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bh=YEKmBV4DSzD2JzeAdPDODbMxDTccaOdJer2Iy9wMS0Y=; b=x+FXYp6kZtHyLX8IdYR4raJGeqMoM+rAM5wsTMr41Uv8gz87LDfDATp8RZzOGt/59XDJfL oK5k8f+0iLnpWKZVq1K9kSiUvDm1Lgo3kgs157GmVWGnUEBXLXhtbYGQhrnBDrqH2RONcv fG6yoPIUv14I/jv4/67XfaVHBNDyw9c= X-Stat-Signature: pwpa5cuidtmfenryu1fbrykpcc6inxm9 X-Rspamd-Queue-Id: 54B9610008D X-Rspam-User: Authentication-Results: imf14.hostedemail.com; dkim=pass header.d=google.com header.s=20210112 header.b=KLtgJv7v; spf=pass (imf14.hostedemail.com: domain of shakeelb@google.com designates 209.85.216.50 as permitted sender) smtp.mailfrom=shakeelb@google.com; dmarc=pass (policy=reject) header.from=google.com X-Rspamd-Server: rspam07 X-HE-Tag: 1662743688-708143 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: On Thu, Sep 8, 2022 at 5:23 PM Michal Koutn=C3=BD wrote: > > Hello. > > On Wed, Sep 07, 2022 at 04:35:37AM +0000, Shakeel Butt wrote: > > /* Subset of vm_event_item to report for memcg event stats */ > > static const unsigned int memcg_vm_event_stat[] =3D { > > + PGPGIN, > > + PGPGOUT, > > PGSCAN_KSWAPD, > > PGSCAN_DIRECT, > > PGSTEAL_KSWAPD, > > What about adding a dummy entry at the beginning like: > > static const unsigned int memcg_vm_event_stat[] =3D { > + NR_VM_EVENT_ITEMS, > + PGPGIN, > + PGPGOUT, > PGSCAN_KSWAPD, > PGSCAN_DIRECT, > > > > @@ -692,14 +694,30 @@ static const unsigned int memcg_vm_event_stat[] = =3D { > > #endif > > }; > > > > +#define NR_MEMCG_EVENTS ARRAY_SIZE(memcg_vm_event_stat) > > +static int mem_cgroup_events_index[NR_VM_EVENT_ITEMS] __read_mostly; > > + > > +static void init_memcg_events(void) > > +{ > > + int i; > > + > > + for (i =3D 0; i < NR_MEMCG_EVENTS; ++i) > > + mem_cgroup_events_index[memcg_vm_event_stat[i]] =3D i + 1= ; > > Start such loops from i =3D 1, save i to the table. > > > +} > > + > > +static inline int memcg_events_index(enum vm_event_item idx) > > +{ > > + return mem_cgroup_events_index[idx] - 1; > > +} > > And the there'd be no need for the reverse transforms -1. > > I.e. it might be just a negligible micro-optimization but since the > event updates are on some fast (albeit longer) paths, it may be worth > sacrificing one of the saved 8Bs in favor of no arithmetics. > > What do you think about this? > > > static unsigned long memcg_events(struct mem_cgroup *memcg, int event) > > { > > - return READ_ONCE(memcg->vmstats->events[event]); > > + int index =3D memcg_events_index(event); > > + > > + if (index < 0) > > + return 0; > > As a bonus these undefined maps could use the zero at the dummy location > without branch (slow paths though). > > > > @@ -5477,7 +5511,7 @@ static void mem_cgroup_css_rstat_flush(struct cgr= oup_subsys_state *css, int cpu) > > parent->vmstats->state_pending[i] +=3D delta; > > } > > > > - for (i =3D 0; i < NR_VM_EVENT_ITEMS; i++) { > > + for (i =3D 0; i < NR_MEMCG_EVENTS; i++) { > > I applaud this part :-) > > Hi Michal, Thanks for taking a look. Let me get back to you on this later. I am at the moment rearranging struct mem_cgroup for better packing and will be running some benchmarks. Later I will see if your suggestion has any performance benefit or just more readable code then I will follow up. Shakeel