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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=VtievZEi; 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 B3CEF60A380E; Thu, 29 Oct 2026 18:10:25 +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=VtievZEi Received: by smtp.kernel.org (Postfix) with ESMTPSA id 565281F01176; Thu, 29 Oct 2026 18:10:21 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1793297425; bh=YhtoC8abtd12mu+rBuvcv/XkTwddyXJZrrtv2/voX0Y=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=VtievZEidSVJKJ8wgbiTyLqG2cFPhE5Pkzw8ITYYjhGHuopw91uKJ9JtJJdRSMp7F M2UqZkhfBFg1lLeA8FWkN2BhW/bw5tRWjEgKb5mCzZHqQhOKiRyb5dBXGRNKduN/C/ HdJX54ceYFkIb/lIpcSEH7JL9BNLd2+wXtYeqxBfrzz35lBQkZFDs2sMw+rNalIzlZ H/Yz0Rg0YFmSD1A+4EfXPNMfRbhHRh9eLrQyrr6++JrV5sREhUgg9l3wqbVMCRXPBU 116/V5xj5GH0fxIc/woLjEPZOKHPaBaWmzSg1SSYfwsx5cyHxvemiTdvhRWAnXNXkI z1GGNTHz/rJGg== Message-ID: <7a1807d0-4f3b-4094-b73b-b6950040e3ab@kernel.org> Date: Thu, 29 Oct 2026 19:10:19 +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 7/8] mm/page_alloc: retry alloc_contig_pages() 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> <20261028211930.3504634-8-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. > alloc_contig_frozen_pages_noprof() approves a slot by the caller's gfp > and nodemask, then loads the zone from it: > > CPU 0 CPU 1 > alloc_contig_frozen_pages_noprof(GFP_HIGHUSER | __GFP_THISNODE) > slot 0 (NORMAL1) approved > online_pages() > build_all_zonelists() > [NORMAL1] > -> [MOVABLE1, NORMAL1] > zone = zonelist_zone(slot 0) /* MOVABLE1 */ > alloc_contig_frozen_range(MOVABLE1 pfns) > > A gigantic hugetlb page can then land in ZONE_MOVABLE, and a nodemask > caller can get a range from another node. Gigantic pages are kept out > of ZONE_MOVABLE since commit 79b63f12abcb ("mm, hugetlb: do not allocate > non-migrateable gigantic pages from movable zones"). > > Check zonelist_update_seq before using each zone, and restart the walk > if it changed, as the hugetlb pool walk does. Check again before > escalating to the pass that may migrate hugetlb pages, so a pass a > rebuild cut short is redone rather than escalated. > > With kprobes holding the walk across the online, the base kernel put the > 1G page in ZONE_MOVABLE in 3 of 3 runs, and this change put it in > ZONE_NORMAL in 3 of 3. Direct GFP_KERNEL calls with nodemask {1} and > {2} got a ZONE_MOVABLE range and a node 1 range on base, 3 of 3 each, > and neither with this change. > > Fixes: 5e27a2df03b8 ("mm/page_alloc: add alloc_contig_pages()") > Cc: stable@vger.kernel.org > Signed-off-by: Gregory Price (Meta) Reviewed-by: Vlastimil Babka (SUSE) > --- > mm/page_alloc.c | 9 +++++++++ > 1 file changed, 9 insertions(+) > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index 70830689048a..7d06c6c4011a 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -7593,6 +7593,7 @@ struct page *alloc_contig_frozen_pages_noprof(unsigned long nr_pages, > gfp_t gfp_mask, int nid, nodemask_t *nodemask) > { > unsigned long ret, pfn, flags; > + unsigned int zonelist_cookie; > struct zonelist *zonelist; > struct zone *zone; > struct zoneref *z; > @@ -7601,8 +7602,13 @@ struct page *alloc_contig_frozen_pages_noprof(unsigned long nr_pages, > > retry: > zonelist = node_zonelist(nid, gfp_mask); > + zonelist_cookie = zonelist_iter_begin(); > for_each_zone_zonelist_nodemask(zone, z, zonelist, > gfp_zone(gfp_mask), nodemask) { > + /* A rebuild may have shifted an ineligible zone into this slot. */ > + if (unlikely(check_retry_zonelist(zonelist_cookie))) > + goto retry; > + > spin_lock_irqsave(&zone->lock, flags); > > pfn = ALIGN(zone->zone_start_pfn, nr_pages); > @@ -7637,6 +7643,9 @@ struct page *alloc_contig_frozen_pages_noprof(unsigned long nr_pages, > * second pass, we will try moving HugeTLB pages when those pages are > * smaller than the requested contiguous region size. > */ > + /* Redo a pass that a rebuild cut short before escalating. */ > + if (unlikely(check_retry_zonelist(zonelist_cookie))) > + goto retry; > if (skip_hugetlb && skipped_hugetlb) { > skip_hugetlb = false; > goto retry;