[RFC PATCH v2 1/3] mm/mempolicy: use policy_node helper with MPOL_PREFERRED_MANY

A followup patch will enable setting a home node with MPOL_PREFERRED_MANY
memory policy. To facilitate that switch to using policy_node helper.
There is no functional change in this patch.

Cc: Ben Widawsky <redacted>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Feng Tang <redacted>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Andrea Arcangeli <redacted>
Cc: Mel Gorman <redacted>
Cc: Mike Kravetz <redacted>
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: Vlastimil Babka <redacted>
Cc: Andi Kleen <redacted>
Cc: Dan Williams <redacted>
Cc: Huang Ying <redacted>
Cc: linux-api@vger.kernel.org
Signed-off-by: Aneesh Kumar K.V <redacted>
---
 mm/mempolicy.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 1592b081c58e..6f0f607cd070 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c

@@ -2067,7 +2067,7 @@ static struct page *alloc_pages_preferred_many(gfp_t gfp, unsigned int order,
 	preferred_gfp &= ~(__GFP_DIRECT_RECLAIM | __GFP_NOFAIL);
 	page = __alloc_pages(preferred_gfp, order, nid, &pol->nodes);
 	if (!page)
-		page = __alloc_pages(gfp, order, numa_node_id(), NULL);
+		page = __alloc_pages(gfp, order, nid, NULL);
 
 	return page;
 }

@@ -2108,6 +2108,7 @@ struct page *alloc_pages_vma(gfp_t gfp, int order, struct vm_area_struct *vma,
 	}
 
 	if (pol->mode == MPOL_PREFERRED_MANY) {
+		node = policy_node(gfp, pol, node);
 		page = alloc_pages_preferred_many(gfp, order, node, pol);
 		mpol_cond_put(pol);
 		goto out;

@@ -2192,7 +2193,7 @@ struct page *alloc_pages(gfp_t gfp, unsigned order)
 		page = alloc_page_interleave(gfp, order, interleave_nodes(pol));
 	else if (pol->mode == MPOL_PREFERRED_MANY)
 		page = alloc_pages_preferred_many(gfp, order,
-				numa_node_id(), pol);
+				  policy_node(gfp, pol, numa_node_id()), pol);
 	else
 		page = __alloc_pages(gfp, order,
 				policy_node(gfp, pol, numa_node_id()),

-- 
2.31.1

This syscall can be used to set a home node for the MPOL_BIND
and MPOL_PREFERRED_MANY memory policy. Users should use this
syscall after setting up a memory policy for the specified range
as shown below.

mbind(p, nr_pages * page_size, MPOL_BIND, new_nodes->maskp,
	    new_nodes->size + 1, 0);
sys_set_mempolicy_home_node((unsigned long)p, nr_pages * page_size,
				  home_node, 0);

The syscall allows specifying a home node/preferred node from which kernel
will fulfill memory allocation requests first.

For address range with MPOL_BIND memory policy, if nodemask specifies more
than one node, page allocations will come from the node in the nodemask
with sufficient free memory that is closest to the home node/preferred node.

For MPOL_PREFERRED_MANY if the nodemask specifies more than one node,
page allocation will come from the node in the nodemask with sufficient
free memory that is closest to the home node/preferred node. If there is
not enough memory in all the nodes specified in the nodemask, the allocation
will be attempted from the closest numa node to the home node in the system.

This helps applications to hint at a memory allocation preference node
and fallback to _only_ a set of nodes if the memory is not available
on the preferred node.  Fallback allocation is attempted from the node which is
nearest to the preferred node.

This helps applications to have control on memory allocation numa nodes and
avoids default fallback to slow memory NUMA nodes. For example a system with
NUMA nodes 1,2 and 3 with DRAM memory and 10, 11 and 12 of slow memory

 new_nodes = numa_bitmask_alloc(nr_nodes);

 numa_bitmask_setbit(new_nodes, 1);
 numa_bitmask_setbit(new_nodes, 2);
 numa_bitmask_setbit(new_nodes, 3);

 p = mmap(NULL, nr_pages * page_size, protflag, mapflag, -1, 0);
 mbind(p, nr_pages * page_size, MPOL_BIND, new_nodes->maskp,  new_nodes->size + 1, 0);

 sys_set_mempolicy_home_node(p, nr_pages * page_size, 2, 0);

This will allocate from nodes closer to node 2 and will make sure kernel will
only allocate from nodes 1, 2 and3. Memory will not be allocated from slow memory
nodes 10, 11 and 12

With MPOL_PREFERRED_MANY on the other hand will first try to allocate from the
closest node to node 2 from the node list 1, 2 and 3. If those nodes don't have
enough memory, kernel will allocate from slow memory node 10, 11 and 12 which
ever is closer to node 2.

Cc: Ben Widawsky <redacted>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Feng Tang <redacted>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Andrea Arcangeli <redacted>
Cc: Mel Gorman <redacted>
Cc: Mike Kravetz <redacted>
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: Vlastimil Babka <redacted>
Cc: Andi Kleen <redacted>
Cc: Dan Williams <redacted>
Cc: Huang Ying <redacted>
Cc: linux-api@vger.kernel.org
Signed-off-by: Aneesh Kumar K.V <redacted>
---
 include/linux/mempolicy.h |  1 +
 mm/mempolicy.c            | 54 +++++++++++++++++++++++++++++++++++++++
 2 files changed, 55 insertions(+)

diff --git a/include/linux/mempolicy.h b/include/linux/mempolicy.h
index 4091692bed8c..7a224d11bdd0 100644
--- a/include/linux/mempolicy.h
+++ b/include/linux/mempolicy.h

@@ -47,6 +47,7 @@ struct mempolicy {
 	unsigned short mode; 	/* See MPOL_* above */
 	unsigned short flags;	/* See set_mempolicy() MPOL_F_* above */
 	nodemask_t nodes;	/* interleave/bind/perfer */
+	int home_node;		/* Home node to use for MPOL_BIND and MPOL_PREFERRED_MANY */
 
 	union {
 		nodemask_t cpuset_mems_allowed;	/* relative to these nodes */

diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 6f0f607cd070..20415c9347e0 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c

@@ -296,6 +296,7 @@ static struct mempolicy *mpol_new(unsigned short mode, unsigned short flags,
 	atomic_set(&policy->refcnt, 1);
 	policy->mode = mode;
 	policy->flags = flags;
+	policy->home_node = NUMA_NO_NODE;
 
 	return policy;
 }

@@ -1483,6 +1484,52 @@ static long kernel_mbind(unsigned long start, unsigned long len,
 	return do_mbind(start, len, lmode, mode_flags, &nodes, flags);
 }
 
+SYSCALL_DEFINE4(set_mempolicy_home_node, unsigned long, start, unsigned long, len,
+		unsigned long, home_node, unsigned long, flags)
+{
+	struct mm_struct *mm = current->mm;
+	struct vm_area_struct *vma;
+	struct mempolicy *new;
+	unsigned long vmstart;
+	unsigned long vmend;
+	unsigned long end;
+	int err = -ENOENT;
+
+	if (start & ~PAGE_MASK)
+		return -EINVAL;
+
+	len = (len + PAGE_SIZE - 1) & PAGE_MASK;
+	end = start + len;
+
+	if (end < start)
+		return -EINVAL;
+	if (end == start)
+		return 0;
+	mmap_write_lock(mm);
+	vma = find_vma(mm, start);
+	for (; vma && vma->vm_start < end;  vma = vma->vm_next) {
+
+		vmstart = max(start, vma->vm_start);
+		vmend   = min(end, vma->vm_end);
+		new = mpol_dup(vma_policy(vma));
+		if (IS_ERR(new)) {
+			err = PTR_ERR(new);
+			break;
+		}
+		/*
+		 * Only update home node if there is an existing vma policy
+		 */
+		if (!new)
+			continue;
+		new->home_node = home_node;
+		err = mbind_range(mm, vmstart, vmend, new);
+		if (err)
+			break;
+	}
+	mmap_write_unlock(mm);
+	return err;
+}
+
 SYSCALL_DEFINE6(mbind, unsigned long, start, unsigned long, len,
 		unsigned long, mode, const unsigned long __user *, nmask,
 		unsigned long, maxnode, unsigned int, flags)

@@ -1807,6 +1854,11 @@ static int policy_node(gfp_t gfp, struct mempolicy *policy, int nd)
 		WARN_ON_ONCE(policy->mode == MPOL_BIND && (gfp & __GFP_THISNODE));
 	}
 
+	if ((policy->mode == MPOL_BIND ||
+	     policy->mode == MPOL_PREFERRED_MANY) &&
+	    policy->home_node != NUMA_NO_NODE)
+		return policy->home_node;
+
 	return nd;
 }
 

@@ -2257,6 +2309,8 @@ bool __mpol_equal(struct mempolicy *a, struct mempolicy *b)
 		return false;
 	if (a->flags != b->flags)
 		return false;
+	if (a->home_node != b->home_node)
+		return false;
 	if (mpol_store_user_nodemask(a))
 		if (!nodes_equal(a->w.user_nodemask, b->w.user_nodemask))
 			return false;

-- 
2.31.1

Cc: Ben Widawsky <redacted>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Feng Tang <redacted>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Andrea Arcangeli <redacted>
Cc: Mel Gorman <redacted>
Cc: Mike Kravetz <redacted>
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: Vlastimil Babka <redacted>
Cc: Andi Kleen <redacted>
Cc: Dan Williams <redacted>
Cc: Huang Ying <redacted>
Cc: linux-api@vger.kernel.org
Signed-off-by: Aneesh Kumar K.V <redacted>
---
 arch/alpha/kernel/syscalls/syscall.tbl      | 1 +
 arch/arm/tools/syscall.tbl                  | 1 +
 arch/arm64/include/asm/unistd.h             | 2 +-
 arch/arm64/include/asm/unistd32.h           | 2 ++
 arch/ia64/kernel/syscalls/syscall.tbl       | 1 +
 arch/m68k/kernel/syscalls/syscall.tbl       | 1 +
 arch/microblaze/kernel/syscalls/syscall.tbl | 1 +
 arch/mips/kernel/syscalls/syscall_n32.tbl   | 1 +
 arch/mips/kernel/syscalls/syscall_n64.tbl   | 1 +
 arch/mips/kernel/syscalls/syscall_o32.tbl   | 1 +
 arch/parisc/kernel/syscalls/syscall.tbl     | 1 +
 arch/powerpc/kernel/syscalls/syscall.tbl    | 1 +
 arch/s390/kernel/syscalls/syscall.tbl       | 1 +
 arch/sh/kernel/syscalls/syscall.tbl         | 1 +
 arch/sparc/kernel/syscalls/syscall.tbl      | 1 +
 arch/x86/entry/syscalls/syscall_32.tbl      | 1 +
 arch/x86/entry/syscalls/syscall_64.tbl      | 1 +
 arch/xtensa/kernel/syscalls/syscall.tbl     | 1 +
 include/linux/syscalls.h                    | 3 +++
 include/uapi/asm-generic/unistd.h           | 4 +++-
 kernel/sys_ni.c                             | 1 +
 21 files changed, 26 insertions(+), 2 deletions(-)

diff --git a/arch/alpha/kernel/syscalls/syscall.tbl b/arch/alpha/kernel/syscalls/syscall.tbl
index e4a041cd5715..62b01f28ca3e 100644
--- a/arch/alpha/kernel/syscalls/syscall.tbl
+++ b/arch/alpha/kernel/syscalls/syscall.tbl

@@ -488,3 +488,4 @@
 556	common	landlock_restrict_self		sys_landlock_restrict_self
 # 557 reserved for memfd_secret
 558	common	process_mrelease		sys_process_mrelease
+559	common	set_mempolicy_home_node		sys_ni_syscall

diff --git a/arch/arm/tools/syscall.tbl b/arch/arm/tools/syscall.tbl
index e842209e135d..654d36611510 100644
--- a/arch/arm/tools/syscall.tbl
+++ b/arch/arm/tools/syscall.tbl

@@ -462,3 +462,4 @@
 446	common	landlock_restrict_self		sys_landlock_restrict_self
 # 447 reserved for memfd_secret
 448	common	process_mrelease		sys_process_mrelease
+449	common	set_mempolicy_home_node		sys_set_mempolicy_home_node

diff --git a/arch/arm64/include/asm/unistd.h b/arch/arm64/include/asm/unistd.h
index 3cb206aea3db..6bdb5f5db438 100644
--- a/arch/arm64/include/asm/unistd.h
+++ b/arch/arm64/include/asm/unistd.h

@@ -38,7 +38,7 @@
 #define __ARM_NR_compat_set_tls		(__ARM_NR_COMPAT_BASE + 5)
 #define __ARM_NR_COMPAT_END		(__ARM_NR_COMPAT_BASE + 0x800)
 
-#define __NR_compat_syscalls		449
+#define __NR_compat_syscalls		450
 #endif
 
 #define __ARCH_WANT_SYS_CLONE

diff --git a/arch/arm64/include/asm/unistd32.h b/arch/arm64/include/asm/unistd32.h
index 844f6ae58662..83dc8cc5040c 100644
--- a/arch/arm64/include/asm/unistd32.h
+++ b/arch/arm64/include/asm/unistd32.h

@@ -903,6 +903,8 @@ __SYSCALL(__NR_landlock_add_rule, sys_landlock_add_rule)
 __SYSCALL(__NR_landlock_restrict_self, sys_landlock_restrict_self)
 #define __NR_process_mrelease 448
 __SYSCALL(__NR_process_mrelease, sys_process_mrelease)
+#define __NR_set_mempolicy_home_node 449
+__SYSCALL(__NR_set_mempolicy_home_node, sys_set_mempolicy_home_node)
 
 /*
  * Please add new compat syscalls above this comment and update

diff --git a/arch/ia64/kernel/syscalls/syscall.tbl b/arch/ia64/kernel/syscalls/syscall.tbl
index 6fea1844fb95..c283e041ac2f 100644
--- a/arch/ia64/kernel/syscalls/syscall.tbl
+++ b/arch/ia64/kernel/syscalls/syscall.tbl

@@ -369,3 +369,4 @@
 446	common	landlock_restrict_self		sys_landlock_restrict_self
 # 447 reserved for memfd_secret
 448	common	process_mrelease		sys_process_mrelease
+449	common	set_mempolicy_home_node		sys_set_mempolicy_home_node

diff --git a/arch/m68k/kernel/syscalls/syscall.tbl b/arch/m68k/kernel/syscalls/syscall.tbl
index 7976dff8f879..1306b416ab7f 100644
--- a/arch/m68k/kernel/syscalls/syscall.tbl
+++ b/arch/m68k/kernel/syscalls/syscall.tbl

@@ -448,3 +448,4 @@
 446	common	landlock_restrict_self		sys_landlock_restrict_self
 # 447 reserved for memfd_secret
 448	common	process_mrelease		sys_process_mrelease
+449	common	set_mempolicy_home_node		sys_set_mempolicy_home_node

diff --git a/arch/microblaze/kernel/syscalls/syscall.tbl b/arch/microblaze/kernel/syscalls/syscall.tbl
index 6b0e11362bd2..013c5c84f90c 100644
--- a/arch/microblaze/kernel/syscalls/syscall.tbl
+++ b/arch/microblaze/kernel/syscalls/syscall.tbl

@@ -454,3 +454,4 @@
 446	common	landlock_restrict_self		sys_landlock_restrict_self
 # 447 reserved for memfd_secret
 448	common	process_mrelease		sys_process_mrelease
+449	common	set_mempolicy_home_node		sys_set_mempolicy_home_node

diff --git a/arch/mips/kernel/syscalls/syscall_n32.tbl b/arch/mips/kernel/syscalls/syscall_n32.tbl
index 70e32de2bcaa..fa8fe5553c66 100644
--- a/arch/mips/kernel/syscalls/syscall_n32.tbl
+++ b/arch/mips/kernel/syscalls/syscall_n32.tbl

@@ -387,3 +387,4 @@
 446	n32	landlock_restrict_self		sys_landlock_restrict_self
 # 447 reserved for memfd_secret
 448	n32	process_mrelease		sys_process_mrelease
+449	n32	set_mempolicy_home_node		sys_set_mempolicy_home_node

diff --git a/arch/mips/kernel/syscalls/syscall_n64.tbl b/arch/mips/kernel/syscalls/syscall_n64.tbl
index 1ca7bc337932..3d9826dad90f 100644
--- a/arch/mips/kernel/syscalls/syscall_n64.tbl
+++ b/arch/mips/kernel/syscalls/syscall_n64.tbl

@@ -363,3 +363,4 @@
 446	n64	landlock_restrict_self		sys_landlock_restrict_self
 # 447 reserved for memfd_secret
 448	n64	process_mrelease		sys_process_mrelease
+449	common	set_mempolicy_home_node		sys_set_mempolicy_home_node

diff --git a/arch/mips/kernel/syscalls/syscall_o32.tbl b/arch/mips/kernel/syscalls/syscall_o32.tbl
index a61c35edaa74..132bb673960a 100644
--- a/arch/mips/kernel/syscalls/syscall_o32.tbl
+++ b/arch/mips/kernel/syscalls/syscall_o32.tbl

@@ -436,3 +436,4 @@
 446	o32	landlock_restrict_self		sys_landlock_restrict_self
 # 447 reserved for memfd_secret
 448	o32	process_mrelease		sys_process_mrelease
+449	o32	set_mempolicy_home_node		sys_set_mempolicy_home_node

diff --git a/arch/parisc/kernel/syscalls/syscall.tbl b/arch/parisc/kernel/syscalls/syscall.tbl
index bf751e0732b7..25732a07f29f 100644
--- a/arch/parisc/kernel/syscalls/syscall.tbl
+++ b/arch/parisc/kernel/syscalls/syscall.tbl

@@ -446,3 +446,4 @@
 446	common	landlock_restrict_self		sys_landlock_restrict_self
 # 447 reserved for memfd_secret
 448	common	process_mrelease		sys_process_mrelease
+449	common	set_mempolicy_home_node		sys_set_mempolicy_home_node

diff --git a/arch/powerpc/kernel/syscalls/syscall.tbl b/arch/powerpc/kernel/syscalls/syscall.tbl
index 7bef917cc84e..6b95e0371812 100644
--- a/arch/powerpc/kernel/syscalls/syscall.tbl
+++ b/arch/powerpc/kernel/syscalls/syscall.tbl

@@ -528,3 +528,4 @@
 446	common	landlock_restrict_self		sys_landlock_restrict_self
 # 447 reserved for memfd_secret
 448	common	process_mrelease		sys_process_mrelease
+449 	nospu	set_mempolicy_home_node		sys_set_mempolicy_home_node

diff --git a/arch/s390/kernel/syscalls/syscall.tbl b/arch/s390/kernel/syscalls/syscall.tbl
index df5261e5cfe1..691932966499 100644
--- a/arch/s390/kernel/syscalls/syscall.tbl
+++ b/arch/s390/kernel/syscalls/syscall.tbl

@@ -451,3 +451,4 @@
 446  common	landlock_restrict_self	sys_landlock_restrict_self	sys_landlock_restrict_self
 # 447 reserved for memfd_secret
 448  common	process_mrelease	sys_process_mrelease		sys_process_mrelease
+449  common	set_mempolicy_home_node	sys_set_mempolicy_home_node	sys_set_mempolicy_home_node

diff --git a/arch/sh/kernel/syscalls/syscall.tbl b/arch/sh/kernel/syscalls/syscall.tbl
index 208f131659c5..9cdc7e105e5d 100644
--- a/arch/sh/kernel/syscalls/syscall.tbl
+++ b/arch/sh/kernel/syscalls/syscall.tbl

@@ -451,3 +451,4 @@
 446	common	landlock_restrict_self		sys_landlock_restrict_self
 # 447 reserved for memfd_secret
 448	common	process_mrelease		sys_process_mrelease
+449	common	set_mempolicy_home_node		sys_set_mempolicy_home_node

diff --git a/arch/sparc/kernel/syscalls/syscall.tbl b/arch/sparc/kernel/syscalls/syscall.tbl
index c37764dc764d..d3667c058e51 100644
--- a/arch/sparc/kernel/syscalls/syscall.tbl
+++ b/arch/sparc/kernel/syscalls/syscall.tbl

@@ -494,3 +494,4 @@
 446	common	landlock_restrict_self		sys_landlock_restrict_self
 # 447 reserved for memfd_secret
 448	common	process_mrelease		sys_process_mrelease
+449	common	set_mempolicy_home_node		sys_set_mempolicy_home_node

diff --git a/arch/x86/entry/syscalls/syscall_32.tbl b/arch/x86/entry/syscalls/syscall_32.tbl
index 960a021d543e..85274bd56756 100644
--- a/arch/x86/entry/syscalls/syscall_32.tbl
+++ b/arch/x86/entry/syscalls/syscall_32.tbl

@@ -453,3 +453,4 @@
 446	i386	landlock_restrict_self	sys_landlock_restrict_self
 447	i386	memfd_secret		sys_memfd_secret
 448	i386	process_mrelease	sys_process_mrelease
+449	i386	set_mempolicy_home_node		sys_set_mempolicy_home_node

diff --git a/arch/x86/entry/syscalls/syscall_64.tbl b/arch/x86/entry/syscalls/syscall_64.tbl
index 18b5500ea8bf..b20f43fd95bc 100644
--- a/arch/x86/entry/syscalls/syscall_64.tbl
+++ b/arch/x86/entry/syscalls/syscall_64.tbl

@@ -370,6 +370,7 @@
 446	common	landlock_restrict_self	sys_landlock_restrict_self
 447	common	memfd_secret		sys_memfd_secret
 448	common	process_mrelease	sys_process_mrelease
+449	common	set_mempolicy_home_node	sys_set_mempolicy_home_node
 
 #
 # Due to a historical design error, certain syscalls are numbered differently

diff --git a/arch/xtensa/kernel/syscalls/syscall.tbl b/arch/xtensa/kernel/syscalls/syscall.tbl
index 104b327f8ac9..6879ff2c9c27 100644
--- a/arch/xtensa/kernel/syscalls/syscall.tbl
+++ b/arch/xtensa/kernel/syscalls/syscall.tbl

@@ -419,3 +419,4 @@
 446	common	landlock_restrict_self		sys_landlock_restrict_self
 # 447 reserved for memfd_secret
 448	common	process_mrelease		sys_process_mrelease
+449	common	set_mempolicy_home_node		sys_set_mempolicy_home_node

diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index 252243c7783d..e64d7213d281 100644
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h

@@ -1052,6 +1052,9 @@ asmlinkage long sys_landlock_add_rule(int ruleset_fd, enum landlock_rule_type ru
 		const void __user *rule_attr, __u32 flags);
 asmlinkage long sys_landlock_restrict_self(int ruleset_fd, __u32 flags);
 asmlinkage long sys_memfd_secret(unsigned int flags);
+asmlinkage long sys_set_mempolicy_home_node(unsigned long start, unsigned long len,
+					    unsigned long home_node,
+					    unsigned long flags);
 
 /*
  * Architecture-specific system calls

diff --git a/include/uapi/asm-generic/unistd.h b/include/uapi/asm-generic/unistd.h
index 1c5fb86d455a..c5dd43db8cef 100644
--- a/include/uapi/asm-generic/unistd.h
+++ b/include/uapi/asm-generic/unistd.h

@@ -879,9 +879,11 @@ __SYSCALL(__NR_memfd_secret, sys_memfd_secret)
 #endif
 #define __NR_process_mrelease 448
 __SYSCALL(__NR_process_mrelease, sys_process_mrelease)
+#define __NR_set_mempolicy_home_node 449
+__SYSCALL(__NR_process_mrelease, sys_process_mrelease)
 
 #undef __NR_syscalls
-#define __NR_syscalls 449
+#define __NR_syscalls 450
 
 /*
  * 32 bit systems traditionally used different

diff --git a/kernel/sys_ni.c b/kernel/sys_ni.c
index f43d89d92860..3640d432472c 100644
--- a/kernel/sys_ni.c
+++ b/kernel/sys_ni.c

@@ -296,6 +296,7 @@ COND_SYSCALL(get_mempolicy);
 COND_SYSCALL(set_mempolicy);
 COND_SYSCALL(migrate_pages);
 COND_SYSCALL(move_pages);
+COND_SYSCALL(set_mempolicy_home_node);
 
 COND_SYSCALL(perf_event_open);
 COND_SYSCALL(accept4);

-- 
2.31.1

Hi Aneesh,

On Wed, Oct 20, 2021 at 02:54:52PM +0530, Aneesh Kumar K.V wrote:

This syscall can be used to set a home node for the MPOL_BIND
and MPOL_PREFERRED_MANY memory policy. Users should use this
syscall after setting up a memory policy for the specified range
as shown below.

mbind(p, nr_pages * page_size, MPOL_BIND, new_nodes->maskp,
	    new_nodes->size + 1, 0);
sys_set_mempolicy_home_node((unsigned long)p, nr_pages * page_size,
				  home_node, 0);

The syscall allows specifying a home node/preferred node from which kernel
will fulfill memory allocation requests first.

For address range with MPOL_BIND memory policy, if nodemask specifies more
than one node, page allocations will come from the node in the nodemask
with sufficient free memory that is closest to the home node/preferred node.

For MPOL_PREFERRED_MANY if the nodemask specifies more than one node,
page allocation will come from the node in the nodemask with sufficient
free memory that is closest to the home node/preferred node. If there is
not enough memory in all the nodes specified in the nodemask, the allocation
will be attempted from the closest numa node to the home node in the system.

I can understand the requirement for MPOL_BIND, and for MPOL_PREFERRED_MANY,
it provides 3 levels of preference:
  home node --> preferred nodes --> all nodes
Any real usage cases for this? For a platform which may have 3 types of
memory (HBM, DRAM, PMEM), this may be useful.   

This helps applications to hint at a memory allocation preference node
and fallback to _only_ a set of nodes if the memory is not available
on the preferred node.  Fallback allocation is attempted from the node which is
nearest to the preferred node.

This helps applications to have control on memory allocation numa nodes and
avoids default fallback to slow memory NUMA nodes. For example a system with
NUMA nodes 1,2 and 3 with DRAM memory and 10, 11 and 12 of slow memory

 new_nodes = numa_bitmask_alloc(nr_nodes);

 numa_bitmask_setbit(new_nodes, 1);
 numa_bitmask_setbit(new_nodes, 2);
 numa_bitmask_setbit(new_nodes, 3);

 p = mmap(NULL, nr_pages * page_size, protflag, mapflag, -1, 0);
 mbind(p, nr_pages * page_size, MPOL_BIND, new_nodes->maskp,  new_nodes->size + 1, 0);

 sys_set_mempolicy_home_node(p, nr_pages * page_size, 2, 0);

 
For this example, it's 'mbind + sys_set_mempolicy_home_node', will case
'set_mempolicy + sys_set_mempolicy_home_node' be also supported? 

Thanks,
Feng

This will allocate from nodes closer to node 2 and will make sure kernel will
only allocate from nodes 1, 2 and3. Memory will not be allocated from slow memory
nodes 10, 11 and 12

With MPOL_PREFERRED_MANY on the other hand will first try to allocate from the
closest node to node 2 from the node list 1, 2 and 3. If those nodes don't have
enough memory, kernel will allocate from slow memory node 10, 11 and 12 which
ever is closer to node 2.

[SNIP]

On 10/21/21 13:02, Feng Tang wrote:

Hi Aneesh,

On Wed, Oct 20, 2021 at 02:54:52PM +0530, Aneesh Kumar K.V wrote:

quoted

This syscall can be used to set a home node for the MPOL_BIND
and MPOL_PREFERRED_MANY memory policy. Users should use this
syscall after setting up a memory policy for the specified range
as shown below.

mbind(p, nr_pages * page_size, MPOL_BIND, new_nodes->maskp,
	    new_nodes->size + 1, 0);
sys_set_mempolicy_home_node((unsigned long)p, nr_pages * page_size,
				  home_node, 0);

The syscall allows specifying a home node/preferred node from which kernel
will fulfill memory allocation requests first.

For address range with MPOL_BIND memory policy, if nodemask specifies more
than one node, page allocations will come from the node in the nodemask
with sufficient free memory that is closest to the home node/preferred node.

For MPOL_PREFERRED_MANY if the nodemask specifies more than one node,
page allocation will come from the node in the nodemask with sufficient
free memory that is closest to the home node/preferred node. If there is
not enough memory in all the nodes specified in the nodemask, the allocation
will be attempted from the closest numa node to the home node in the system.

I can understand the requirement for MPOL_BIND, and for MPOL_PREFERRED_MANY,
it provides 3 levels of preference:
   home node --> preferred nodes --> all nodes
Any real usage cases for this? For a platform which may have 3 types of
memory (HBM, DRAM, PMEM), this may be useful.

The patch was based on a need to enable an application (that is already 
using MPOL_PREFERRED to hint a preference node) to run on a system with 
different types of memory (fast and slow memory).

quoted

This helps applications to hint at a memory allocation preference node
and fallback to _only_ a set of nodes if the memory is not available
on the preferred node.  Fallback allocation is attempted from the node which is
nearest to the preferred node.

This helps applications to have control on memory allocation numa nodes and
avoids default fallback to slow memory NUMA nodes. For example a system with
NUMA nodes 1,2 and 3 with DRAM memory and 10, 11 and 12 of slow memory

  new_nodes = numa_bitmask_alloc(nr_nodes);

  numa_bitmask_setbit(new_nodes, 1);
  numa_bitmask_setbit(new_nodes, 2);
  numa_bitmask_setbit(new_nodes, 3);

  p = mmap(NULL, nr_pages * page_size, protflag, mapflag, -1, 0);
  mbind(p, nr_pages * page_size, MPOL_BIND, new_nodes->maskp,  new_nodes->size + 1, 0);

  sys_set_mempolicy_home_node(p, nr_pages * page_size, 2, 0);

  
For this example, it's 'mbind + sys_set_mempolicy_home_node', will case
'set_mempolicy + sys_set_mempolicy_home_node' be also supported?

At this point it is not asked for. Hence the patch is looking up for vma 
policy to set the home node. If there is a need to set home node for a 
task, we can look at adding the same. I have kept flags variable, that 
should help us to accommodate such a request if we get one in the future.

-aneesh