From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 C1B3037F33D; Thu, 27 Aug 2026 20:27:11 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787862434; cv=none; b=JQmLfkyPdLWUnwocI6x/yt/4tU1pfsRZ/eAToiQ9QfL/i9/ppoksseOZDorQoIRhsuEStsu1Iq1D5N1iQZTOXc6K8eSUAfj4NGPfd60eU+l0dPnZwxyD+FDIWrYlQ9ToW8BQZ8gALiHLH9WwafFbAnjGgcU6rlW3oRHqPIpdD/8= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787862434; c=relaxed/simple; bh=8JERRk4eycKxps6u6lqA4pRwfLdjT0fCroEkw4dtSAQ=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=iXNKZefza4OYsphdEWbT2CZBB6nMHovLJVcwEgLelSR+sZx2a2aZFjWrxgZRhIFj+rn9NXHli+muzBr6vEttBJKJb8S6JwW9R3HST1BIAQosdoED7+F5XZpJNPTOd/QJHMYwxc8IpeKiqkcusG90dWZ9tnWVz2Yj84fNkIHOycQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=mCbG6wIr; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="mCbG6wIr" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 544C81F000E9; Thu, 27 Aug 2026 20:27:00 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1787862430; bh=1L3yxEZbWCvg5LUmRwP8ZDavWBk+Bf+rg5djBphl/1s=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=mCbG6wIrrG+wf+wFiK8+ak/XJFOgf02RCcuYCcZpXC3tCVV+oMUfKaZuB+PLZA+/Q bBqvFU/RlaUmb8rzrh233tGbgtj+5cZ0lX0cLf5Szk2Ley1p8mI+hxkXzKjsOrDc0w Qoy1yiXqTErnp5LLKhzzzEFdKekHfvujE350xJ3hULVdozTJkJOKwmJXxy2A1oe7sS g/j3UNZG2GmeAmc5QUephEnpY08momDvCUPbcEfTBieqPovU8lMhrtt0w11NopdCLg ztNGnkpYFo4vTWWTk4/hmYbyKYy05qkqR/VDmAd6iHbVWogmnkqC0QWHFftwsTlb2q 5YntX49ZLP4pA== Message-ID: <443ab5b5-2d47-4ffe-bfa2-15e47ff7469c@kernel.org> Date: Thu, 27 Aug 2026 22:26:58 +0200 Precedence: bulk X-Mailing-List: linux-fsdevel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 20/25] s390/fbatch: no lru_add_drain_all() in s390_wiggle_split_folio() To: Claudio Imbrenda , Hugh Dickins Cc: Andrew Morton , Ackerley Tng , Alexander Viro , Baolin Wang , Barry Song , Binbin Wu , Christian Brauner , Christoph Hellwig , Christoph Lameter , JP Kobryn , Jan Kara , Jens Axboe , Johannes Weiner , Kairui Song , Kiryl Shutsemau , Lance Yang , Leonardo Bras , Lorenzo Stoakes , Marcelo Tosatti , Matthew Wilcox , Mel Gorman , Miaohe Lin , Michal Hocko , Minchan Kim , Muchun Song , Oscar Salvador , Peter Zijlstra , Qi Zheng , Rik van Riel , Sebastian Andrzej Siewior , Shakeel Butt , Suren Baghdasaryan , Vlastimil Babka , Yang Shi , Yu Zhao , Zach O'Keefe , Zi Yan , linux-block@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org References: <14a16945-529b-8bc0-ab38-3ea97e54e223@google.com> <7bf68e7b-f88c-6ca9-39ab-e9fedab0c8be@google.com> <20260826155722.0198d3ce@p-imbrenda> <2319f670-fe0b-f032-c0dc-486cbec0f3e1@google.com> <20260827145502.2fb4505b@p-imbrenda> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit >> I most certanly don't know s390 or that code well enough to guarantee >> you that no stray references to mapped folios can remain there. What I >> can guarantee is that no references, of the kind which lru_add_drain_all() >> used to be needed to remove, can exist there: so there will no longer >> be any point in s390 (or others) calling it for that reason, to help >> split_folio() to succeed. > > we are not using it to help split_folio() succeed (although that's a > pleasant side effect). We need it even for small pages, to guarantee > that no extra reference from LRU is present on the page. Just to clarify: the LRU cache might have references (IOW a pointer) to the folio BUT the refcount of the folio is not increased. And that's what s390x cares about. [...] > >> there was an earlier time when mm did not enforce that; and Barry >> is currently looking to relax that, so the limitation intended for >> pmd-sized folios is no longer forced on the smallest large folios. >> >> If Barry's relaxation goes in before my drainage changes, then >> there is value in that s390 lru_add_drain_all() in the interim. I think we should get lru cache references sorted before we consider using them for (m)THP. If we realize that this series here cannot land any time soon, we can reconsider. -- Cheers, David