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Mon, 13 Oct 2025 12:08:14 -0700 (PDT) From: Joshua Hahn To: Andrew Morton Cc: Chris Mason , Kiryl Shutsemau , "Liam R. Howlett" , Brendan Jackman , David Hildenbrand , Johannes Weiner , Lorenzo Stoakes , Michal Hocko , Mike Rapoport , Suren Baghdasaryan , Vlastimil Babka , Zi Yan , linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: [PATCH v4 1/3] mm/page_alloc/vmstat: Simplify refresh_cpu_vm_stats change detection Date: Mon, 13 Oct 2025 12:08:09 -0700 Message-ID: <20251013190812.787205-2-joshua.hahnjy@gmail.com> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20251013190812.787205-1-joshua.hahnjy@gmail.com> References: <20251013190812.787205-1-joshua.hahnjy@gmail.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Rspamd-Queue-Id: 88488140005 X-Rspamd-Server: rspam11 X-Rspam-User: X-Stat-Signature: c8fbuswk7d8bwt3ffj4x1pn8rcpds6iu X-HE-Tag: 1760382495-638638 X-HE-Meta: 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 Spx07llF 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Currently, refresh_cpu_vm_stats returns an int, indicating how many changes were made during its updates. Using this information, callers like vmstat_update can heuristically determine if more work will be done in the future. However, all of refresh_cpu_vm_stats's callers either (a) ignore the result, only caring about performing the updates, or (b) only care about whether changes were made, but not *how many* changes were made. Simplify the code by returning a bool instead to indicate if updates were made. In addition, simplify fold_diff and decay_pcp_high to return a bool for the same reason. Reviewed-by: Vlastimil Babka Reviewed-by: SeongJae Park Signed-off-by: Joshua Hahn --- include/linux/gfp.h | 2 +- mm/page_alloc.c | 8 ++++---- mm/vmstat.c | 28 +++++++++++++++------------- 3 files changed, 20 insertions(+), 18 deletions(-) diff --git a/include/linux/gfp.h b/include/linux/gfp.h index 0ceb4e09306c..f46b066c7661 100644 --- a/include/linux/gfp.h +++ b/include/linux/gfp.h @@ -386,7 +386,7 @@ extern void free_pages(unsigned long addr, unsigned int order); #define free_page(addr) free_pages((addr), 0) void page_alloc_init_cpuhp(void); -int decay_pcp_high(struct zone *zone, struct per_cpu_pages *pcp); +bool decay_pcp_high(struct zone *zone, struct per_cpu_pages *pcp); void drain_zone_pages(struct zone *zone, struct per_cpu_pages *pcp); void drain_all_pages(struct zone *zone); void drain_local_pages(struct zone *zone); diff --git a/mm/page_alloc.c b/mm/page_alloc.c index 600d9e981c23..bbc3282fdffc 100644 --- a/mm/page_alloc.c +++ b/mm/page_alloc.c @@ -2557,10 +2557,10 @@ static int rmqueue_bulk(struct zone *zone, unsigned int order, * Called from the vmstat counter updater to decay the PCP high. * Return whether there are addition works to do. */ -int decay_pcp_high(struct zone *zone, struct per_cpu_pages *pcp) +bool decay_pcp_high(struct zone *zone, struct per_cpu_pages *pcp) { int high_min, to_drain, batch; - int todo = 0; + bool todo = false; high_min = READ_ONCE(pcp->high_min); batch = READ_ONCE(pcp->batch); @@ -2573,7 +2573,7 @@ int decay_pcp_high(struct zone *zone, struct per_cpu_pages *pcp) pcp->high = max3(pcp->count - (batch << CONFIG_PCP_BATCH_SCALE_MAX), pcp->high - (pcp->high >> 3), high_min); if (pcp->high > high_min) - todo++; + todo = true; } to_drain = pcp->count - pcp->high; @@ -2581,7 +2581,7 @@ int decay_pcp_high(struct zone *zone, struct per_cpu_pages *pcp) spin_lock(&pcp->lock); free_pcppages_bulk(zone, to_drain, pcp, 0); spin_unlock(&pcp->lock); - todo++; + todo = true; } return todo; diff --git a/mm/vmstat.c b/mm/vmstat.c index bb09c032eecf..98855f31294d 100644 --- a/mm/vmstat.c +++ b/mm/vmstat.c @@ -771,25 +771,25 @@ EXPORT_SYMBOL(dec_node_page_state); /* * Fold a differential into the global counters. - * Returns the number of counters updated. + * Returns whether counters were updated. */ static int fold_diff(int *zone_diff, int *node_diff) { int i; - int changes = 0; + bool changed = false; for (i = 0; i < NR_VM_ZONE_STAT_ITEMS; i++) if (zone_diff[i]) { atomic_long_add(zone_diff[i], &vm_zone_stat[i]); - changes++; + changed = true; } for (i = 0; i < NR_VM_NODE_STAT_ITEMS; i++) if (node_diff[i]) { atomic_long_add(node_diff[i], &vm_node_stat[i]); - changes++; + changed = true; } - return changes; + return changed; } /* @@ -806,16 +806,16 @@ static int fold_diff(int *zone_diff, int *node_diff) * with the global counters. These could cause remote node cache line * bouncing and will have to be only done when necessary. * - * The function returns the number of global counters updated. + * The function returns whether global counters were updated. */ -static int refresh_cpu_vm_stats(bool do_pagesets) +static bool refresh_cpu_vm_stats(bool do_pagesets) { struct pglist_data *pgdat; struct zone *zone; int i; int global_zone_diff[NR_VM_ZONE_STAT_ITEMS] = { 0, }; int global_node_diff[NR_VM_NODE_STAT_ITEMS] = { 0, }; - int changes = 0; + bool changed = false; for_each_populated_zone(zone) { struct per_cpu_zonestat __percpu *pzstats = zone->per_cpu_zonestats; @@ -839,7 +839,8 @@ static int refresh_cpu_vm_stats(bool do_pagesets) if (do_pagesets) { cond_resched(); - changes += decay_pcp_high(zone, this_cpu_ptr(pcp)); + if (decay_pcp_high(zone, this_cpu_ptr(pcp))) + changed = true; #ifdef CONFIG_NUMA /* * Deal with draining the remote pageset of this @@ -861,13 +862,13 @@ static int refresh_cpu_vm_stats(bool do_pagesets) } if (__this_cpu_dec_return(pcp->expire)) { - changes++; + changed = true; continue; } if (__this_cpu_read(pcp->count)) { drain_zone_pages(zone, this_cpu_ptr(pcp)); - changes++; + changed = true; } #endif } @@ -887,8 +888,9 @@ static int refresh_cpu_vm_stats(bool do_pagesets) } } - changes += fold_diff(global_zone_diff, global_node_diff); - return changes; + if (fold_diff(global_zone_diff, global_node_diff)) + changed = true; + return changed; } /* -- 2.47.3