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 6A0D6270EDF; Tue, 25 Aug 2026 08:04:39 +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=1787645081; cv=none; b=aeFlDjf5vfWw/rw62VDcUQjEppArZq6xBebLuQRdL3k6mpa6ntBGqsEP9so5VD6tSa3uTIzGNUfmaZk+kqXEHDbqAzSqXcDpd1iIsDkHXPecMXl/ZIZPnTEV1FTNQ/DUjgx0CZGe71wCDbnAk29yEwcsdNJuSobeQrlGrBjol/s= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1787645081; c=relaxed/simple; bh=1urvsIoMlF1eWYcO18v9TlZlqUtgA7NtzjOsZ2p6X38=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=YHMgNbYZoJLZKiORneTpxpPr0jcYsrdcONPaKLFYreKLu/vqqaCQ8whVq9YJ80DojJRQr1j6j4+tjQqRmrVYrZcGRrgjcOJtlHgu0TxyhMX6HWKkl3bKPH3AyR81stRvPc3N655GPJ006vSpXHWXxGmx+iqq4jMgQdlfMw+GdSo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=SOgh1FFa; 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="SOgh1FFa" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6EA211F00A3A; Tue, 25 Aug 2026 08:04:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1787645079; bh=/MaN5UZb6e671DzcVquD6HpICimiFBgIihH7ywUhh1o=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=SOgh1FFa3rCTdan8VrIPmUNWe+htDMxlO5ZSqRaj47x7pRumLA+mRbBR6s6zdnSd6 thToeAXogSG+RtEzRPhlajHf6wrSZ9mwfTM+q8JE8doYh6YGHNVTQaIp73CvdY08w5 N40m+QHqdvS/ZG1S6ffvb2ryETrybHMRtL1qlhjDtz6Uc0O78/7M83KGIP3MViRcqx 2h8Uc6FuQFIMP6cj9FgT+r1gMuoY08mwfFMzghLjEvFdvRPJPZ9EqeeHPpAU1MOw06 jm2f31WAZLGOr2z77Ci4XaymCqtz3Jo7bRmKXYPZtBUsydotjUle0i2/JdCBOgEZWn QMvjXlVLsVVAQ== Message-ID: <2614286d-19ed-4848-8ce6-59ebecf19d1d@kernel.org> Date: Tue, 25 Aug 2026 10:04:31 +0200 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/huge_memory: transfer the pmd dirty bit to the folio on zap To: Christoph Hellwig , Pedro Falcato Cc: Kiryl Shutsemau , Lance Yang , usama.arif@linux.dev, hughd@google.com, akpm@linux-foundation.org, baohua@kernel.org, baolin.wang@linux.alibaba.com, dev.jain@arm.com, liam@infradead.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, ljs@kernel.org, nico.pache@linux.dev, ryan.roberts@arm.com, ziy@nvidia.com, nphamcs@gmail.com, hannes@cmpxchg.org, riel@surriel.com, shakeel.butt@linux.dev, kernel-team@meta.com, stable@vger.kernel.org, willy@infradead.org References: <20260820061337.24669-1-lance.yang@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 8/25/26 07:59, Christoph Hellwig wrote: > On Thu, Aug 20, 2026 at 03:10:11PM +0100, Pedro Falcato wrote: >>> Why? Write batching from large folios is a win. >> >> For some context: we were discussing (off-list) the recent report that >> systemd-journald had horrible write amplification, worsed quite a bit >> by large folios. At the moment, there is quite a lot of write amplification, >> but _only_ on mmap writes (if you look at the write(2) paths, you'll see >> write_begin and write_end which tactically only dirty what you actually wrote >> to, block-wise in the BHs or iomap IFS). This doesn't need to be true. > > So don't use mmap to write to storage. That is always a bad idea for > many, many reasons. We should not work around broken applications that > do this, but change them. It only took about 10 years of bad reputation > for MongoDB to finally fix their act, so it should be possible for > systemd as well. I was in contact with systemd folks (and pulled in Willy and Jan) regarding that, and nothing should really block that. -- Cheers, David