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[173.79.60.52]) by smtp.gmail.com with ESMTPSA id af79cd13be357-93bedaf3e7bsm43010485a.30.2026.09.18.14.49.38 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 18 Sep 2026 14:49:39 -0700 (PDT) Date: Fri, 18 Sep 2026 17:49:37 -0400 From: Gregory Price To: "David Hildenbrand (Arm)" Cc: linux-mm@kvack.org, linux-kernel@vger.kernel.org, kernel-team@meta.com, akpm@linux-foundation.org, ljs@kernel.org, liam@infradead.org, vbabka@kernel.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com, brendan.jackman@linux.dev, hannes@cmpxchg.org, ziy@nvidia.com, Balbir Singh Subject: Re: [PATCH v2 1/2] mm: refactor find_next_best_node to find_next_best_node_in Message-ID: References: <20260912030424.2889731-1-gourry@gourry.net> <20260912030424.2889731-2-gourry@gourry.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: B067B40006 X-Rspam-User: X-Stat-Signature: dq455435xgu8f4ibwkh1hwred5mcxqp9 X-HE-Tag: 1789768180-797359 X-HE-Meta: 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 sx5vwGdS jfKUKROFgxoyuCv35zpwjto+T0zWfRccTKbVlNtPRy6rDvx4XpmWcxEmRMX2E8M8Ki+JRgMH96dW9185JvtmcTK/FFuRmRJ6sig3LCsdrA/Py51HNbmbk5jWX8DvOkrrxD3eTXutZEARo9u6cJz1a7S3E2OmAI9iqyUOMFATMd6vY+71nu/iAQO9m3Np/w7nwawBAZ4Fc2C+XP6roOGBTzlF77bw69xichv3WfV52+5EW5ium1PcorEDQwHbCM0mEHJAZ3wKp+wKjrLu2cFeVAXsvew3p3bX5svN59yjQurcwhkqRm3EqjT7e3/1zj8/9C175i50XtWhjCkDAxVrcFGVPkKcHXseqZTNbivkaNNHqxrTcsvZ7fWPx3w== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, Sep 18, 2026 at 10:42:12PM +0200, David Hildenbrand (Arm) wrote: > > diff --git a/mm/internal.h b/mm/internal.h > > index da14c56fb24e..1519dd21a900 100644 > > --- a/mm/internal.h > > +++ b/mm/internal.h > > @@ -1133,7 +1133,8 @@ extern int node_reclaim_mode; > > > > extern unsigned long node_reclaim(struct pglist_data *pgdat, > > gfp_t gfp_mask, unsigned int order); > > -extern int find_next_best_node(int node, nodemask_t *used_node_mask); > > +int find_next_best_node_in(int node, nodemask_t *used_node_mask, > > + const nodemask_t *candidates); > > Just curious, for your use case, wouldn't it be enough to pass N_MEMORY? > > Or do we expect to pass other actual node masks that are not derived from > node_states? > That is the base case today - and in fact that's what's hard-coded in the current logic. For the private node series we will pass: ZONELIST_FALLBACK: N_MEMORY_GENERAL /* general purpose nodes */ ZONELIST_PRIVATE: N_MEMORY /* All nodes, including private */ ZONELIST_KTEST: (N_MEMORY_GENERAL ^ N_MEMORY) /* private only */ the ZONELIST_KTEST is something i'm still working with - but it gives us fully isolated pgdat structures that allow a KTEST to treat the node mutations as determinstic and otherwise unreachable by the kernel (because the kernel outside ktest can't select ZOENLIST_KTEST). ANYWAY... I don't expect us to build hundreds of these zonelists - they are expensive to construct (space-wise), but that's largely because we haven't needed to optimize it. But you could imagine having a custom zonelist built on a subset of N_MEMORY so that you could do like... for_each_reclaimable_zone(z) { /* Reclaim */ } and hide all this nasty zone business from other components of mm/ that really don't need all that complexity (at most they want the LRUs). ~Gregory