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Mon, 15 May 2023 15:02:17 -0300 (-03) Message-ID: <20230515180138.617500477@redhat.com> User-Agent: quilt/0.67 Date: Mon, 15 May 2023 15:00:23 -0300 From: Marcelo Tosatti To: Christoph Lameter Cc: Aaron Tomlin , Frederic Weisbecker , Andrew Morton , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Russell King , Huacai Chen , Heiko Carstens , x86@kernel.org, Vlastimil Babka , Michal Hocko , Marcelo Tosatti Subject: [PATCH v8 08/13] mm/vmstat: switch counter modification to cmpxchg References: <20230515180015.016409657@redhat.com> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 3.1 on 10.11.54.7 X-Stat-Signature: 8dtpd6zsb7bapo6fbf35bwrz719ie748 X-Rspamd-Server: rspam05 X-Rspamd-Queue-Id: 5259B40013 X-Rspam-User: X-HE-Tag: 1684173826-531191 X-HE-Meta: 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 BAt01LXa RZMOVu3ddPB/SZOSK/s0wmzItMVJr9knBxavtJxRElTtBxAAWldSoxo+Sf9uPdHtqF1RcPQ5ca5ht3BvM1YtyKOQZRtjJs4sncS0X9edDnk48/Cm+3UmYqszTlcb8OghR+a/WpUDYEMR/kue3ryQKFHw92DbTSGNVVu5nI2HqBlmpxqRgRdL3B8WVVjIQqk7+Rk9/BeVdGewDhjU= 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: In preparation for switching vmstat shepherd to flush per-CPU counters remotely, switch the __{mod,inc,dec} functions that modify the counters to use cmpxchg. To facilitate reviewing, functions are ordered in the text file, as: __{mod,inc,dec}_{zone,node}_page_state #ifdef CONFIG_HAVE_CMPXCHG_LOCAL {mod,inc,dec}_{zone,node}_page_state #else {mod,inc,dec}_{zone,node}_page_state #endif This patch defines the __ versions for the CONFIG_HAVE_CMPXCHG_LOCAL case to be their non-"__" counterparts: #ifdef CONFIG_HAVE_CMPXCHG_LOCAL {mod,inc,dec}_{zone,node}_page_state __{mod,inc,dec}_{zone,node}_page_state = {mod,inc,dec}_{zone,node}_page_state #else {mod,inc,dec}_{zone,node}_page_state __{mod,inc,dec}_{zone,node}_page_state #endif To test the performance difference, a page allocator microbenchmark: https://github.com/netoptimizer/prototype-kernel/blob/master/kernel/mm/bench/page_bench01.c with loops=1000000 was used, on Intel Core i7-11850H @ 2.50GHz. For the single_page_alloc_free test, which does /** Loop to measure **/ for (i = 0; i < rec->loops; i++) { my_page = alloc_page(gfp_mask); if (unlikely(my_page == NULL)) return 0; __free_page(my_page); } Unit is cycles. Vanilla Patched Diff 115.25 117 1.4% Signed-off-by: Marcelo Tosatti Index: linux-vmstat-remote/mm/vmstat.c =================================================================== --- linux-vmstat-remote.orig/mm/vmstat.c +++ linux-vmstat-remote/mm/vmstat.c @@ -334,6 +334,188 @@ void set_pgdat_percpu_threshold(pg_data_ } } +#ifdef CONFIG_HAVE_CMPXCHG_LOCAL +/* + * If we have cmpxchg_local support then we do not need to incur the overhead + * that comes with local_irq_save/restore if we use this_cpu_cmpxchg. + * + * mod_state() modifies the zone counter state through atomic per cpu + * operations. + * + * Overstep mode specifies how overstep should handled: + * 0 No overstepping + * 1 Overstepping half of threshold + * -1 Overstepping minus half of threshold + */ +static inline void mod_zone_state(struct zone *zone, enum zone_stat_item item, + long delta, int overstep_mode) +{ + struct per_cpu_zonestat __percpu *pcp = zone->per_cpu_zonestats; + s8 __percpu *p = pcp->vm_stat_diff + item; + long o, n, t, z; + + do { + z = 0; /* overflow to zone counters */ + + /* + * The fetching of the stat_threshold is racy. We may apply + * a counter threshold to the wrong the cpu if we get + * rescheduled while executing here. However, the next + * counter update will apply the threshold again and + * therefore bring the counter under the threshold again. + * + * Most of the time the thresholds are the same anyways + * for all cpus in a zone. + */ + t = this_cpu_read(pcp->stat_threshold); + + o = this_cpu_read(*p); + n = delta + o; + + if (abs(n) > t) { + int os = overstep_mode * (t >> 1); + + /* Overflow must be added to zone counters */ + z = n + os; + n = -os; + } + } while (this_cpu_cmpxchg(*p, o, n) != o); + + if (z) + zone_page_state_add(z, zone, item); +} + +void mod_zone_page_state(struct zone *zone, enum zone_stat_item item, + long delta) +{ + mod_zone_state(zone, item, delta, 0); +} +EXPORT_SYMBOL(mod_zone_page_state); + +void __mod_zone_page_state(struct zone *zone, enum zone_stat_item item, + long delta) +{ + mod_zone_state(zone, item, delta, 0); +} +EXPORT_SYMBOL(__mod_zone_page_state); + +void inc_zone_page_state(struct page *page, enum zone_stat_item item) +{ + mod_zone_state(page_zone(page), item, 1, 1); +} +EXPORT_SYMBOL(inc_zone_page_state); + +void __inc_zone_page_state(struct page *page, enum zone_stat_item item) +{ + mod_zone_state(page_zone(page), item, 1, 1); +} +EXPORT_SYMBOL(__inc_zone_page_state); + +void dec_zone_page_state(struct page *page, enum zone_stat_item item) +{ + mod_zone_state(page_zone(page), item, -1, -1); +} +EXPORT_SYMBOL(dec_zone_page_state); + +void __dec_zone_page_state(struct page *page, enum zone_stat_item item) +{ + mod_zone_state(page_zone(page), item, -1, -1); +} +EXPORT_SYMBOL(__dec_zone_page_state); + +static inline void mod_node_state(struct pglist_data *pgdat, + enum node_stat_item item, + int delta, int overstep_mode) +{ + struct per_cpu_nodestat __percpu *pcp = pgdat->per_cpu_nodestats; + s8 __percpu *p = pcp->vm_node_stat_diff + item; + long o, n, t, z; + + if (vmstat_item_in_bytes(item)) { + /* + * Only cgroups use subpage accounting right now; at + * the global level, these items still change in + * multiples of whole pages. Store them as pages + * internally to keep the per-cpu counters compact. + */ + VM_WARN_ON_ONCE(delta & (PAGE_SIZE - 1)); + delta >>= PAGE_SHIFT; + } + + do { + z = 0; /* overflow to node counters */ + + /* + * The fetching of the stat_threshold is racy. We may apply + * a counter threshold to the wrong the cpu if we get + * rescheduled while executing here. However, the next + * counter update will apply the threshold again and + * therefore bring the counter under the threshold again. + * + * Most of the time the thresholds are the same anyways + * for all cpus in a node. + */ + t = this_cpu_read(pcp->stat_threshold); + + o = this_cpu_read(*p); + n = delta + o; + + if (abs(n) > t) { + int os = overstep_mode * (t >> 1); + + /* Overflow must be added to node counters */ + z = n + os; + n = -os; + } + } while (this_cpu_cmpxchg(*p, o, n) != o); + + if (z) + node_page_state_add(z, pgdat, item); +} + +void mod_node_page_state(struct pglist_data *pgdat, enum node_stat_item item, + long delta) +{ + mod_node_state(pgdat, item, delta, 0); +} +EXPORT_SYMBOL(mod_node_page_state); + +void __mod_node_page_state(struct pglist_data *pgdat, enum node_stat_item item, + long delta) +{ + mod_node_state(pgdat, item, delta, 0); +} +EXPORT_SYMBOL(__mod_node_page_state); + +void inc_node_state(struct pglist_data *pgdat, enum node_stat_item item) +{ + mod_node_state(pgdat, item, 1, 1); +} + +void inc_node_page_state(struct page *page, enum node_stat_item item) +{ + mod_node_state(page_pgdat(page), item, 1, 1); +} +EXPORT_SYMBOL(inc_node_page_state); + +void __inc_node_page_state(struct page *page, enum node_stat_item item) +{ + mod_node_state(page_pgdat(page), item, 1, 1); +} +EXPORT_SYMBOL(__inc_node_page_state); + +void dec_node_page_state(struct page *page, enum node_stat_item item) +{ + mod_node_state(page_pgdat(page), item, -1, -1); +} +EXPORT_SYMBOL(dec_node_page_state); + +void __dec_node_page_state(struct page *page, enum node_stat_item item) +{ + mod_node_state(page_pgdat(page), item, -1, -1); +} +EXPORT_SYMBOL(__dec_node_page_state); +#else /* * For use when we know that interrupts are disabled, * or when we know that preemption is disabled and that @@ -541,149 +723,6 @@ void __dec_node_page_state(struct page * } EXPORT_SYMBOL(__dec_node_page_state); -#ifdef CONFIG_HAVE_CMPXCHG_LOCAL -/* - * If we have cmpxchg_local support then we do not need to incur the overhead - * that comes with local_irq_save/restore if we use this_cpu_cmpxchg. - * - * mod_state() modifies the zone counter state through atomic per cpu - * operations. - * - * Overstep mode specifies how overstep should handled: - * 0 No overstepping - * 1 Overstepping half of threshold - * -1 Overstepping minus half of threshold -*/ -static inline void mod_zone_state(struct zone *zone, - enum zone_stat_item item, long delta, int overstep_mode) -{ - struct per_cpu_zonestat __percpu *pcp = zone->per_cpu_zonestats; - s8 __percpu *p = pcp->vm_stat_diff + item; - long o, n, t, z; - - do { - z = 0; /* overflow to zone counters */ - - /* - * The fetching of the stat_threshold is racy. We may apply - * a counter threshold to the wrong the cpu if we get - * rescheduled while executing here. However, the next - * counter update will apply the threshold again and - * therefore bring the counter under the threshold again. - * - * Most of the time the thresholds are the same anyways - * for all cpus in a zone. - */ - t = this_cpu_read(pcp->stat_threshold); - - o = this_cpu_read(*p); - n = delta + o; - - if (abs(n) > t) { - int os = overstep_mode * (t >> 1) ; - - /* Overflow must be added to zone counters */ - z = n + os; - n = -os; - } - } while (this_cpu_cmpxchg(*p, o, n) != o); - - if (z) - zone_page_state_add(z, zone, item); -} - -void mod_zone_page_state(struct zone *zone, enum zone_stat_item item, - long delta) -{ - mod_zone_state(zone, item, delta, 0); -} -EXPORT_SYMBOL(mod_zone_page_state); - -void inc_zone_page_state(struct page *page, enum zone_stat_item item) -{ - mod_zone_state(page_zone(page), item, 1, 1); -} -EXPORT_SYMBOL(inc_zone_page_state); - -void dec_zone_page_state(struct page *page, enum zone_stat_item item) -{ - mod_zone_state(page_zone(page), item, -1, -1); -} -EXPORT_SYMBOL(dec_zone_page_state); - -static inline void mod_node_state(struct pglist_data *pgdat, - enum node_stat_item item, int delta, int overstep_mode) -{ - struct per_cpu_nodestat __percpu *pcp = pgdat->per_cpu_nodestats; - s8 __percpu *p = pcp->vm_node_stat_diff + item; - long o, n, t, z; - - if (vmstat_item_in_bytes(item)) { - /* - * Only cgroups use subpage accounting right now; at - * the global level, these items still change in - * multiples of whole pages. Store them as pages - * internally to keep the per-cpu counters compact. - */ - VM_WARN_ON_ONCE(delta & (PAGE_SIZE - 1)); - delta >>= PAGE_SHIFT; - } - - do { - z = 0; /* overflow to node counters */ - - /* - * The fetching of the stat_threshold is racy. We may apply - * a counter threshold to the wrong the cpu if we get - * rescheduled while executing here. However, the next - * counter update will apply the threshold again and - * therefore bring the counter under the threshold again. - * - * Most of the time the thresholds are the same anyways - * for all cpus in a node. - */ - t = this_cpu_read(pcp->stat_threshold); - - o = this_cpu_read(*p); - n = delta + o; - - if (abs(n) > t) { - int os = overstep_mode * (t >> 1) ; - - /* Overflow must be added to node counters */ - z = n + os; - n = -os; - } - } while (this_cpu_cmpxchg(*p, o, n) != o); - - if (z) - node_page_state_add(z, pgdat, item); -} - -void mod_node_page_state(struct pglist_data *pgdat, enum node_stat_item item, - long delta) -{ - mod_node_state(pgdat, item, delta, 0); -} -EXPORT_SYMBOL(mod_node_page_state); - -void inc_node_state(struct pglist_data *pgdat, enum node_stat_item item) -{ - mod_node_state(pgdat, item, 1, 1); -} - -void inc_node_page_state(struct page *page, enum node_stat_item item) -{ - mod_node_state(page_pgdat(page), item, 1, 1); -} -EXPORT_SYMBOL(inc_node_page_state); - -void dec_node_page_state(struct page *page, enum node_stat_item item) -{ - mod_node_state(page_pgdat(page), item, -1, -1); -} -EXPORT_SYMBOL(dec_node_page_state); -#else /* * Use interrupt disable to serialize counter updates */ Index: linux-vmstat-remote/mm/page_alloc.c =================================================================== --- linux-vmstat-remote.orig/mm/page_alloc.c +++ linux-vmstat-remote/mm/page_alloc.c @@ -6249,9 +6249,6 @@ static int page_alloc_cpu_dead(unsigned /* * Zero the differential counters of the dead processor * so that the vm statistics are consistent. - * - * This is only okay since the processor is dead and cannot - * race with what we are doing. */ cpu_vm_stats_fold(cpu);