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mm: refactor find_next_best_node to find_next_best_node_in

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Patch series "mm: refactor zonelist constructors and iterators", v3.

find_next_best_node() picks the next-closest node when building a fallback
list, and hardcodes N_MEMORY as the set it picks from.

Refactor it into find_next_best_node_in(), which takes the candidate set
explicitly.

This makes the existing behaviour explicit at both mm/memory-tiers.c call
sites - they select demotion targets in fallback order from N_MEMORY - and
lets callers narrow that set.

Then extract the per-node construction loop out of build_zonelists() into
build_node_zonelist(), parameterised on the candidate nodemask and
destination zonelist index.

Together these allow a zonelist to be built over a candidate set other
than N_MEMORY, into a zonelist other than FALLBACK, and iterated in
fallback order over a caller-defined subset.

These are prerequisites for generating a private node zonelist (nodes
unreachable by default), but are otherwise general improvements to the
existing interfaces so I'm proposing them separately.

No functional change intended - purely refactor commits.


This patch (of 2):

find_next_best_node() picks the next-closest node for a fallback list
from the full N_MEMORY set. Refactor it into find_next_best_node_in(),
which takes an explicit candidates nodemask.

This enables building fallback lists with non-N_MEMORY candidates.

No functional change: every caller still selects from N_MEMORY.

Link: https://lore.kernel.org/20260923022902.2433614-1-gourry@gourry.net
Link: https://lore.kernel.org/20260923022902.2433614-2-gourry@gourry.net
Signed-off-by: Gregory Price <gourry@gourry.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Vlastimil Babka (SUSE) <vbabka@kernel.org>
Acked-by: Balbir Singh <balbirs@nvidia.com>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Reviewed-by: Zenghui Yu (Huawei) <zenghui.yu@linux.dev>
Cc: David Hildenbrand <david@kernel.org>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Mike Rapoport <rppt@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Joshua Hahn <joshua.hahnjy@gmail.com>
Cc: Rakie Kim <rakie.kim@sk.com>
Cc: Ying Huang <ying.huang@linux.alibaba.com>
Cc: Brendan Jackman <brendan.jackman@linux.dev>
Cc: Johannes Weiner <hannes@cmpxchg.org>
This commit is contained in:
Gregory Price 2026-09-22 22:29:01 -04:00 committed by Andrew Morton
parent 0bd719cb60
commit 5436132610
3 changed files with 16 additions and 10 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

6
mm/internal.h
View File

@ -1124,7 +1124,8 @@ extern int node_reclaim_mode;
extern unsigned long node_reclaim(struct pglist_data *pgdat,
gfp_t gfp_mask, unsigned int order);
extern int find_next_best_node(int node, nodemask_t *used_node_mask);
int find_next_best_node_in(int node, nodemask_t *used_node_mask,
const nodemask_t *candidates);
#else
#define node_reclaim_mode 0
@ -1133,7 +1134,8 @@ static inline unsigned long node_reclaim(struct pglist_data *pgdat,
{
return 0;
}
static inline int find_next_best_node(int node, nodemask_t *used_node_mask)
static inline int find_next_best_node_in(int node, nodemask_t *used_node_mask,
const nodemask_t *candidates)
{
return NUMA_NO_NODE;
}

7
mm/memory-tiers.c
View File

@ -370,7 +370,7 @@ int next_demotion_node(int node, const nodemask_t *allowed_mask)
* closest demotion target.
*/
nodes_complement(mask, *allowed_mask);
return find_next_best_node(node, &mask);
return find_next_best_node_in(node, &mask, &node_states[N_MEMORY]);
}
static void disable_all_demotion_targets(void)
@ -450,7 +450,7 @@ static void establish_demotion_targets(void)
memtier = list_next_entry(memtier, list);
tier_nodes = get_memtier_nodemask(memtier);
/*
* find_next_best_node, use 'used' nodemask as a skip list.
* find_next_best_node_in, use 'used' nodemask as a skip list.
* Add all memory nodes except the selected memory tier
* nodelist to skip list so that we find the best node from the
* memtier nodelist.
@ -463,7 +463,8 @@ static void establish_demotion_targets(void)
* in the preferred mask when allocating pages during demotion.
*/
do {
target = find_next_best_node(node, &tier_nodes);
target = find_next_best_node_in(node, &tier_nodes,
&node_states[N_MEMORY]);
if (target == NUMA_NO_NODE)
break;

13
mm/page_alloc.c
View File

@ -5781,9 +5781,10 @@ static int numa_zonelist_order_handler(const struct ctl_table *table, int write,
static int node_load[MAX_NUMNODES];
/**
* find_next_best_node - find the next node that should appear in a given node's fallback list
* find_next_best_node_in - find the next node that should appear in a given node's fallback list
* @node: node whose fallback list we're appending
* @used_node_mask: nodemask_t of already used nodes
* @candidates: nodemask_t of nodes eligible for selection
*
* We use a number of factors to determine which is the next node that should
* appear on a given node's fallback list. The node should not have appeared
@ -5795,7 +5796,8 @@ static int node_load[MAX_NUMNODES];
*
* Return: node id of the found node or %NUMA_NO_NODE if no node is found.
*/
int find_next_best_node(int node, nodemask_t *used_node_mask)
int find_next_best_node_in(int node, nodemask_t *used_node_mask,
const nodemask_t *candidates)
{
int n, val;
int min_val = INT_MAX;
@ -5805,12 +5807,12 @@ int find_next_best_node(int node, nodemask_t *used_node_mask)
* Use the local node if we haven't already, but for memoryless local
* node, we should skip it and fall back to other nodes.
*/
if (!node_isset(node, *used_node_mask) && node_state(node, N_MEMORY)) {
if (!node_isset(node, *used_node_mask) && node_isset(node, *candidates)) {
node_set(node, *used_node_mask);
return node;
}
for_each_node_state(n, N_MEMORY) {
for_each_node_mask(n, *candidates) {
/* Don't want a node to appear more than once */
if (node_isset(n, *used_node_mask))
@ -5895,7 +5897,8 @@ static void build_zonelists(pg_data_t *pgdat)
prev_node = local_node;
memset(node_order, 0, sizeof(node_order));
while ((node = find_next_best_node(local_node, &used_mask)) >= 0) {
while ((node = find_next_best_node_in(local_node, &used_mask,
&node_states[N_MEMORY])) >= 0) {
/*
* We don't want to pressure a particular node.
* So adding penalty to the first node in same