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[96.255.20.42]) by smtp.gmail.com with ESMTPSA id af79cd13be357-7cd468cb64asm963413385a.99.2025.05.21.20.24.28 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 21 May 2025 20:24:29 -0700 (PDT) Date: Wed, 21 May 2025 23:24:27 -0400 From: Gregory Price To: Zi Yan Cc: Bharata B Rao , Donet Tom , linux-kernel@vger.kernel.org, linux-mm@kvack.org, Jonathan.Cameron@huawei.com, dave.hansen@intel.com, hannes@cmpxchg.org, mgorman@techsingularity.net, mingo@redhat.com, peterz@infradead.org, raghavendra.kt@amd.com, riel@surriel.com, rientjes@google.com, sj@kernel.org, weixugc@google.com, willy@infradead.org, ying.huang@linux.alibaba.com, dave@stgolabs.net, nifan.cxl@gmail.com, joshua.hahnjy@gmail.com, xuezhengchu@huawei.com, yiannis@zptcorp.com, akpm@linux-foundation.org, david@redhat.com Subject: Re: [RFC PATCH v0 2/2] mm: sched: Batch-migrate misplaced pages Message-ID: References: <20250521080238.209678-1-bharata@amd.com> <20250521080238.209678-3-bharata@amd.com> <6795B38D-7858-4ADE-BB3B-71A1950A284D@nvidia.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <6795B38D-7858-4ADE-BB3B-71A1950A284D@nvidia.com> X-Rspamd-Queue-Id: 036CA180006 X-Stat-Signature: wz356e8u6ihhcxff4ozst8zm1kjf8fha X-Rspam-User: X-Rspamd-Server: rspam04 X-HE-Tag: 1747884270-809604 X-HE-Meta: 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 bKA9E+E+ +bKuZ/6mr7X6qhi/30q9o94R7S7MDZq3hlxilMON7fW4IZnhuhYBkrf2yY7O6LUounuPjGSEiZbjS6bJJhoycMKZ5VeZERC8LwPYSlfdnZ3L3Bysvxg0UqzAapNGSoe+T4lLyyMY6ffysBFWQ2kXECRwCZN5n0sDD9hZx59nZVxftVkaM3e2NB7fz699FY0ztl+k7RwPecXWcWZsHUq8LmPb3f96rffKvW33cd8holOqwmPIGH49TpL1zzywlicbbDqZ7Mkt5EHV5mCQbOUtkAiff8dIGGnIeu4UqkA8S4rZwFn9cDAuwhRkn9ETISnqloeqZkCNmu3UAXzCnkr7NT/cNxS1b/5lLZpsN7BbC4//iWJFqLYICmTCBHe224C9SKMNvIBjvWKSTa1KVPmRrf0fGxw== 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: On Wed, May 21, 2025 at 02:40:53PM -0400, Zi Yan wrote: > On 21 May 2025, at 14:25, Donet Tom wrote: > > Hi Bharatha, > > > > This is target node ID right? > > In memory tiering mode, folio_last_cpupid() gives page access time > for slow memory folios. In !folio_use_access_time() case, > folio_last_cpupid() gives last cpupid. Now it is reused for node > id. It is too confusing. At least, a new function like folio_get_target_nid() > should be added to return a nid only if folio is isolated. > The really annoying part of all of this is #ifdef CONFIG_NUMA_BALANCING #ifdef LAST_CPUPID_NOT_IN_PAGE_FLAGS static inline int folio_last_cpupid(struct folio *folio) { return folio->_last_cpupid; } #else static inline int folio_last_cpupid(struct folio *folio) { return (folio->flags >> LAST_CPUPID_PGSHIFT) & LAST_CPUPID_MASK; } #endif #else /* !CONFIG_NUMA_BALANCING */ static inline int folio_last_cpupid(struct folio *folio) { return folio_nid(folio); /* XXX */ } ... #endif Obviously we don't have to care about the !NUMAB case, but what a silly muxing we have going on here (I get it, space is tight - the interfaces are just confusing is all). My question is whether there's some kind of race condition here if the mode changes between isolate and fetch. Can we "fetch a node id" and end up with a cpupid because someone toggled the between tiering and balancing? If we can answer that, then implementing folio_last_cpupid and folio_last_access_nid can return -1 if called in the wrong mode (assuming this check isn't too expensive). That would be a nice cleanup for readability sake. ~Gregory