Re: [RFC PATCH 4/4] hugetlb: add support for preferred node to alloc_huge_page_nodemask

[Michal Hocko <mhocko@kernel.org>]

On Thu 08-06-17 10:38:06, Vlastimil Babka wrote:
> On 06/08/2017 09:45 AM, Michal Hocko wrote:
> > From: Michal Hocko <mhocko@suse.com>
> > 
> > alloc_huge_page_nodemask tries to allocate from any numa node in the
> > allowed node mask. This might lead to filling up low NUMA nodes while
> > others are not used. We can reduce this risk by introducing a concept
> > of the preferred node similar to what we have in the regular page
> > allocator. We will start allocating from the preferred nid and then
> > iterate over all allowed nodes until we try them all. Introduce
> > for_each_node_mask_preferred helper which does the iteration and reuse
> > the available preferred node in new_page_nodemask which is currently
> > the only caller of alloc_huge_page_nodemask.
> > 
> > Signed-off-by: Michal Hocko <mhocko@suse.com>
> 
> That's better, yeah. I don't think it would be too hard to use a
> zonelist though. What do others think?

OK, so I've given it a try. This is untested yet but it doesn't look all
that bad. dequeue_huge_page_node will most proably see some clean up on
top but I've kept it for simplicity for now.
---
>From 597ab787ac081b57db13ce5576700163d0c1208c Mon Sep 17 00:00:00 2001
From: Michal Hocko <mhocko@suse.com>
Date: Wed, 7 Jun 2017 10:31:59 +0200
Subject: [PATCH] hugetlb: add support for preferred node to
 alloc_huge_page_nodemask

alloc_huge_page_nodemask tries to allocate from any numa node in the
allowed node mask. This might lead to filling up low NUMA nodes while
others are not used. We can reduce this risk by introducing a concept
of the preferred node similar to what we have in the regular page
allocator. We will start allocating from the preferred nid and then
iterate over all allowed nodes in the zonelist order until we try them
all.

This is mimicking the page allocator logic except it operates on
per-node mempools. dequeue_huge_page_vma already does this so distill
the zonelist logic into a more generic dequeue_huge_page_nodemask
and use it in alloc_huge_page_nodemask.

Signed-off-by: Michal Hocko <mhocko@suse.com>
---
 include/linux/hugetlb.h |   3 +-
 include/linux/migrate.h |   2 +-
 mm/hugetlb.c            | 111 +++++++++++++++++++++++++-----------------------
 3 files changed, 60 insertions(+), 56 deletions(-)

diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
index c469191bb13b..d4c33a8583be 100644
--- a/include/linux/hugetlb.h
+++ b/include/linux/hugetlb.h
@@ -349,7 +349,8 @@ struct page *alloc_huge_page(struct vm_area_struct *vma,
 struct page *alloc_huge_page_node(struct hstate *h, int nid);
 struct page *alloc_huge_page_noerr(struct vm_area_struct *vma,
 				unsigned long addr, int avoid_reserve);
-struct page *alloc_huge_page_nodemask(struct hstate *h, const nodemask_t *nmask);
+struct page *alloc_huge_page_nodemask(struct hstate *h, int preferred_nid,
+				nodemask_t *nmask);
 int huge_add_to_page_cache(struct page *page, struct address_space *mapping,
 			pgoff_t idx);
 
diff --git a/include/linux/migrate.h b/include/linux/migrate.h
index f80c9882403a..af3ccf93efaa 100644
--- a/include/linux/migrate.h
+++ b/include/linux/migrate.h
@@ -38,7 +38,7 @@ static inline struct page *new_page_nodemask(struct page *page, int preferred_ni
 
 	if (PageHuge(page))
 		return alloc_huge_page_nodemask(page_hstate(compound_head(page)),
-				nodemask);
+				preferred_nid, nodemask);
 
 	if (PageHighMem(page)
 	    || (zone_idx(page_zone(page)) == ZONE_MOVABLE))
diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 01c11ceb47d6..bbb3a1a46c64 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -897,29 +897,58 @@ static struct page *dequeue_huge_page_node_exact(struct hstate *h, int nid)
 	return page;
 }
 
-static struct page *dequeue_huge_page_node(struct hstate *h, int nid)
+/* Movability of hugepages depends on migration support. */
+static inline gfp_t htlb_alloc_mask(struct hstate *h)
 {
-	struct page *page;
-	int node;
+	if (hugepages_treat_as_movable || hugepage_migration_supported(h))
+		return GFP_HIGHUSER_MOVABLE;
+	else
+		return GFP_HIGHUSER;
+}
 
-	if (nid != NUMA_NO_NODE)
-		return dequeue_huge_page_node_exact(h, nid);
+static struct page *dequeue_huge_page_nodemask(struct hstate *h, int nid,
+		nodemask_t *nmask)
+{
+	unsigned int cpuset_mems_cookie;
+	struct zonelist *zonelist;
+	struct page *page = NULL;
+	struct zone *zone;
+	struct zoneref *z;
+	gfp_t gfp_mask;
+	int node = -1;
+
+	gfp_mask = htlb_alloc_mask(h);
+	zonelist = node_zonelist(nid, gfp_mask);
+
+retry_cpuset:
+	cpuset_mems_cookie = read_mems_allowed_begin();
+	for_each_zone_zonelist_nodemask(zone, z, zonelist, gfp_zone(gfp_mask), nmask) {
+		if (!cpuset_zone_allowed(zone, gfp_mask))
+			continue;
+		/*
+		 * no need to ask again on the same node. Pool is node rather than
+		 * zone aware
+		 */
+		if (zone_to_nid(zone) == node)
+			continue;
+		node = zone_to_nid(zone);
 
-	for_each_online_node(node) {
 		page = dequeue_huge_page_node_exact(h, node);
 		if (page)
-			return page;
+			break;
 	}
+	if (unlikely(!page && read_mems_allowed_retry(cpuset_mems_cookie)))
+		goto retry_cpuset;
+
 	return NULL;
 }
 
-/* Movability of hugepages depends on migration support. */
-static inline gfp_t htlb_alloc_mask(struct hstate *h)
+static struct page *dequeue_huge_page_node(struct hstate *h, int nid)
 {
-	if (hugepages_treat_as_movable || hugepage_migration_supported(h))
-		return GFP_HIGHUSER_MOVABLE;
-	else
-		return GFP_HIGHUSER;
+	if (nid != NUMA_NO_NODE)
+		return dequeue_huge_page_node_exact(h, nid);
+
+	return dequeue_huge_page_nodemask(h, nid, NULL);
 }
 
 static struct page *dequeue_huge_page_vma(struct hstate *h,
@@ -927,15 +956,10 @@ static struct page *dequeue_huge_page_vma(struct hstate *h,
 				unsigned long address, int avoid_reserve,
 				long chg)
 {
-	struct page *page = NULL;
+	struct page *page;
 	struct mempolicy *mpol;
 	nodemask_t *nodemask;
-	gfp_t gfp_mask;
 	int nid;
-	struct zonelist *zonelist;
-	struct zone *zone;
-	struct zoneref *z;
-	unsigned int cpuset_mems_cookie;
 
 	/*
 	 * A child process with MAP_PRIVATE mappings created by their parent
@@ -950,32 +974,14 @@ static struct page *dequeue_huge_page_vma(struct hstate *h,
 	if (avoid_reserve && h->free_huge_pages - h->resv_huge_pages == 0)
 		goto err;
 
-retry_cpuset:
-	cpuset_mems_cookie = read_mems_allowed_begin();
-	gfp_mask = htlb_alloc_mask(h);
-	nid = huge_node(vma, address, gfp_mask, &mpol, &nodemask);
-	zonelist = node_zonelist(nid, gfp_mask);
-
-	for_each_zone_zonelist_nodemask(zone, z, zonelist,
-						MAX_NR_ZONES - 1, nodemask) {
-		if (cpuset_zone_allowed(zone, gfp_mask)) {
-			page = dequeue_huge_page_node(h, zone_to_nid(zone));
-			if (page) {
-				if (avoid_reserve)
-					break;
-				if (!vma_has_reserves(vma, chg))
-					break;
-
-				SetPagePrivate(page);
-				h->resv_huge_pages--;
-				break;
-			}
-		}
+	nid = huge_node(vma, address, htlb_alloc_mask(h), &mpol, &nodemask);
+	page = dequeue_huge_page_nodemask(h, nid, nodemask);
+	if (page && !(avoid_reserve || (!vma_has_reserves(vma, chg)))) {
+		SetPagePrivate(page);
+		h->resv_huge_pages--;
 	}
 
 	mpol_cond_put(mpol);
-	if (unlikely(!page && read_mems_allowed_retry(cpuset_mems_cookie)))
-		goto retry_cpuset;
 	return page;
 
 err:
@@ -1723,29 +1729,26 @@ struct page *alloc_huge_page_node(struct hstate *h, int nid)
 	return page;
 }
 
-struct page *alloc_huge_page_nodemask(struct hstate *h, const nodemask_t *nmask)
+struct page *alloc_huge_page_nodemask(struct hstate *h, int preferred_nid,
+		nodemask_t *nmask)
 {
 	struct page *page = NULL;
-	int node;
 
 	spin_lock(&hugetlb_lock);
 	if (h->free_huge_pages - h->resv_huge_pages > 0) {
-		for_each_node_mask(node, *nmask) {
-			page = dequeue_huge_page_node_exact(h, node);
-			if (page)
-				break;
-		}
+		page = dequeue_huge_page_nodemask(h, preferred_nid, nmask);
+		if (page)
+			goto unlock;
 	}
+unlock:
 	spin_unlock(&hugetlb_lock);
 	if (page)
 		return page;
 
 	/* No reservations, try to overcommit */
-	for_each_node_mask(node, *nmask) {
-		page = __alloc_buddy_huge_page_no_mpol(h, node);
-		if (page)
-			return page;
-	}
+	page = __alloc_buddy_huge_page_no_mpol(h, preferred_nid);
+	if (page)
+		return page;
 
 	return NULL;
 }
-- 
2.11.0

-- 
Michal Hocko
SUSE Labs