From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id E6B163630AE for ; Fri, 6 Mar 2026 16:24:02 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772814243; cv=none; b=PpKjGlotxDoNnncoiz5OUBVvHUIid/iB/X6q9IP4997E6zT94RW7lkYIweMTibrZlZdOFVLkFGLqB2HPV1u+rwuGcN23dtqH+ZSol4eRCCIFw+9Tsha43sZH4gf7XvHs3H/VPV0pceeMsXtnkHd7y3RD/IY4RPO1lhRNQCBX/EI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772814243; c=relaxed/simple; bh=9h1lyEgM+GxS6qSq98yQHb8auw7NBPQnSoVt7zW8kt8=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=o/TIe8O/xw9ZoETX1eHNY9L6eErioxc+dYYIFHsD6zK/Uu1QfDhS7PLsPshextpqDmFEZB6r89x+ZV0gnsGJZnKabbPqLlEEaqPI/Tg7zIPSZehrOYDHxD+QRugWFX7ARwQAueMMiJ/K6MFsgrFNWQ0mfOxTc1pU0uofd8bpbWs= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=OcMGJfRO; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="OcMGJfRO" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 34E00C4CEF7; Fri, 6 Mar 2026 16:23:57 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1772814242; bh=9h1lyEgM+GxS6qSq98yQHb8auw7NBPQnSoVt7zW8kt8=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=OcMGJfROeAkAi1TOw9J5rtJAw0pKovKAG4Ldl+hW/+sY1kFAGs8x3yWre4Lvy4neS Muvg76OrE4AlupG60VCKZV1KV/8SVY5OiABXbDlA4Xn5sFlS2XVSAymAP47IAJpICq wEdky5z2ghiwYQJ7rOyMek/zUQo0ew3Wa0sI71R9SZQatTP0OYfqgnLlB8PYH4etu2 jsN3d1b+elZCOdY8Qz1GVjorHwPikLm/LS0QtoznHuqtYNtlpoXkLASxJhNkJJOHAI 2aDORfGNoz2/RvQgbRlzv7SvH+hvEWIw3jMCI5vTMfHnX50072mMTzvGdRV7AfHkCr 6jfv5dHkyo3iQ== Message-ID: Date: Fri, 6 Mar 2026 17:23:53 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] mm: migrate: requeue destination folio on deferred split queue To: Usama Arif , Zi Yan Cc: Andrew Morton , npache@redhat.com, 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: <20260306133556.2051251-1-usama.arif@linux.dev> <64051a59-680f-40ae-b291-b884aeb7c77b@linux.dev> <993B37FF-29E1-41F5-A1E8-F38B9CD24478@nvidia.com> <28e48b47-f215-4e4a-b55a-01dbf293ff35@linux.dev> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit On 3/6/26 17:15, Usama Arif wrote: > > > On 06/03/2026 14:46, Zi Yan wrote: >> On 6 Mar 2026, at 9:12, Usama Arif wrote: >> >>> >>> Yes you are right. How about something like below? We also won't need to check >>> for anon and non-device folios with this as we only set the the flag if it was >>> already on deferred_split list. >> >> BTW, migrate_pages() tries to split partially mapped folios before migration[1], >> so what remains in the deferred_list would be: >> >> 1. partially mapped but with a pin, >> 2. fully mapped but potentially underused. >> > > Yes, thats right. > >> I wonder if you want to do an underused scan before migration and try to split >> underused THPs. > > hmm, I think we should keep THPs as is if there is no memory pressure (proactive > or otherwise). Scanning THPs for zeros has a cost and we would also lose the benefit > of THPs when we dont need memory. > >> Or to avoid this additional scan, find a way of detecting >> zero pages at page copy time and split it after migration. >> > > Yeah but I think we lose the benefits of THPs after migration when we dont need > additional memory? > >> Anyway, it seems that all large folios are in this deferred_list. Maybe, like >> David suggested in his LSFMM proposal, we should scan large folios on LRU lists >> at reclaim time instead, since there is not much difference between deferred_list >> and LRU lists right now. >> > > Yeah the THP shrinker is a very basic implementation and there are a lot of > >> >> [1] https://elixir.bootlin.com/linux/v6.19.3/source/mm/migrate.c#L1840 >> > > Also Johannes pointed out its not great storing this information in page flags, > we can just keep it as local variable. This is what the patch would look like: Much cleaner. -- Cheers, David