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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 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 X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: C998E20008 X-Stat-Signature: u4mjekgcuajzx8wccykeckxshy15zznr X-HE-Tag: 1787645079-177548 X-HE-Meta: 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 +W9PCrF9 v4HHCdzXbKI8M4N7DpQJ4J4OFzCrVLGP913H8uON1341x5s2xbNSeMd73lInx7W7W3xcuuiMo3f+ONk+UVo9rLFI4j3B7/H1zAsZiYR0d6oi9dWR4be/U9uiC/IecB1xqxs0jihuEhFqAvL7/OCUAdMEemBvENpyH1Q0i6SxqP2XUXzSXNjFVLjdmdhqqjaJSEvNJwmDTtq5yHl7xtURBYLRvVEqlIw4zijZjsC5XLUtGEzqSutgGEI/R03aWd18WyghX7jJrrT+G+PhITnfyoYd+07MWwHGEO6QupIeuOqQ8gH6G8c2sdK6SMQ== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: 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