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smtp.subspace.kernel.org; dkim=pass header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=f1Y6buIo; arc=none smtp.remote-ip=100.103.45.18 Received: from smtp.kernel.org (quasi.space.kernel.org [100.103.45.18]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 707BA606A31A; Thu, 29 Oct 2026 18:08:07 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=k20260515 header.b=f1Y6buIo Received: by smtp.kernel.org (Postfix) with ESMTPSA id 02EF91F01816; Thu, 29 Oct 2026 18:08:02 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793297287; bh=Dzqh+wdXVDD6rZ18+/BTNNGOJs3aTGYsg31/1TNDADw=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=f1Y6buIomjd8NiYiwC6+L/N/2gFzxBK/PTis/OryQtGQXon5fydlVHG395evTsZmx N4jboM2OkA3ya5OrYrllwnpe+kG+jOmUDYRXK+DGcBEX2/nOkOV31x/bMvQpJnopvG 7Z2lG945Ov3nX576VROmqMDKZlqUQsOyo/B/ZYq9LrxDRAW/aKhZxuW9lFRx9c45px Jwf5vHxk0COCrcMoKMqnZT6qZ/tzhUODUrW0/2m7r3BcT5voMK8LY5N4HrDYwvdg71 kjfdi6qj4h8ApblSoT1kLHdK8Ti//IC5Ulk/kEtn5KhYMcS0OaoA3PtDBj0a38iVEH buw6b2not2y5Q== Message-ID: Date: Thu, 29 Oct 2026 19:08:01 +0100 X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v4 6/8] mm/hugetlb: retry the pool walk when the zonelist is rebuilt Content-Language: en-US To: "Gregory Price (Meta)" , linux-mm@kvack.org Cc: linux-kernel@vger.kernel.org, kernel-team@meta.com, muchun.song@linux.dev, osalvador@suse.de, david@kernel.org, akpm@linux-foundation.org, ziy@nvidia.com, joshua.hahnjy@gmail.com, rakie.kim@sk.com, ying.huang@linux.alibaba.com, ljs@kernel.org, liam@infradead.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com, brendan.jackman@linux.dev, hannes@cmpxchg.org, mgorman@techsingularity.net, anshuman.khandual@arm.com, stable@vger.kernel.org References: <20261028211930.3504634-1-gourry@gourry.net> <20261028211930.3504634-7-gourry@gourry.net> From: "Vlastimil Babka (SUSE)" Autocrypt: addr=vbabka@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 10/28/26 22:19, Gregory Price (Meta) wrote: > Onlining the first block of a zone rebuilds every zonelist in place, > shifting the slots after the new zone. dequeue_hugetlb_folio_nodemask() > approves a slot by its node, then loads the zone from it, so a hugetlb > fault bound to one node can take a pool page from another: > > CPU 0 CPU 1 > dequeue_hugetlb_folio_nodemask(nodemask {2}) > slot 3 (NORMAL2) approved > online_pages() > build_all_zonelists() > [.., NORMAL1, NORMAL2] > -> [.., MOVABLE1, NORMAL1, ...] > zone = zonelist_zone(slot 3) /* NORMAL1 */ > dequeue_hugetlb_folio_node_exact(h, 1) > > Check zonelist_update_seq before using each zone, and on the way out > with nothing found, and restart the walk if it changed. Checking before > the dequeue leaves nothing to put back. Reset the last-tried node on > restart, so it is not skipped. > > With kprobes holding the walk across the online, a fault bound to node 2 > took a node 1 page in 3 of 3 runs, and a node 2 page in 3 of 3 with this > change. > > Fixes: 11cd8638c37f ("mm, page_alloc: remove stop_machine from build_all_zonelists") > Cc: stable@vger.kernel.org > Signed-off-by: Gregory Price (Meta) LGTM, but... > --- > mm/hugetlb.c | 13 ++++++++++--- > mm/page_alloc.c | 4 ++-- > mm/page_alloc.h | 3 +++ > 3 files changed, 15 insertions(+), 5 deletions(-) > > diff --git a/mm/hugetlb.c b/mm/hugetlb.c > index b37d7d0db7fc..8edf323baf0f 100644 > --- a/mm/hugetlb.c > +++ b/mm/hugetlb.c > @@ -1293,11 +1293,11 @@ static struct folio *dequeue_hugetlb_folio_node_exact(struct hstate *h, > static struct folio *dequeue_hugetlb_folio_nodemask(struct hstate *h, gfp_t gfp_mask, > int nid, nodemask_t *nmask) > { > - unsigned int cpuset_mems_cookie; > + unsigned int cpuset_mems_cookie, zonelist_cookie; > struct zonelist *zonelist; > struct zone *zone; > struct zoneref *z; > - int node = NUMA_NO_NODE; > + int node; > > /* 'nid' should not be NUMA_NO_NODE. Try to catch any misuse of it and rectifiy. */ > if (nid == NUMA_NO_NODE) > @@ -1306,10 +1306,16 @@ static struct folio *dequeue_hugetlb_folio_nodemask(struct hstate *h, gfp_t gfp_ > zonelist = node_zonelist(nid, gfp_mask); > > retry_cpuset: > + node = NUMA_NO_NODE; > cpuset_mems_cookie = read_mems_allowed_begin(); > + zonelist_cookie = zonelist_iter_begin(); > for_each_zone_zonelist_nodemask(zone, z, zonelist, gfp_zone(gfp_mask), nmask) { > struct folio *folio; > > + /* A rebuild may have shifted a node outside @nmask into this slot. */ > + if (unlikely(check_retry_zonelist(zonelist_cookie))) > + goto retry_cpuset; > + > if (!cpuset_zone_allowed(zone, gfp_mask)) > continue; > /* > @@ -1324,7 +1330,8 @@ static struct folio *dequeue_hugetlb_folio_nodemask(struct hstate *h, gfp_t gfp_ > if (folio) > return folio; > } > - if (unlikely(read_mems_allowed_retry(cpuset_mems_cookie))) > + if (unlikely(read_mems_allowed_retry(cpuset_mems_cookie) || > + check_retry_zonelist(zonelist_cookie))) > goto retry_cpuset; > > return NULL; > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index 33aab9deaaa1..70830689048a 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -4411,7 +4411,7 @@ EXPORT_SYMBOL_GPL(fs_reclaim_release); > */ > static DEFINE_SEQLOCK(zonelist_update_seq); > > -static unsigned int zonelist_iter_begin(void) > +unsigned int zonelist_iter_begin(void) > { > if (IS_ENABLED(CONFIG_MEMORY_HOTPLUG)) > return read_seqbegin(&zonelist_update_seq); > @@ -4432,7 +4432,7 @@ static unsigned int zonelist_iter_sample(void) > return 0; > } > > -static unsigned int check_retry_zonelist(unsigned int seq) > +unsigned int check_retry_zonelist(unsigned int seq) > { > if (IS_ENABLED(CONFIG_MEMORY_HOTPLUG)) > return read_seqretry(&zonelist_update_seq, seq); > diff --git a/mm/page_alloc.h b/mm/page_alloc.h > index 2b1017a91928..53df6b8a0c00 100644 > --- a/mm/page_alloc.h > +++ b/mm/page_alloc.h > @@ -265,6 +265,9 @@ extern void zone_pcp_disable(struct zone *zone); > extern void zone_pcp_enable(struct zone *zone); > extern void zone_pcp_init(struct zone *zone); > > +unsigned int zonelist_iter_begin(void); > +unsigned int check_retry_zonelist(unsigned int seq); ... is it possible to inline these here instead? > + > enum fallback_result { > /* Found suitable migratetype, *mt_out is valid. */ > FALLBACK_FOUND,