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[173.79.56.208]) by smtp.gmail.com with ESMTPSA id af79cd13be357-7c573da47ddsm593190685a.117.2025.03.17.08.05.10 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 17 Mar 2025 08:05:11 -0700 (PDT) Date: Mon, 17 Mar 2025 11:05:08 -0400 From: Gregory Price To: Bharata B Rao Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, AneeshKumar.KizhakeVeetil@arm.com, Hasan.Maruf@amd.com, Jonathan.Cameron@huawei.com, Michael.Day@amd.com, akpm@linux-foundation.org, dave.hansen@intel.com, david@redhat.com, feng.tang@intel.com, hannes@cmpxchg.org, honggyu.kim@sk.com, hughd@google.com, jhubbard@nvidia.com, k.shutemov@gmail.com, kbusch@meta.com, kmanaouil.dev@gmail.com, leesuyeon0506@gmail.com, leillc@google.com, liam.howlett@oracle.com, mgorman@techsingularity.net, mingo@redhat.com, nadav.amit@gmail.com, nphamcs@gmail.com, peterz@infradead.org, raghavendra.kt@amd.com, riel@surriel.com, rientjes@google.com, rppt@kernel.org, shivankg@amd.com, shy828301@gmail.com, sj@kernel.org, vbabka@suse.cz, weixugc@google.com, willy@infradead.org, ying.huang@linux.alibaba.com, ziy@nvidia.com, yuanchu@google.com Subject: Re: [RFC PATCH 2/4] mm: kpromoted: Hot page info collection and promotion daemon Message-ID: References: <20250306054532.221138-1-bharata@amd.com> <20250306054532.221138-3-bharata@amd.com> <20250313164430.bzkfyqmx6a5dj7d2@offworld> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: On Mon, Mar 17, 2025 at 09:09:18AM +0530, Bharata B Rao wrote: > On 13-Mar-25 10:14 PM, Davidlohr Bueso wrote: > > On Thu, 06 Mar 2025, Bharata B Rao wrote: > > > > > +static int page_should_be_promoted(struct page_hotness_info *phi) > > > +{ > > > +    struct page *page = pfn_to_online_page(phi->pfn); > > > +    unsigned long now = jiffies; > > > +    struct folio *folio; > > > + > > > +    if (!page || is_zone_device_page(page)) > > > +        return false; > > > + > > > +    folio = page_folio(page); > > > +    if (!folio_test_lru(folio)) { > > > +        count_vm_event(KPROMOTED_MIG_NON_LRU); > > > +        return false; > > > +    } > > > +    if (folio_nid(folio) == phi->hot_node) { > > > +        count_vm_event(KPROMOTED_MIG_RIGHT_NODE); > > > +        return false; > > > +    } > > > > How about using the LRU age itself: > > Sounds like a good check for page hotness. > > > > > if (folio_test_active()) > >    return true; > > But the numbers I obtained with this check added, didn't really hit this > condition all that much. I was running a multi-threaded application that > allocates enough memory such that the allocation spills over from DRAM node > to the CXL node. Threads keep touching the memory pages in random order. > Is demotion enabled by any chance? i.e. are you sure it's actually allocating from CXL and not demoting cold stuff to CXL? > kpromoted_recorded_accesses 960620 /* Number of recorded accesses */ > kpromoted_recorded_hwhints 960620 /* Nr accesses via HW hints, IBS in this > case */ > kpromoted_recorded_pgtscans 0 > kpromoted_record_toptier 638006 /* Nr toptier accesses */ > kpromoted_record_added 321234 /* Nr (CXL) accesses that are tracked */ > kpromoted_record_exists 1380 > kpromoted_mig_right_node 0 > kpromoted_mig_non_lru 226 > kpromoted_mig_lru_active 47 /* Number of accesses considered for promotion > as determined by folio_test_active() check */ > kpromoted_mig_cold_old 0 > kpromoted_mig_cold_not_accessed 1373 > kpromoted_mig_candidate 319635 > kpromoted_mig_promoted 319635 > kpromoted_mig_dropped 1599 > > Need to check why is this the case. > > > > > > + > > > +    /* If the page was hot a while ago, don't promote */ > > > +    if ((now - phi->last_update) > 2 * > > > msecs_to_jiffies(KPROMOTED_FREQ_WINDOW)) { > > > +        count_vm_event(KPROMOTED_MIG_COLD_OLD); > > > +        return false; > > > +    } > > > + > > > +    /* If the page hasn't been accessed enough number of times, > > > don't promote */ > > > +    if (phi->frequency < KPRMOTED_FREQ_THRESHOLD) { > > > +        count_vm_event(KPROMOTED_MIG_COLD_NOT_ACCESSED); > > > +        return false; > > > +    } > > > +    return true; > > > +} > > > > ... > > > > > +static int kpromoted(void *p) > > > +{ > > > +    pg_data_t *pgdat = (pg_data_t *)p; > > > +    struct task_struct *tsk = current; > > > +    long timeout = msecs_to_jiffies(KPROMOTE_DELAY); > > > + > > > +    const struct cpumask *cpumask = cpumask_of_node(pgdat->node_id); > > > + > > > +    if (!cpumask_empty(cpumask)) > > > +        set_cpus_allowed_ptr(tsk, cpumask); > > > > Explicit cpumasks are not needed if you use kthread_create_on_node(). > > Thanks, will incorporate. > > Regards, > Bharata.