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[209.85.218.52]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-b4865e77427sm473769966b.36.2025.10.03.09.40.33 for (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 03 Oct 2025 09:40:34 -0700 (PDT) Received: by mail-ej1-f52.google.com with SMTP id a640c23a62f3a-afcb7ae6ed0so429253366b.3 for ; Fri, 03 Oct 2025 09:40:33 -0700 (PDT) X-Forwarded-Encrypted: i=1; AJvYcCWDXCceURg422pru6JyPUIOkVaePl4kaJ5jUXAEA8CLpKNrdB3/QFMNQVF/Hzryql11iSmvZ8gHqw==@kvack.org X-Received: by 2002:a17:907:7f25:b0:b37:4f78:55b2 with SMTP id a640c23a62f3a-b49c3d74babmr424650466b.34.1759509633396; Fri, 03 Oct 2025 09:40:33 -0700 (PDT) MIME-Version: 1.0 References: In-Reply-To: From: Linus Torvalds Date: Fri, 3 Oct 2025 09:40:17 -0700 X-Gmail-Original-Message-ID: X-Gm-Features: AS18NWBsgBCnrJzzu5xoBdIh2bX5YeDo-15f38HyVBOhspvW89C8BBlXICWbE3s Message-ID: Subject: Re: Optimizing small reads To: Kiryl Shutsemau Cc: Matthew Wilcox , Luis Chamberlain , Linux-MM Content-Type: text/plain; charset="UTF-8" X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 0AC9D4000F X-Stat-Signature: 984pimwywtpxwsa6654tmhe3ofw3xpg6 X-Rspam-User: X-HE-Tag: 1759509636-607109 X-HE-Meta: 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 88IEmboW 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, 3 Oct 2025 at 09:18, Linus Torvalds wrote: > > That was one of the theories and it might be the right one. There was > some discussion about having a sequence number. It's a long time ago, > I forget. Ok, this bothered me. So I went back. Damn. I actually mentioned that in the original submission (well, actually the reply after I had booted into it [1]): "And even then there's the question about replacing the same folio in the same spot in the xarray. I'm not convinced it is worth worrying about in any reality we care about, but it's _technically_ all a bit wrong" but then I left it because I was hoping somebody else would deal with it. And I brought up the patch again several months later, but by then I had obviously repressed that issue. So yeah, I think that's it, and I even knew about it originally, but in my incompetence I had entirely forgotten. And by "that's it", I obviously mean that there might be something else going on too. How about a sequence number in 'struct address_space' that gets incremented by removing folios? Or even in 'struct xarray': it would always be protected by xa_lock, so it doesn't even need any new atomicity... Anyway, I think you're entirely right, Kirill. And sorry for wasting peoples time when I _should_ have remembered about this. Linus https://lore.kernel.org/all/CAHk-=whFzKO+Vx2f8h72m7ysiEP2Thubp3EaZPa7kuoJb0k=ig@mail.gmail.com/ [1]