[Patch] Add tmpfs options for memory placement policies.

[Patch] Add tmpfs options for memory placement policies.

[Robin Holt]

This patch introduces a tmpfs mount option which allows specifying a
memory policy and a second option to specify the nodelist for that policy.
With the default policy, tmpfs will behave as it does today.  This patch
adds support for preferred, bind, and interleave policies.

The default policy will cause pages to be added to tmpfs files on the
node which is doing the writing.  Some jobs expect a single process to
create and manage the tmpfs files.  This results in a node which has a
significantly reduced number of free pages.

With this patch, the administrator can specify the policy and nodes for
that policy where they would prefer allocations.

This patch was originally written by Brent Casavant and Hugh Dickins.
I added support for the bind and preferred policies and the mpol_nodelist
mount option.


Signed-off-by: Brent Casavant <bcasavan@sgi.com>
Signed-off-by: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Robin Holt <holt@sgi.com>

----
Andrew,

Could you add this to the -mm tree?  I am not sure if you do this, but if
there are no complaints with this patch, would you consider pushing it
to Linus before 2.6.16-rc1?

Diffstat output.

 Documentation/filesystems/tmpfs.txt |   12 +++++++++++
 fs/hugetlbfs/inode.c                |    2 -
 include/linux/mempolicy.h           |   11 +++-------
 include/linux/shmem_fs.h            |    2 +
 mm/mempolicy.c                      |   24 ++++++++++++++++++++++
 mm/shmem.c                          |   39 +++++++++++++++++++++++++++++-------
 6 files changed, 75 insertions(+), 15 deletions(-)

Index: linux-2.6/Documentation/filesystems/tmpfs.txt
===================================================================
--- linux-2.6.orig/Documentation/filesystems/tmpfs.txt	2006-01-12 13:03:29.294732378 -0600
+++ linux-2.6/Documentation/filesystems/tmpfs.txt	2006-01-13 06:50:20.727105630 -0600
@@ -78,6 +78,18 @@ use up all the memory on the machine; bu
 that instance in a system with many cpus making intensive use of it.
 
 
+tmpfs has a mount option to set the NUMA memory allocation policy for
+all files in that instance:
+mpol=interleave		prefers to allocate memory from each node in turn
+mpol=default		prefers to allocate memory from the local node
+mpol=bind		prefers to allocate from mpol_nodelist
+mpol=preferred		prefers to allocate from first node in mpol_nodelist
+
+The following mount option is used in conjunction with mpol=interleave,
+mpol=bind or mpol=preferred:
+mpol_nodelist:	nodelist suitable for parsing with nodelist_parse.
+
+
 To specify the initial root directory you can use the following mount
 options:
 
Index: linux-2.6/fs/hugetlbfs/inode.c
===================================================================
--- linux-2.6.orig/fs/hugetlbfs/inode.c	2006-01-12 13:03:29.309379364 -0600
+++ linux-2.6/fs/hugetlbfs/inode.c	2006-01-13 06:58:55.566379423 -0600
@@ -401,7 +401,7 @@ static struct inode *hugetlbfs_get_inode
 		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, MPOL_DEFAULT, NULL);
 		switch (mode & S_IFMT) {
 		default:
 			init_special_inode(inode, mode, dev);
Index: linux-2.6/include/linux/mempolicy.h
===================================================================
--- linux-2.6.orig/include/linux/mempolicy.h	2006-01-12 13:03:29.314261693 -0600
+++ linux-2.6/include/linux/mempolicy.h	2006-01-13 06:38:02.610834339 -0600
@@ -132,12 +132,8 @@ struct shared_policy {
 	spinlock_t lock;
 };
 
-static inline void mpol_shared_policy_init(struct shared_policy *info)
-{
-	info->root = RB_ROOT;
-	spin_lock_init(&info->lock);
-}
-
+void mpol_shared_policy_init(struct shared_policy *info, int policy,
+				nodemask_t *nodes);
 int mpol_set_shared_policy(struct shared_policy *info,
 				struct vm_area_struct *vma,
 				struct mempolicy *new);
@@ -211,7 +207,8 @@ static inline int mpol_set_shared_policy
 	return -EINVAL;
 }
 
-static inline void mpol_shared_policy_init(struct shared_policy *info)
+static inline void mpol_shared_policy_init(struct shared_policy *info,
+					int policy, nodemask_t *nodes)
 {
 }
 
Index: linux-2.6/include/linux/shmem_fs.h
===================================================================
--- linux-2.6.orig/include/linux/shmem_fs.h	2006-01-12 13:03:29.315238158 -0600
+++ linux-2.6/include/linux/shmem_fs.h	2006-01-13 06:29:11.048546866 -0600
@@ -26,6 +26,8 @@ struct shmem_sb_info {
 	unsigned long free_blocks;  /* How many are left for allocation */
 	unsigned long max_inodes;   /* How many inodes are allowed */
 	unsigned long free_inodes;  /* How many are left for allocation */
+	int policy;		    /* Default NUMA memory alloc policy */
+	nodemask_t policy_nodes;    /* nodemask for preferred and bind */
 	spinlock_t    stat_lock;
 };
 
Index: linux-2.6/mm/mempolicy.c
===================================================================
--- linux-2.6.orig/mm/mempolicy.c	2006-01-12 13:03:29.315238158 -0600
+++ linux-2.6/mm/mempolicy.c	2006-01-13 09:16:22.264432446 -0600
@@ -1357,6 +1357,30 @@ restart:
 	return 0;
 }
 
+void mpol_shared_policy_init(struct shared_policy *info, int policy,
+				nodemask_t *policy_nodes)
+{
+	info->root = RB_ROOT;
+	spin_lock_init(&info->lock);
+
+	if (policy != MPOL_DEFAULT) {
+		struct mempolicy *newpol;
+
+		/* Falls back to MPOL_DEFAULT on any error */
+		newpol = mpol_new(policy, policy_nodes);
+		if (!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 = TASK_SIZE;
+			mpol_set_shared_policy(info, &pvma, newpol);
+			mpol_free(newpol);
+		}
+	}
+}
+
 int mpol_set_shared_policy(struct shared_policy *info,
 			struct vm_area_struct *vma, struct mempolicy *npol)
 {
Index: linux-2.6/mm/shmem.c
===================================================================
--- linux-2.6.orig/mm/shmem.c	2006-01-12 13:03:29.315238158 -0600
+++ linux-2.6/mm/shmem.c	2006-01-13 07:08:09.259198432 -0600
@@ -1316,7 +1316,8 @@ shmem_get_inode(struct super_block *sb, 
 		case S_IFREG:
 			inode->i_op = &shmem_inode_operations;
 			inode->i_fop = &shmem_file_operations;
-			mpol_shared_policy_init(&info->policy);
+			mpol_shared_policy_init(&info->policy, sbinfo->policy,
+							&sbinfo->policy_nodes);
 			break;
 		case S_IFDIR:
 			inode->i_nlink++;
@@ -1330,7 +1331,8 @@ shmem_get_inode(struct super_block *sb, 
 			 * Must not load anything in the rbtree,
 			 * mpol_free_shared_policy will not be called.
 			 */
-			mpol_shared_policy_init(&info->policy);
+			mpol_shared_policy_init(&info->policy, MPOL_DEFAULT,
+						NULL);
 			break;
 		}
 	} else if (sbinfo->max_inodes) {
@@ -1843,7 +1845,9 @@ static struct inode_operations shmem_sym
 	.put_link	= shmem_put_link,
 };
 
-static int shmem_parse_options(char *options, int *mode, uid_t *uid, gid_t *gid, unsigned long *blocks, unsigned long *inodes)
+static int shmem_parse_options(char *options, int *mode, uid_t *uid,
+	gid_t *gid, unsigned long *blocks, unsigned long *inodes,
+	int *policy, nodemask_t *policy_nodes)
 {
 	char *this_char, *value, *rest;
 
@@ -1897,6 +1901,19 @@ static int shmem_parse_options(char *opt
 			*gid = simple_strtoul(value,&rest,0);
 			if (*rest)
 				goto bad_val;
+		} else if (!strcmp(this_char,"mpol")) {
+			if (!strcmp(value,"default"))
+				*policy = MPOL_DEFAULT;
+			else if (!strcmp(value,"preferred"))
+				*policy = MPOL_PREFERRED;
+			else if (!strcmp(value,"bind"))
+				*policy = MPOL_BIND;
+			else if (!strcmp(value,"interleave"))
+				*policy = MPOL_INTERLEAVE;
+			else
+				goto bad_val;
+		} else if (!strcmp(this_char,"mpol_nodelist")) {
+			nodelist_parse(value, *policy_nodes);
 		} else {
 			printk(KERN_ERR "tmpfs: Bad mount option %s\n",
 			       this_char);
@@ -1917,12 +1934,14 @@ static int shmem_remount_fs(struct super
 	struct shmem_sb_info *sbinfo = SHMEM_SB(sb);
 	unsigned long max_blocks = sbinfo->max_blocks;
 	unsigned long max_inodes = sbinfo->max_inodes;
+	int policy = sbinfo->policy;
+	nodemask_t policy_nodes = sbinfo->policy_nodes;
 	unsigned long blocks;
 	unsigned long inodes;
 	int error = -EINVAL;
 
-	if (shmem_parse_options(data, NULL, NULL, NULL,
-				&max_blocks, &max_inodes))
+	if (shmem_parse_options(data, NULL, NULL, NULL, &max_blocks,
+				&max_inodes, &policy, &policy_nodes))
 		return error;
 
 	spin_lock(&sbinfo->stat_lock);
@@ -1948,6 +1967,8 @@ static int shmem_remount_fs(struct super
 	sbinfo->free_blocks = max_blocks - blocks;
 	sbinfo->max_inodes  = max_inodes;
 	sbinfo->free_inodes = max_inodes - inodes;
+	sbinfo->policy = policy;
+	sbinfo->policy_nodes = policy_nodes;
 out:
 	spin_unlock(&sbinfo->stat_lock);
 	return error;
@@ -1972,6 +1993,8 @@ static int shmem_fill_super(struct super
 	struct shmem_sb_info *sbinfo;
 	unsigned long blocks = 0;
 	unsigned long inodes = 0;
+	int policy = MPOL_DEFAULT;
+	nodemask_t policy_nodes = node_online_map;
 
 #ifdef CONFIG_TMPFS
 	/*
@@ -1984,8 +2007,8 @@ static int shmem_fill_super(struct super
 		inodes = totalram_pages - totalhigh_pages;
 		if (inodes > blocks)
 			inodes = blocks;
-		if (shmem_parse_options(data, &mode, &uid, &gid,
-					&blocks, &inodes))
+		if (shmem_parse_options(data, &mode, &uid, &gid, &blocks,
+					&inodes, &policy, &policy_nodes))
 			return -EINVAL;
 	}
 #else
@@ -2003,6 +2026,8 @@ static int shmem_fill_super(struct super
 	sbinfo->free_blocks = blocks;
 	sbinfo->max_inodes = inodes;
 	sbinfo->free_inodes = inodes;
+	sbinfo->policy = policy;
+	sbinfo->policy_nodes = policy_nodes;
 
 	sb->s_fs_info = sbinfo;
 	sb->s_maxbytes = SHMEM_MAX_BYTES;

[Patch] Add tmpfs options for memory placement policies (Resend with corrected addresses).

[Robin Holt]

This patch introduces a tmpfs mount option which allows specifying a
memory policy and a second option to specify the nodelist for that policy.
With the default policy, tmpfs will behave as it does today.  This patch
adds support for preferred, bind, and interleave policies.

The default policy will cause pages to be added to tmpfs files on the
node which is doing the writing.  Some jobs expect a single process to
create and manage the tmpfs files.  This results in a node which has a
significantly reduced number of free pages.

With this patch, the administrator can specify the policy and nodes for
that policy where they would prefer allocations.

This patch was originally written by Brent Casavant and Hugh Dickins.
I added support for the bind and preferred policies and the mpol_nodelist
mount option.


Signed-off-by: Brent Casavant <bcasavan@sgi.com>
Signed-off-by: Hugh Dickins <hugh@veritas.com>
Signed-off-by: Robin Holt <holt@sgi.com>

----
Andrew,

Could you add this to the -mm tree?  I am not sure if you do this, but if
there are no complaints with this patch, would you consider pushing it
to Linus before 2.6.16-rc1?

Diffstat output.

 Documentation/filesystems/tmpfs.txt |   12 +++++++++++
 fs/hugetlbfs/inode.c                |    2 -
 include/linux/mempolicy.h           |   11 +++-------
 include/linux/shmem_fs.h            |    2 +
 mm/mempolicy.c                      |   24 ++++++++++++++++++++++
 mm/shmem.c                          |   39 +++++++++++++++++++++++++++++-------
 6 files changed, 75 insertions(+), 15 deletions(-)

Index: linux-2.6/Documentation/filesystems/tmpfs.txt
===================================================================
--- linux-2.6.orig/Documentation/filesystems/tmpfs.txt	2006-01-12 13:03:29.294732378 -0600
+++ linux-2.6/Documentation/filesystems/tmpfs.txt	2006-01-13 06:50:20.727105630 -0600
@@ -78,6 +78,18 @@ use up all the memory on the machine; bu
 that instance in a system with many cpus making intensive use of it.
 
 
+tmpfs has a mount option to set the NUMA memory allocation policy for
+all files in that instance:
+mpol=interleave		prefers to allocate memory from each node in turn
+mpol=default		prefers to allocate memory from the local node
+mpol=bind		prefers to allocate from mpol_nodelist
+mpol=preferred		prefers to allocate from first node in mpol_nodelist
+
+The following mount option is used in conjunction with mpol=interleave,
+mpol=bind or mpol=preferred:
+mpol_nodelist:	nodelist suitable for parsing with nodelist_parse.
+
+
 To specify the initial root directory you can use the following mount
 options:
 
Index: linux-2.6/fs/hugetlbfs/inode.c
===================================================================
--- linux-2.6.orig/fs/hugetlbfs/inode.c	2006-01-12 13:03:29.309379364 -0600
+++ linux-2.6/fs/hugetlbfs/inode.c	2006-01-13 06:58:55.566379423 -0600
@@ -401,7 +401,7 @@ static struct inode *hugetlbfs_get_inode
 		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, MPOL_DEFAULT, NULL);
 		switch (mode & S_IFMT) {
 		default:
 			init_special_inode(inode, mode, dev);
Index: linux-2.6/include/linux/mempolicy.h
===================================================================
--- linux-2.6.orig/include/linux/mempolicy.h	2006-01-12 13:03:29.314261693 -0600
+++ linux-2.6/include/linux/mempolicy.h	2006-01-13 06:38:02.610834339 -0600
@@ -132,12 +132,8 @@ struct shared_policy {
 	spinlock_t lock;
 };
 
-static inline void mpol_shared_policy_init(struct shared_policy *info)
-{
-	info->root = RB_ROOT;
-	spin_lock_init(&info->lock);
-}
-
+void mpol_shared_policy_init(struct shared_policy *info, int policy,
+				nodemask_t *nodes);
 int mpol_set_shared_policy(struct shared_policy *info,
 				struct vm_area_struct *vma,
 				struct mempolicy *new);
@@ -211,7 +207,8 @@ static inline int mpol_set_shared_policy
 	return -EINVAL;
 }
 
-static inline void mpol_shared_policy_init(struct shared_policy *info)
+static inline void mpol_shared_policy_init(struct shared_policy *info,
+					int policy, nodemask_t *nodes)
 {
 }
 
Index: linux-2.6/include/linux/shmem_fs.h
===================================================================
--- linux-2.6.orig/include/linux/shmem_fs.h	2006-01-12 13:03:29.315238158 -0600
+++ linux-2.6/include/linux/shmem_fs.h	2006-01-13 06:29:11.048546866 -0600
@@ -26,6 +26,8 @@ struct shmem_sb_info {
 	unsigned long free_blocks;  /* How many are left for allocation */
 	unsigned long max_inodes;   /* How many inodes are allowed */
 	unsigned long free_inodes;  /* How many are left for allocation */
+	int policy;		    /* Default NUMA memory alloc policy */
+	nodemask_t policy_nodes;    /* nodemask for preferred and bind */
 	spinlock_t    stat_lock;
 };
 
Index: linux-2.6/mm/mempolicy.c
===================================================================
--- linux-2.6.orig/mm/mempolicy.c	2006-01-12 13:03:29.315238158 -0600
+++ linux-2.6/mm/mempolicy.c	2006-01-13 09:16:22.264432446 -0600
@@ -1357,6 +1357,30 @@ restart:
 	return 0;
 }
 
+void mpol_shared_policy_init(struct shared_policy *info, int policy,
+				nodemask_t *policy_nodes)
+{
+	info->root = RB_ROOT;
+	spin_lock_init(&info->lock);
+
+	if (policy != MPOL_DEFAULT) {
+		struct mempolicy *newpol;
+
+		/* Falls back to MPOL_DEFAULT on any error */
+		newpol = mpol_new(policy, policy_nodes);
+		if (!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 = TASK_SIZE;
+			mpol_set_shared_policy(info, &pvma, newpol);
+			mpol_free(newpol);
+		}
+	}
+}
+
 int mpol_set_shared_policy(struct shared_policy *info,
 			struct vm_area_struct *vma, struct mempolicy *npol)
 {
Index: linux-2.6/mm/shmem.c
===================================================================
--- linux-2.6.orig/mm/shmem.c	2006-01-12 13:03:29.315238158 -0600
+++ linux-2.6/mm/shmem.c	2006-01-13 07:08:09.259198432 -0600
@@ -1316,7 +1316,8 @@ shmem_get_inode(struct super_block *sb, 
 		case S_IFREG:
 			inode->i_op = &shmem_inode_operations;
 			inode->i_fop = &shmem_file_operations;
-			mpol_shared_policy_init(&info->policy);
+			mpol_shared_policy_init(&info->policy, sbinfo->policy,
+							&sbinfo->policy_nodes);
 			break;
 		case S_IFDIR:
 			inode->i_nlink++;
@@ -1330,7 +1331,8 @@ shmem_get_inode(struct super_block *sb, 
 			 * Must not load anything in the rbtree,
 			 * mpol_free_shared_policy will not be called.
 			 */
-			mpol_shared_policy_init(&info->policy);
+			mpol_shared_policy_init(&info->policy, MPOL_DEFAULT,
+						NULL);
 			break;
 		}
 	} else if (sbinfo->max_inodes) {
@@ -1843,7 +1845,9 @@ static struct inode_operations shmem_sym
 	.put_link	= shmem_put_link,
 };
 
-static int shmem_parse_options(char *options, int *mode, uid_t *uid, gid_t *gid, unsigned long *blocks, unsigned long *inodes)
+static int shmem_parse_options(char *options, int *mode, uid_t *uid,
+	gid_t *gid, unsigned long *blocks, unsigned long *inodes,
+	int *policy, nodemask_t *policy_nodes)
 {
 	char *this_char, *value, *rest;
 
@@ -1897,6 +1901,19 @@ static int shmem_parse_options(char *opt
 			*gid = simple_strtoul(value,&rest,0);
 			if (*rest)
 				goto bad_val;
+		} else if (!strcmp(this_char,"mpol")) {
+			if (!strcmp(value,"default"))
+				*policy = MPOL_DEFAULT;
+			else if (!strcmp(value,"preferred"))
+				*policy = MPOL_PREFERRED;
+			else if (!strcmp(value,"bind"))
+				*policy = MPOL_BIND;
+			else if (!strcmp(value,"interleave"))
+				*policy = MPOL_INTERLEAVE;
+			else
+				goto bad_val;
+		} else if (!strcmp(this_char,"mpol_nodelist")) {
+			nodelist_parse(value, *policy_nodes);
 		} else {
 			printk(KERN_ERR "tmpfs: Bad mount option %s\n",
 			       this_char);
@@ -1917,12 +1934,14 @@ static int shmem_remount_fs(struct super
 	struct shmem_sb_info *sbinfo = SHMEM_SB(sb);
 	unsigned long max_blocks = sbinfo->max_blocks;
 	unsigned long max_inodes = sbinfo->max_inodes;
+	int policy = sbinfo->policy;
+	nodemask_t policy_nodes = sbinfo->policy_nodes;
 	unsigned long blocks;
 	unsigned long inodes;
 	int error = -EINVAL;
 
-	if (shmem_parse_options(data, NULL, NULL, NULL,
-				&max_blocks, &max_inodes))
+	if (shmem_parse_options(data, NULL, NULL, NULL, &max_blocks,
+				&max_inodes, &policy, &policy_nodes))
 		return error;
 
 	spin_lock(&sbinfo->stat_lock);
@@ -1948,6 +1967,8 @@ static int shmem_remount_fs(struct super
 	sbinfo->free_blocks = max_blocks - blocks;
 	sbinfo->max_inodes  = max_inodes;
 	sbinfo->free_inodes = max_inodes - inodes;
+	sbinfo->policy = policy;
+	sbinfo->policy_nodes = policy_nodes;
 out:
 	spin_unlock(&sbinfo->stat_lock);
 	return error;
@@ -1972,6 +1993,8 @@ static int shmem_fill_super(struct super
 	struct shmem_sb_info *sbinfo;
 	unsigned long blocks = 0;
 	unsigned long inodes = 0;
+	int policy = MPOL_DEFAULT;
+	nodemask_t policy_nodes = node_online_map;
 
 #ifdef CONFIG_TMPFS
 	/*
@@ -1984,8 +2007,8 @@ static int shmem_fill_super(struct super
 		inodes = totalram_pages - totalhigh_pages;
 		if (inodes > blocks)
 			inodes = blocks;
-		if (shmem_parse_options(data, &mode, &uid, &gid,
-					&blocks, &inodes))
+		if (shmem_parse_options(data, &mode, &uid, &gid, &blocks,
+					&inodes, &policy, &policy_nodes))
 			return -EINVAL;
 	}
 #else
@@ -2003,6 +2026,8 @@ static int shmem_fill_super(struct super
 	sbinfo->free_blocks = blocks;
 	sbinfo->max_inodes = inodes;
 	sbinfo->free_inodes = inodes;
+	sbinfo->policy = policy;
+	sbinfo->policy_nodes = policy_nodes;
 
 	sb->s_fs_info = sbinfo;
 	sb->s_maxbytes = SHMEM_MAX_BYTES;

Re: [Patch] Add tmpfs options for memory placement policies (Resend with corrected addresses).

[Andrew Morton]

Robin Holt <holt@sgi.com> wrote:
>
> This patch introduces a tmpfs mount option which allows specifying a
>  memory policy and a second option to specify the nodelist for that policy.
>  With the default policy, tmpfs will behave as it does today.  This patch
>  adds support for preferred, bind, and interleave policies.
> 
>  The default policy will cause pages to be added to tmpfs files on the
>  node which is doing the writing.  Some jobs expect a single process to
>  create and manage the tmpfs files.  This results in a node which has a
>  significantly reduced number of free pages.
> 
>  With this patch, the administrator can specify the policy and nodes for
>  that policy where they would prefer allocations.

Confused.  Is this for applications which cannot be taught to use the
mempolicy API?

Re: [Patch] Add tmpfs options for memory placement policies (Resend with corrected addresses).

[Brent Casavant]

On Fri, 13 Jan 2006, Andrew Morton wrote:

> Confused.  Is this for applications which cannot be taught to use the
> mempolicy API?

In general yes.  Anything that writes into a tmpfs filesystem is liable
to disproportionately decrease the available memory on a particular node.
Since there's no telling what sort of application (e.g. dd/cp/cat) might be
dropping large files there, this lets the admin choose the appropriate
default behavior for their site's situation.

Brent

-- 
Brent Casavant                          All music is folk music.  I ain't
bcasavan@sgi.com                        never heard a horse sing a song.
Silicon Graphics, Inc.                    -- Louis Armstrong

Re: [Patch] Add tmpfs options for memory placement policies (Resend with corrected addresses).

[Hugh Dickins]

On Fri, 13 Jan 2006, Brent Casavant wrote:
> On Fri, 13 Jan 2006, Andrew Morton wrote:
> 
> > Confused.  Is this for applications which cannot be taught to use the
> > mempolicy API?
> 
> In general yes.  Anything that writes into a tmpfs filesystem is liable
> to disproportionately decrease the available memory on a particular node.
> Since there's no telling what sort of application (e.g. dd/cp/cat) might be
> dropping large files there, this lets the admin choose the appropriate
> default behavior for their site's situation.

I look at it differently, and would answer Andrew's question with "no"
rather than "yes".  The mempolicy API applies only to userspace mappings:
so it covers shared memory fine, but cannot be applied to tmpfs files.
Whereas mount's mpol= applies to tmpfs files, and (unfortunately?) cannot
be applied to shm (since that's on an internal mount with no options).

The only overlap comes when a tmpfs file is mmap'ed: then it's possible
to apply the mempolicy API to it, and refine what mount's mpol= defined.
There's been talk in the past of mempolicy for pagecache, which would
also allow mount's mpol= to be refined per file; but that's not appeared.

Hugh