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 X-Spam-Level: X-Spam-Status: No, score=-8.0 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id D668EC3A59B for ; Mon, 19 Aug 2019 05:14:37 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 8F87121852 for ; Mon, 19 Aug 2019 05:14:37 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=gmx.net header.i=@gmx.net header.b="f7dnwXqz" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726491AbfHSFOc (ORCPT ); Mon, 19 Aug 2019 01:14:32 -0400 Received: from mout.gmx.net ([212.227.15.19]:47149 "EHLO mout.gmx.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725790AbfHSFOb (ORCPT ); Mon, 19 Aug 2019 01:14:31 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=gmx.net; s=badeba3b8450; t=1566191663; bh=JuUN0SLO7/1VDIszJlkFJSmCapxzCX0AnIL26Gry0MM=; h=X-UI-Sender-Class:Subject:To:Cc:References:From:Date:In-Reply-To; b=f7dnwXqz/CtqXHWN4yzMHSHByBK+JGsvybCo5/8foueRzwG1NdfAZy4Hq1lkvf9g5 OxTJ2wCCAWexuOfaNnSwd64UsO1piGSzZvQ/H3KRjPHYVzqaq9EKqIaymU7XczlGXl /C3qiclTiRGegce9NGX+YVlQVw8sOoq4NaQDmtFk= X-UI-Sender-Class: 01bb95c1-4bf8-414a-932a-4f6e2808ef9c Received: from [0.0.0.0] ([54.250.245.166]) by mail.gmx.com (mrgmx003 [212.227.17.184]) with ESMTPSA (Nemesis) id 0M3j17-1iHf4x3HdZ-00rJJM; Mon, 19 Aug 2019 07:14:23 +0200 Subject: Re: [PATCH v2] btrfs: transaction: Commit transaction more frequently for BPF To: fdmanana@gmail.com, Qu Wenruo Cc: linux-btrfs References: <20190815080404.20600-1-wqu@suse.com> From: Qu Wenruo Openpgp: preference=signencrypt Autocrypt: addr=quwenruo.btrfs@gmx.com; 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boundary="iP0ZkH1bFp06VDAzmgSL9cDEqlilcYqTq"; protected-headers="v1" From: Qu Wenruo To: fdmanana@gmail.com, Qu Wenruo Cc: linux-btrfs Message-ID: Subject: Re: [PATCH v2] btrfs: transaction: Commit transaction more frequently for BPF References: <20190815080404.20600-1-wqu@suse.com> In-Reply-To: --iP0ZkH1bFp06VDAzmgSL9cDEqlilcYqTq Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable On 2019/8/16 =E4=B8=8B=E5=8D=885:33, Filipe Manana wrote: > On Thu, Aug 15, 2019 at 9:36 AM Qu Wenruo wrote: >> >> Btrfs has btrfs_end_transaction_throttle() which could try to commit >> transaction when needed. >> >> However under most cases btrfs_end_transaction_throttle() won't really= >> commit transaction, due to the hard timing requirement. >> >> Now introduce a new error injection point, btrfs_need_trans_pressure()= , >> to allow btrfs_should_end_transaction() to return 1 and >> btrfs_end_transaction_throttle() to fallback to >> btrfs_commit_transaction(). >> >> With such more aggressive transaction commit, we can dig deeper into >> cases like snapshot drop. >> Now each reference drop of btrfs_drop_snapshot() will lead to a >> transaction commit, allowing dm-logwrites to catch more details, other= >> than one big transaction dropping everything. >> >> Signed-off-by: Qu Wenruo >> --- >> Changelog: >> v2: >> - Add comment to explain why this function is needed >> --- >> fs/btrfs/transaction.c | 18 ++++++++++++++++++ >> 1 file changed, 18 insertions(+) >> >> diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c >> index 3f6811cdf803..8c5471b01d03 100644 >> --- a/fs/btrfs/transaction.c >> +++ b/fs/btrfs/transaction.c >> @@ -10,6 +10,7 @@ >> #include >> #include >> #include >> +#include >> #include "ctree.h" >> #include "disk-io.h" >> #include "transaction.h" >> @@ -749,10 +750,25 @@ void btrfs_throttle(struct btrfs_fs_info *fs_inf= o) >> wait_current_trans(fs_info); >> } >> >> +/* >> + * This function is to allow BPF to override the return value so that= we can >> + * make btrfs to commit transaction more aggressively. >> + * >> + * It's a debug only feature, mainly used with dm-log-writes to catch= more details >> + * of transient operations like balance and subvolume drop. >=20 > Transient? I think you mean long running operations that can span > multiple transactions. >=20 >> + */ >> +static noinline bool btrfs_need_trans_pressure(struct btrfs_trans_han= dle *trans) >> +{ >> + return false; >> +} >> +ALLOW_ERROR_INJECTION(btrfs_need_trans_pressure, TRUE); >=20 > So, I'm not sure if it's really a good idea to have such specific > things like this. > Has this proven useful already? I.e., have you already found any bug us= ing this? >=20 > I often add such similar things myself for testing and debugging, but > because they are so specific, or ugly or verbose, I keep them to > myself. >=20 > Allowing the return value of should_end_transaction() to be > overridden, using the same approach, would be more generic for > example. Forgot to mention there is another function checking this: __btrfs_end_transaction. If btrfs_need_trans_pressure() returns true, __btrfs_end_transaction() will try to commit transaction for btrfs_end_transaction_throttle(). Thanks, Qu >=20 > Thanks. >=20 >> + >> static int should_end_transaction(struct btrfs_trans_handle *trans) >> { >> struct btrfs_fs_info *fs_info =3D trans->fs_info; >> >> + if (btrfs_need_trans_pressure(trans)) >> + return 1; >> if (btrfs_check_space_for_delayed_refs(fs_info)) >> return 1; >> >> @@ -813,6 +829,8 @@ static int __btrfs_end_transaction(struct btrfs_tr= ans_handle *trans, >> >> btrfs_trans_release_chunk_metadata(trans); >> >> + if (throttle && btrfs_need_trans_pressure(trans)) >> + return btrfs_commit_transaction(trans); >> if (lock && READ_ONCE(cur_trans->state) =3D=3D TRANS_STATE_BLO= CKED) { >> if (throttle) >> return btrfs_commit_transaction(trans); >> -- >> 2.22.0 >> >=20 >=20 --iP0ZkH1bFp06VDAzmgSL9cDEqlilcYqTq-- --5Hiz1LoLsUsCyIomCkUSXPgE8nLr9Rg1d Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQEzBAEBCAAdFiEELd9y5aWlW6idqkLhwj2R86El/qgFAl1aMCoACgkQwj2R86El /qiEHwf/ZYpMGzFR03dAbvY+BvY73rgDDAaNQ7lfNyMuMNjJC8d8Ah2dvjATMZVY MxwKieryuCs58W4je1X51vO+1OouebuPdMR2RAFqPC4bkmfmRSKP2KHnSCc1iAvg O0/6r4eaubjzeuKpa7mE6QOP0h11rlG2CGT9d7IVAgpfTEW++X/jXnbSp7KvteeS VPoSAytOJomOzTaYivH60SofJSXd9VTMaEFUtCFLKV8J6vo3ZE+KePTg8j2XzknE Em73lBJSyOK9n0L/PzF0AFCqd2D+v95E0nMVOuS8PUaaE+360gHG1+G8VuIykOd9 jyNuFvC/KBP71dAxZ1BydGORB48RMw== =hTvO -----END PGP SIGNATURE----- --5Hiz1LoLsUsCyIomCkUSXPgE8nLr9Rg1d--