From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from casper.infradead.org (casper.infradead.org [90.155.50.34]) (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 F18D42E173B; Fri, 1 May 2026 14:57:13 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=90.155.50.34 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777647436; cv=none; b=NlF3vnCEnFhzSe+QDJS/yhgHpzjBR//UcPidoPv+eA7NPT3KH0efs9APmeueny5tVAwlzdioqDY/SzSiRz8OljpcNWjrWYjZuNUojEXVR76wbBcFvwTkA1geFhAg+3raqI9jfglvtc/lkyiLRGIsT52G/p1dnWnZL2cO61zgPhk= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1777647436; c=relaxed/simple; bh=ds5qEdrw885QHRjvKKYO1xHswqo7gHLI9viitfcmqVg=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=rzoIG24mBrbEDvp2oAM1L6B1F/8lFiWczTQXqxBTIkW/cNAc31BcqWvdDG9yRbEYhfNHFDhBgfLyBKolDmbneq/3tZE/9Q0KGWE/QMXOMx/WWDUktNh7pWPircSdRlW98AhasbGyy6QjXWIP1FoB9jclHXRUtFgCnyux2lYHFmU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=infradead.org; spf=none smtp.mailfrom=infradead.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b=Er8GF8z4; arc=none smtp.client-ip=90.155.50.34 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=infradead.org Authentication-Results: smtp.subspace.kernel.org; spf=none smtp.mailfrom=infradead.org Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=infradead.org header.i=@infradead.org header.b="Er8GF8z4" DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=infradead.org; s=casper.20170209; h=In-Reply-To:Content-Type:MIME-Version: References:Message-ID:Subject:Cc:To:From:Date:Sender:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description; bh=GWaEOZ6T8RZshC5VNeX+VR+c38seOstsZgFtVZK1Yb0=; b=Er8GF8z4i4fcdoqldcSz6UdIrK 0uV2fMmb401OPsbWUDQlEgY0WImYvRoaOS/51Kt7cci4PwM0IwWZmDRUbGXw7O9IkTUTcXx4Dq2Om 1ySnKP5ZPsmA0cdTKwQEUsbejJKOkDxp+xsnqOc9et7bCG9WzZFKFYNxcz4UjijcH9lNIaYGg9axV D8CvZuRnVnBvGs0WeFCpwaRxMrcj+ZmM+kVA2Q+aDmR35tDfpqtDlNjfzVDU0ieNT7dT3nkuFY8KO oBaeuIlQkfSbM8D3+gtqA/Kl4BULEQcG2OPtDBswRpN88NbjoIlZE7bl29JItAlrzNVWRNazfWERT lB1uWyaw==; Received: from willy by casper.infradead.org with local (Exim 4.98.2 #2 (Red Hat Linux)) id 1wIpIN-00000008wbR-3iIK; Fri, 01 May 2026 14:56:48 +0000 Date: Fri, 1 May 2026 15:56:47 +0100 From: Matthew Wilcox To: Barry Song Cc: akpm@linux-foundation.org, linux-mm@kvack.org, david@kernel.org, ljs@kernel.org, liam@infradead.org, vbabka@kernel.org, rppt@kernel.org, surenb@google.com, mhocko@suse.com, jack@suse.cz, pfalcato@suse.de, wanglian@kylinos.cn, chentao@kylinos.cn, lianux.mm@gmail.com, kunwu.chan@gmail.com, liyangouwen1@oppo.com, chrisl@kernel.org, kasong@tencent.com, shikemeng@huaweicloud.com, nphamcs@gmail.com, bhe@redhat.com, youngjun.park@lge.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, loongarch@lists.linux.dev, linuxppc-dev@lists.ozlabs.org, linux-riscv@lists.infradead.org, linux-s390@vger.kernel.org Subject: Re: [PATCH v2 0/5] mm: reduce mmap_lock contention and improve page fault performance Message-ID: References: <20260430040427.4672-1-baohua@kernel.org> Precedence: bulk X-Mailing-List: linux-s390@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: On Fri, May 01, 2026 at 06:49:58AM +0800, Barry Song wrote: > 1. There is no deterministic latency for I/O completion. It depends on > both the hardware and the software stack (bio/request queues and the > block scheduler). Sometimes the latency is short; at other times it can > be quite long. In such cases, a high-priority thread performing operations > such as mprotect, unmap, prctl_set_vma, or madvise may be forced to wait > for an unpredictable amount of time. But does that actually happen? I find it hard to believe that thread A unmaps a VMA while thread B is in the middle of taking a page fault in that same VMA. mprotect() and madvise() are more likely to happen, but it still seems really unlikely to me.