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[173.79.60.52]) by smtp.gmail.com with ESMTPSA id d75a77b69052e-530331dc460sm31323441cf.18.2026.09.02.17.52.40 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 02 Sep 2026 17:52:41 -0700 (PDT) Date: Wed, 2 Sep 2026 20:52:39 -0400 From: Gregory Price To: linux-mm@kvack.org Cc: linux-cxl@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-team@meta.com, david@kernel.org, osalvador@suse.de, akpm@linux-foundation.org Subject: Re: [PATCH] mm/memory_hotplug: factor out node_is_memoryless() Message-ID: References: <20260902195507.88655-1-gourry@gourry.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260902195507.88655-1-gourry@gourry.net> X-Stat-Signature: jjj8gycmwqu9zboo3i5inr1deqdk1x9u X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: BBA20160002 X-Rspam-User: X-HE-Tag: 1788396762-504278 X-HE-Meta: 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 KaHi/QxW 2pOsb874PqiA1TNXWaSqET6UX8sTr1ZzSKFlyJTti1omcyyw9brXZkgzIapodDUWeRLc02J1xaNh75HxDbAY16qGlafjxaI9ARSGYQvFS8dg2ESyz9JRHabglRhKRyKp/mybZ5TFgK4OKgIHUYItkqVJF1B9skaeNRObUuvAXBwPgAWb/RGXj4+mAAbq50vKf9nBiUxOyxZ3Atmgw2nAl6Ia44yD4Zs721YpW/4M7hBoZ61aPZvciah47z18eoUL20ERMvstiFSVV5fICPhMU/U8kpfK1+V574NS9PM/CQTz9j8bp5l2G0a/x4EAXQYlYyVpWdedldsXE03uxmPS3PxM0RmgmbCe+CDSH2gXoHvXiFWonbBrpwxYJvY5ZQ9+FVnx1CYugoYjTlWHVD1lT8QBxGdx2pRuE0HoeBj9HXYBBr5bKZs9Z0tOR/A== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, Sep 02, 2026 at 03:55:07PM -0400, Gregory Price wrote: > A memoryless node neither spans present pages (populated or ZONE_DEVICE) > nor has an offline-but-added memory block still linked to it in sysfs. > > try_offline_node() presently open-codes this memoryless check. > > Pull that into a node_is_memoryless() helper and pull the existing > check_no_memblock_for_node_cb() helper ahead of the add/online path > so it's clearer what is happening here. > > No functional change. > > Signed-off-by: Gregory Price > --- > mm/memory_hotplug.c | 60 +++++++++++++++++++++++---------------------- > 1 file changed, 31 insertions(+), 29 deletions(-) > > diff --git a/mm/memory_hotplug.c b/mm/memory_hotplug.c > index 226ab9cb078ad..d0e94057682af 100644 > --- a/mm/memory_hotplug.c > +++ b/mm/memory_hotplug.c > @@ -1491,6 +1491,36 @@ static int create_altmaps_and_memory_blocks(int nid, struct memory_group *group, > return ret; > } > > +static int check_no_memblock_for_node_cb(struct memory_block *mem, void *arg) > +{ > + int nid = *(int *)arg; > + > + /* > + * If a memory block belongs to multiple nodes, the stored nid is not > + * reliable. However, such blocks are always online (e.g., cannot get > + * offlined) and, therefore, are still spanned by the node. > + */ > + return mem->nid == nid ? -EEXIST : 0; > +} > + > +/* Caller must hold the memory hotplug lock for this check. */ > +static bool node_is_memoryless(int nid) > +{ > + /* > + * A node still spanning pages (especially ZONE_DEVICE) is not > + * memoryless. A node spans memory after move_pfn_range_to_zone(), > + * e.g. once a memory block has been onlined. > + */ > + if (node_spanned_pages(nid)) > + return false; browsing sashiko feedback: [Severity: High] This is a pre-existing issue and was not introduced by this patch, but can this lockless read of node_spanned_pages() race with ZONE_DEVICE memory hotplug? --- This seems legit and worth addressing (other notes are addressible as well, but this is maybe noteworthy). I actually have some old patches sandbagged that tried to marry the ZONE_DEVICE hotplug pattern through mm/memory_hotplug.c rather than its separare entry-point. Might be worth a revisit. I don't know that I want to predicate this particular fix on this patch but it's worth a think. ~Gregory