From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by smtp.lore.kernel.org (Postfix) with ESMTP id 5B38AC433EF for ; Wed, 12 Jan 2022 12:29:23 +0000 (UTC) Received: by kanga.kvack.org (Postfix) id B62AA6B0156; Wed, 12 Jan 2022 07:29:22 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id AEC126B0157; Wed, 12 Jan 2022 07:29:22 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 98C006B0158; Wed, 12 Jan 2022 07:29:22 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0174.hostedemail.com [216.40.44.174]) by kanga.kvack.org (Postfix) with ESMTP id 84CE76B0156 for ; Wed, 12 Jan 2022 07:29:22 -0500 (EST) Received: from smtpin14.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with ESMTP id 331DA9275C for ; Wed, 12 Jan 2022 12:29:22 +0000 (UTC) X-FDA: 79021565364.14.657C4E9 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.129.124]) by imf17.hostedemail.com (Postfix) with ESMTP id BE0A940008 for ; Wed, 12 Jan 2022 12:29:21 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1641990561; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=zJjZLA05/EVAnL9glMI370u+RyOka7ubh9bOziaJLmU=; b=TKM6KCoQcZWFa/+cvsAmKQdpMa6Q9dVP5fRoXhwmwnJxAD2Bw5C8uIOWwbCHR/hT6vVWQq B+qToo4cdWNyp/x/IhX9wffUT7bbWBRRpWW3SgmHVIHmOZhu033cdN1mand9khTHz7gkHl DD6rGaLMS8EWsD+V3UcRSAahFWwLA3s= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-7-s4u3pdpIN4axsi6-rARwNg-1; Wed, 12 Jan 2022 07:29:18 -0500 X-MC-Unique: s4u3pdpIN4axsi6-rARwNg-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id EFA29363A5; Wed, 12 Jan 2022 12:29:16 +0000 (UTC) Received: from file01.intranet.prod.int.rdu2.redhat.com (file01.intranet.prod.int.rdu2.redhat.com [10.11.5.7]) by smtp.corp.redhat.com (Postfix) with ESMTPS id D2C1E708C9; Wed, 12 Jan 2022 12:29:12 +0000 (UTC) Received: from file01.intranet.prod.int.rdu2.redhat.com (localhost [127.0.0.1]) by file01.intranet.prod.int.rdu2.redhat.com (8.14.4/8.14.4) with ESMTP id 20CCTCNb027823; Wed, 12 Jan 2022 07:29:12 -0500 Received: from localhost (mpatocka@localhost) by file01.intranet.prod.int.rdu2.redhat.com (8.14.4/8.14.4/Submit) with ESMTP id 20CCTB7j027819; Wed, 12 Jan 2022 07:29:11 -0500 X-Authentication-Warning: file01.intranet.prod.int.rdu2.redhat.com: mpatocka owned process doing -bs Date: Wed, 12 Jan 2022 07:29:11 -0500 (EST) From: Mikulas Patocka X-X-Sender: mpatocka@file01.intranet.prod.int.rdu2.redhat.com To: Hugh Dickins cc: Lukas Czerner , Zdenek Kabelac , linux-mm@kvack.org, linux-fsdevel@vger.kernel.org Subject: Re: unusual behavior of loop dev with backing file in tmpfs In-Reply-To: <5e66a9-4739-80d9-5bb5-cbe2c8fef36@google.com> Message-ID: References: <20211126075100.gd64odg2bcptiqeb@work> <5e66a9-4739-80d9-5bb5-cbe2c8fef36@google.com> User-Agent: Alpine 2.02 (LRH 1266 2009-07-14) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: BE0A940008 X-Stat-Signature: 8i64qc73ukn3kuystp4ygbeci4uncrn8 Authentication-Results: imf17.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=TKM6KCoQ; dmarc=pass (policy=none) header.from=redhat.com; spf=none (imf17.hostedemail.com: domain of mpatocka@redhat.com has no SPF policy when checking 170.10.129.124) smtp.mailfrom=mpatocka@redhat.com X-HE-Tag: 1641990561-687817 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: On Tue, 11 Jan 2022, Hugh Dickins wrote: > But what is asynchronously reading /dev/loop0 (instantiating pages > initially, and reinstantiating them after blkdiscard)? I assume it's > some block device tracker, trying to read capacity and/or partition > table; whether from inside or outside the kernel, I expect you'll > guess much better than I can. > > Hugh That's udev. It reads filesystem signature on every block device, so that it can create symlinks in /dev/disk/by-uuid. If you open the block device for write and close it, udev will re-scan it. Mikulas