From nobody Fri Nov 15 22:24:38 2024 X-Original-To: fs@mlmmj.nyi.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2610:1c1:1:606c::19:1]) by mlmmj.nyi.freebsd.org (Postfix) with ESMTP id 4Xqs5d4ms2z5df5y for ; Fri, 15 Nov 2024 22:24:53 +0000 (UTC) (envelope-from kostikbel@gmail.com) Received: from kib.kiev.ua (kib.kiev.ua [IPv6:2001:470:d5e7:1::1]) (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 mx1.freebsd.org (Postfix) with ESMTPS id 4Xqs5d15tPz4q2y; Fri, 15 Nov 2024 22:24:53 +0000 (UTC) (envelope-from kostikbel@gmail.com) Authentication-Results: mx1.freebsd.org; none Received: from tom.home (kib@localhost [127.0.0.1] (may be forged)) by kib.kiev.ua (8.18.1/8.18.1) with ESMTP id 4AFMOcCp000722; Sat, 16 Nov 2024 00:24:41 +0200 (EET) (envelope-from kostikbel@gmail.com) DKIM-Filter: OpenDKIM Filter v2.10.3 kib.kiev.ua 4AFMOcCp000722 Received: (from kostik@localhost) by tom.home (8.18.1/8.18.1/Submit) id 4AFMOcK9000721; Sat, 16 Nov 2024 00:24:38 +0200 (EET) (envelope-from kostikbel@gmail.com) X-Authentication-Warning: tom.home: kostik set sender to kostikbel@gmail.com using -f Date: Sat, 16 Nov 2024 00:24:38 +0200 From: Konstantin Belousov To: Andriy Gapon Cc: freebsd-fs Subject: Re: tmpfs loses (sub-page chunks of) data? Message-ID: References: List-Id: Filesystems List-Archive: https://lists.freebsd.org/archives/freebsd-fs List-Help: List-Post: List-Subscribe: List-Unsubscribe: Sender: owner-freebsd-fs@FreeBSD.org MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Spam-Status: No, score=-1.0 required=5.0 tests=ALL_TRUSTED,BAYES_00, DKIM_ADSP_CUSTOM_MED,FORGED_GMAIL_RCVD,FREEMAIL_FROM, NML_ADSP_CUSTOM_MED autolearn=no autolearn_force=no version=4.0.1 X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on tom.home X-Rspamd-Pre-Result: action=no action; module=replies; Message is reply to one we originated X-Spamd-Result: default: False [-4.00 / 15.00]; REPLY(-4.00)[]; ASN(0.00)[asn:6939, ipnet:2001:470::/32, country:US] X-Rspamd-Queue-Id: 4Xqs5d15tPz4q2y X-Spamd-Bar: ---- On Fri, Nov 15, 2024 at 02:43:22PM +0200, Andriy Gapon wrote: > > We have a number of servers based on FreeSBD 13.3 that initially write some > data to files on tmpfs and then the files are dispatched elsewhere. The > writes are done by appending variable sized records to a file. There are no > seeks or overwrites. > > I observe that occasionally (very rarely indeed given the amount of data > produced) we get a corrupted file. > > In all cases so far the corruption follows the same pattern: data range from > the end of a record until the next page-aligned boundary is zeroed out. > That is, good data always continues from an offset which is multiple of 4096 > and the zeroed area never crosses such offsets. > > Because of the page boundary, I have a suspicion that either tmpfs or, > perhaps, the broader VM subsystem might have a race where writing to a page > does not mark it dirty. Maybe this is related to paging out of a tmpfs page > to the swap. > > The problem is that I have never been able to observe this happening, the > corruption gets detected after the fact, hours after it occurs. > > If anyone could suggest any areas / changes / techniques to explore the > problem, I would be much obliged. Do you have swap enabled on the problematic machines? Are the files mapped, do you write or read through map?