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AJvYcCWCUkxpMVtcIUX2OqrymcoPn5U9LB86+6Gltu+KWrQe2qQzCcnZ4yYklhofSUHqFjUDi3pOXi6tvg==@kvack.org X-Gm-Message-State: AOJu0Ywvv4N5VU9IHsbSJBI+WbIrBqVEiF5cppzoWbFPt/T21QNDDpOD 7xBNOmRAM1DKScsJifhmx6H7cAkn/xWjD6jbaCUkktCz8v4ZevMK24aPNqxCUJ/QF+F5s0hNF65 6WTdsQdVUd4ARj+baWINRz2Qf4no= X-Gm-Gg: ASbGncs3FNI6vn2DmeWH9WJ/8rj2cK8Dsjam2ttUQlvTCKQqiCTorD3qkSvsvZpj78g zL69dQjZF6KtKRLB9Th/BGqIEso/UtTZSoFHihk+CStKxL2BlrVY= X-Google-Smtp-Source: AGHT+IH6zCDnNnGoZfdW8RVHy8XiGQEPQ/0uz30GpY/GODEywo99XsjckmFy9IqpPlWEHstk9bx5pRgRx7iE91r4wuk= X-Received: by 2002:a05:6402:2105:b0:5d8:8292:5674 with SMTP id 4fb4d7f45d1cf-5db7dc69528mr12111885a12.7.1737392367451; Mon, 20 Jan 2025 08:59:27 -0800 (PST) MIME-Version: 1.0 References: <20250119103205.2172432-1-mjguzik@gmail.com> <55qxyg2diynlelvdzorhvtk4omfcobarious3fkxh4n33oezod@sju7s6sebec3> In-Reply-To: <55qxyg2diynlelvdzorhvtk4omfcobarious3fkxh4n33oezod@sju7s6sebec3> From: Mateusz Guzik Date: Mon, 20 Jan 2025 17:59:15 +0100 X-Gm-Features: AbW1kvZq74DcCKaOaaVNpiz27xXeCSDxs2uqT_K742SG4CHaeD43A9tIibZ7vdY Message-ID: Subject: Re: [RESEND PATCH] fs: avoid mmap sem relocks when coredumping with many missing pages To: Jan Kara Cc: brauner@kernel.org, viro@zeniv.linux.org.uk, linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, tavianator@tavianator.com, linux-mm@kvack.org, akpm@linux-foundation.org Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Stat-Signature: bk4fajycxsc38n1onx3r8zbjc7uwx6tn X-Rspamd-Queue-Id: 426E640003 X-Rspam-User: X-Rspamd-Server: rspam06 X-HE-Tag: 1737392369-947791 X-HE-Meta: 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 Te9sfkPB cLNacuH5NdKd3U6dzPJoUv0fLeZdxiNao7bIby7Y9HZLTNKJ6yZJsTs/8bbdk1TSDiLWhGfF6te6qPcvUIZ+a0tu7Ty/0DAeCUk7mm4pmLN71/a+PM7C7nN0kVj95KIL23zliD+Ze/L+/t1KxVdImkHCr5B6HKF4V4QKzSmU0p3q2uZJBUIesK+3IE1ZyZZirMibJxe3aKI0tYLHOz4qp5W7P1fch2NMOl0mKJzkU5Ne/FlxYAlIAU0d/2XGHwrTQkw/Hhnm7wIAEi7cfJWlmGtThAMPuq+ZoD6ppf2klLeMDRv6t09eITlPTcsayo04BNrXofH1Rk5VuJCcf/sGXkz8XWuzK+xhA56Z0ROqRJkEbcH0yVCIyjRa7aA== X-Bogosity: Ham, tests=bogofilter, spamicity=0.007294, 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 Mon, Jan 20, 2025 at 5:00=E2=80=AFPM Jan Kara wrote: > BTW: I don't see how we could fundamentally move away from page-sized > iteration because core dumping is "by definition" walking page tables and > gathering pages there. But it could certainly be much more efficient if > implemented properly (e.g. in the example above we'd see that most of PGD > level tables are not even allocated so we could be skipping 1GB ranges of > address space in one step). > I was thinking find first allocated page starting at X, then fill in the gap from the last one as required by the format. Rinse & repeat until the entire vma is covered. Surely finding the next page which is known to be there is going to be cheaper than specifically checking if a given page is there. --=20 Mateusz Guzik