From owner-freebsd-bugs@freebsd.org Mon Sep 21 17:16:14 2020 Return-Path: Delivered-To: freebsd-bugs@mailman.nyi.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2610:1c1:1:606c::19:1]) by mailman.nyi.freebsd.org (Postfix) with ESMTP id D78283F6D21 for ; Mon, 21 Sep 2020 17:16:14 +0000 (UTC) (envelope-from bugzilla-noreply@freebsd.org) Received: from mailman.nyi.freebsd.org (unknown [127.0.1.3]) by mx1.freebsd.org (Postfix) with ESMTP id 4BwB1B5RzQz4Wqt for ; Mon, 21 Sep 2020 17:16:14 +0000 (UTC) (envelope-from bugzilla-noreply@freebsd.org) Received: by mailman.nyi.freebsd.org (Postfix) id B91863F6CAC; Mon, 21 Sep 2020 17:16:14 +0000 (UTC) Delivered-To: bugs@mailman.nyi.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2610:1c1:1:606c::19:1]) by mailman.nyi.freebsd.org (Postfix) with ESMTP id B8DC03F6D20 for ; Mon, 21 Sep 2020 17:16:14 +0000 (UTC) (envelope-from bugzilla-noreply@freebsd.org) Received: from mxrelay.nyi.freebsd.org (mxrelay.nyi.freebsd.org [IPv6:2610:1c1:1:606c::19:3]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256 client-signature RSA-PSS (4096 bits) client-digest SHA256) (Client CN "mxrelay.nyi.freebsd.org", Issuer "Let's Encrypt Authority X3" (verified OK)) by mx1.freebsd.org (Postfix) with ESMTPS id 4BwB1B4b67z4X0M for ; Mon, 21 Sep 2020 17:16:14 +0000 (UTC) (envelope-from bugzilla-noreply@freebsd.org) Received: from kenobi.freebsd.org (kenobi.freebsd.org [IPv6:2610:1c1:1:606c::50:1d]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (Client did not present a certificate) by mxrelay.nyi.freebsd.org (Postfix) with ESMTPS id 8273D119B5 for ; Mon, 21 Sep 2020 17:16:14 +0000 (UTC) (envelope-from bugzilla-noreply@freebsd.org) Received: from kenobi.freebsd.org ([127.0.1.5]) by kenobi.freebsd.org (8.15.2/8.15.2) with ESMTP id 08LHGE1d077585 for ; Mon, 21 Sep 2020 17:16:14 GMT (envelope-from bugzilla-noreply@freebsd.org) Received: (from www@localhost) by kenobi.freebsd.org (8.15.2/8.15.2/Submit) id 08LHGE0l077584 for bugs@FreeBSD.org; Mon, 21 Sep 2020 17:16:14 GMT (envelope-from bugzilla-noreply@freebsd.org) X-Authentication-Warning: kenobi.freebsd.org: www set sender to bugzilla-noreply@freebsd.org using -f From: bugzilla-noreply@freebsd.org To: bugs@FreeBSD.org Subject: [Bug 246886] [sendfile] Nginx + NFS or FUSE causes VM stall Date: Mon, 21 Sep 2020 17:16:14 +0000 X-Bugzilla-Reason: AssignedTo X-Bugzilla-Type: changed X-Bugzilla-Watch-Reason: None X-Bugzilla-Product: Base System X-Bugzilla-Component: kern X-Bugzilla-Version: 12.1-RELEASE X-Bugzilla-Keywords: X-Bugzilla-Severity: Affects Only Me X-Bugzilla-Who: glebius@FreeBSD.org X-Bugzilla-Status: New X-Bugzilla-Resolution: X-Bugzilla-Priority: --- X-Bugzilla-Assigned-To: bugs@FreeBSD.org X-Bugzilla-Flags: X-Bugzilla-Changed-Fields: Message-ID: In-Reply-To: References: Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Bugzilla-URL: https://bugs.freebsd.org/bugzilla/ Auto-Submitted: auto-generated MIME-Version: 1.0 X-BeenThere: freebsd-bugs@freebsd.org X-Mailman-Version: 2.1.33 Precedence: list List-Id: Bug reports List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 21 Sep 2020 17:16:14 -0000 https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=3D246886 --- Comment #54 from Gleb Smirnoff --- Then that's a crazy mix of subsystems involved! Here goes description of how nginx combines aio and sendfile. When sendfile= (2) returns EBUSY, nginx would do aio_read(2) of 1 byte out of the file, and us= e a side effect of the page being cached, then it would retry sendfile again. Note, that EBUSY from sendfile in FreeBSD 11 and before means totally diffe= rent thing than EBUSY from sendfile on FreeBSD 12 and after. On older versions E= BUSY means that SF_NODISKIO was set on request and file is not in memory. On new versions EBUSY is a soft error that means page is busy (again SF_NODISKIO is set). The busy condition would go away in a few milliseconds. However, nginx doesn't differentiate between versions of FreeBSD and always does this aio_read() of 1 byte. It is harmless on newer versions of FreeBSD and just = adds a small delay before retry. At Netflix we have removed this code from nginx= and in case of EBUSY we just retry after a timer, so we don't use aio. It is entirely possible that problem shows up only when aio_read() and send= file are combined on the same region of a file on NFS or FUSE :( --=20 You are receiving this mail because: You are the assignee for the bug.=