on any error */
+ newpol = mpol_new(MPOL_INTERLEAVE, nodes_addr(node_online_map));
+ if (likely(!IS_ERR(newpol))) {
+ /* Create pseudo-vma that contains just the policy */
+ struct vm_area_struct pvma;
+
+ memset(&pvma, 0, sizeof(struct vm_area_struct));
+ /* Policy covers entire file */
+ pvma.vm_end = ~0UL;
+ mpol_set_shared_policy(info, &pvma, newpol);
+ }
+ }
+}
+
int mpol_set_shared_policy(struct shared_policy *info,
struct vm_area_struct *vma, struct mempolicy *npol)
{
Index: linux/fs/hugetlbfs/inode.c
===================================================================
--- linux.orig/fs/hugetlbfs/inode.c 2004-10-18 16:55:07.000000000 -0500
+++ linux/fs/hugetlbfs/inode.c 2004-11-01 14:18:36.000000000 -0600
@@ -384,7 +384,7 @@
inode->i_mapping->backing_dev_info =&hugetlbfs_backing_dev_info;
inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;
info = HUGETLBFS_I(inode);
- mpol_shared_policy_init(&info->policy);
+ mpol_shared_policy_init(&info->policy, 0);
switch (mode & S_IFMT) {
default:
init_special_inode(inode, mode, dev);
Index: linux/include/linux/mempolicy.h
===================================================================
--- linux.orig/include/linux/mempolicy.h 2004-10-18 16:53:10.000000000 -0500
+++ linux/include/linux/mempolicy.h 2004-11-01 14:20:54.000000000 -0600
@@ -137,11 +137,7 @@
struct semaphore sem;
};

-static inline void mpol_shared_policy_init(struct shared_policy *info)
-{
- info->root = RB_ROOT;
- init_MUTEX(&info->sem);
-}
+void mpol_shared_policy_init(struct shared_policy *info, unsigned interleave);

int mpol_set_shared_policy(struct shared_policy *info,
struct vm_area_struct *vma,
@@ -198,7 +194,8 @@
return -EINVAL;
}

-static inline void mpol_shared_policy_init(struct shared_policy *info)
+static inline void mpol_shared_policy_init(struct shared_policy *info,
+ unsigned interleave)
{
}

Index: linux/mm/shmem.c
===================================================================
--- linux.orig/mm/shmem.c 2004-11-01 13:47:00.000000000 -0600
+++ linux/mm/shmem.c 2004-11-01 14:21:43.000000000 -0600
@@ -1236,7 +1236,7 @@
info = SHMEM_I(inode);
memset(info, 0, (char *)inode - (char *)info);
spin_lock_init(&info->lock);
- mpol_shared_policy_init(&info->policy);
+ mpol_shared_policy_init(&info->policy, sbinfo ? 1 : 0);
INIT_LIST_HEAD(&info->swaplist);

switch (mode & S_IFMT) {
--
Brent Casavant bcasavan@sgi.com Forget bright-eyed and
Operating System Engineer http://www.sgi.com/ bushy-tailed; I'm red-
Silicon Graphics, Inc. 44.8562N 93.1355W 860F eyed and bushy-haired.
-
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