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imf09.hostedemail.com; dkim=pass header.d=kernel.org header.s=k20201202 header.b=Fz1J6g5F; spf=pass (imf09.hostedemail.com: domain of david@kernel.org designates 172.105.4.254 as permitted sender) smtp.mailfrom=david@kernel.org; dmarc=pass (policy=quarantine) header.from=kernel.org ARC-Seal: i=1; s=arc-20220608; d=hostedemail.com; t=1773303971; a=rsa-sha256; cv=none; b=Cc/aOZgH4jOUErWUg82B7NhishFGRUzO0A1wS6+FFw8TT3Xg62KXW3gzyrBnLxi9ylFEPp kgQFnZzovT2ugT8cCTAKMJkiuhYSv2y5IjUY6ZwaSwENpQkuOzoa7QCkFEO0TnqfP+ThcR 1NLia02YFbDTcdTxW9WaW6GOQHNraik= Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by tor.source.kernel.org (Postfix) with ESMTP id C125660054; Thu, 12 Mar 2026 08:26:10 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 7F604C4CEF7; Thu, 12 Mar 2026 08:26:06 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1773303970; bh=xZibF95cdQn3VPiOBxZvA/wo6LUPkv6y1GlNkUEs+zU=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=Fz1J6g5FPq2kdTVJCyroElAsGH7tIdNBJr0gOKHUlXb0iJ9D8w5fL7bZV9y/uYEuL 3/7qg+iqqHDUw7GOdA5OdT5KIc8eU9hoh7LOn4zBnk97CMLc88h/G0FwOEjgdt9g9I ynZncZLJfn26q8akPOsJoQHZdybS07NAgZQixItiPxRjU5vd4QeiUfrpuobydiZoPJ AtKDcBNXJ/0njtH6AINL9p3iuj/ZnCgpNRKj7KMibVqJYRPn2C6H/aTXaNZinSU9jI EN/ZhgdqDG4lggg7AdNjTwQC7dZ7hyopY3y96T5vI8lwQBmHStPAJPCh0sFp3FkB64 PXkvpp9a+wznw== Message-ID: <42273acc-7ad2-4832-a154-20fd49a460d0@kernel.org> Date: Thu, 12 Mar 2026 09:26:04 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2] mm: migrate: requeue destination folio on deferred split queue To: Wei Yang , Usama Arif Cc: Andrew Morton , npache@redhat.com, ziy@nvidia.com, willy@infradead.org, linux-mm@kvack.org, matthew.brost@intel.com, joshua.hahnjy@gmail.com, hannes@cmpxchg.org, rakie.kim@sk.com, byungchul@sk.com, gourry@gourry.net, ying.huang@linux.alibaba.com, apopple@nvidia.com, linux-kernel@vger.kernel.org, kernel-team@meta.com References: <20260310105419.3256755-1-usama.arif@linux.dev> <20260312031831.xb6rvrelhw54cmio@master> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspam-User: X-Rspamd-Queue-Id: 6F7E2140006 X-Rspamd-Server: rspam08 X-Stat-Signature: beu7tce5o3w615xaych7x3wdmmexpet3 X-HE-Tag: 1773303971-13062 X-HE-Meta: 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 2qlxzvTv 9/IS00lG4sQoarYKZrVhSpK0/PK+AwpVDFtDeEYTxgESJ/cGHwuN/LwwuLOu6u9FL84VQ0j5A+eIZNNck5w7tAzVslAtYIB7UK+v2A8E3ONnQNzQQRxCuE+xvm4f9v6s55rDe/qRiNjPU9Ozs4EMj0m7xWPcoTp+jvEV4CjQh9UZO+Jl6n9qG8tRlkN/0EFPcX8DUCNhLHlTB64glk9hM/4SaToReKN7QW/nG1fvFbcBOKUVcfPJOY+21npXphdLhk0Nbx29Nj0KeFjJesCuIn5lzMNdrNoBNVi2njQp9gPym8YOW0vN+23dbQCTysCQBAZnpj7G8Y3o5JiqzJ0jRFujep2iS7qE80GGOxyUnVcH0pr/WtdgtlQ2mw4T11l1hu5gP Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 3/12/26 04:18, Wei Yang wrote: > On Tue, Mar 10, 2026 at 03:54:19AM -0700, Usama Arif wrote: >> During folio migration, __folio_migrate_mapping() removes the source >> folio from the deferred split queue, but the destination folio is never >> re-queued. This causes underutilized THPs to escape the shrinker after >> NUMA migration, since they silently drop off the deferred split list. >> >> Fix this by recording whether the source folio was on the deferred split >> queue and its partially mapped state before move_to_new_folio() unqueues >> it, and re-queuing the destination folio after a successful migration if >> it was. >> >> By the time migrate_folio_move() runs, partially mapped folios without a >> pin have already been split by migrate_pages_batch(). So only two cases >> remain on the deferred list at this point: >> 1. Partially mapped folios with a pin (split failed). >> 2. Fully mapped but potentially underused folios. >> The recorded partially_mapped state is forwarded to deferred_split_folio() >> so that the destination folio is correctly re-queued in both cases. >> >> Reported-by: Johannes Weiner >> Fixes: dafff3f4c850 ("mm: split underused THPs") >> Signed-off-by: Usama Arif >> --- >> v1 -> v2: >> - record whether source folio was on the deferred split queue before >> move_to_folio() (David) >> - record partially mapped state and update commit message (Zi) >> --- >> mm/migrate.c | 17 +++++++++++++++++ >> 1 file changed, 17 insertions(+) >> >> diff --git a/mm/migrate.c b/mm/migrate.c >> index ece77ccb2ec0..61013d258eb4 100644 >> --- a/mm/migrate.c >> +++ b/mm/migrate.c >> @@ -1360,6 +1360,8 @@ static int migrate_folio_move(free_folio_t put_new_folio, unsigned long private, >> int rc; >> int old_page_state = 0; >> struct anon_vma *anon_vma = NULL; >> + bool src_deferred_split = false; >> + bool src_partially_mapped = false; >> struct list_head *prev; >> >> __migrate_folio_extract(dst, &old_page_state, &anon_vma); >> @@ -1373,6 +1375,12 @@ static int migrate_folio_move(free_folio_t put_new_folio, unsigned long private, >> goto out_unlock_both; >> } >> >> + if (folio_test_large(src) && folio_test_large_rmappable(src) && >> + !data_race(list_empty(&src->_deferred_list))) { > > We usually check order > 1, before accessing _deferred_list, because it is in > subpage 2. > > I am not sure why we don't do it here. Do I miss something? Valid point! non-anon folios could trigger that. -- Cheers, David