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=-7.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS,URIBL_BLOCKED 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 A17F3C43441 for ; Fri, 23 Nov 2018 13:50:52 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 5AE9A206B2 for ; Fri, 23 Nov 2018 13:50:52 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 5AE9A206B2 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=suse.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-btrfs-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2436542AbeKXAfH (ORCPT ); Fri, 23 Nov 2018 19:35:07 -0500 Received: from mx2.suse.de ([195.135.220.15]:45536 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S2388620AbeKXAfG (ORCPT ); Fri, 23 Nov 2018 19:35:06 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay1.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 7EE7EAF97; Fri, 23 Nov 2018 13:50:47 +0000 (UTC) Subject: Re: [PATCH 1/6] btrfs: add btrfs_delete_ref_head helper To: dsterba@suse.cz, Josef Bacik , linux-btrfs@vger.kernel.org, kernel-team@fb.com, Josef Bacik References: <20181121185912.24288-1-josef@toxicpanda.com> <20181121185912.24288-2-josef@toxicpanda.com> <9e2495bc-4bcc-046c-2416-415a7e48c681@suse.com> <3eb452b8-d07f-530e-a16e-8d8fd5938b87@suse.com> <20181123134525.GC2842@twin.jikos.cz> From: Nikolay Borisov Openpgp: preference=signencrypt Autocrypt: addr=nborisov@suse.com; prefer-encrypt=mutual; keydata= xsFNBFiKBz4BEADNHZmqwhuN6EAzXj9SpPpH/nSSP8YgfwoOqwrP+JR4pIqRK0AWWeWCSwmZ T7g+RbfPFlmQp+EwFWOtABXlKC54zgSf+uulGwx5JAUFVUIRBmnHOYi/lUiE0yhpnb1KCA7f u/W+DkwGerXqhhe9TvQoGwgCKNfzFPZoM+gZrm+kWv03QLUCr210n4cwaCPJ0Nr9Z3c582xc bCUVbsjt7BN0CFa2BByulrx5xD9sDAYIqfLCcZetAqsTRGxM7LD0kh5WlKzOeAXj5r8DOrU2 GdZS33uKZI/kZJZVytSmZpswDsKhnGzRN1BANGP8sC+WD4eRXajOmNh2HL4P+meO1TlM3GLl EQd2shHFY0qjEo7wxKZI1RyZZ5AgJnSmehrPCyuIyVY210CbMaIKHUIsTqRgY5GaNME24w7h TyyVCy2qAM8fLJ4Vw5bycM/u5xfWm7gyTb9V1TkZ3o1MTrEsrcqFiRrBY94Rs0oQkZvunqia c+NprYSaOG1Cta14o94eMH271Kka/reEwSZkC7T+o9hZ4zi2CcLcY0DXj0qdId7vUKSJjEep c++s8ncFekh1MPhkOgNj8pk17OAESanmDwksmzh1j12lgA5lTFPrJeRNu6/isC2zyZhTwMWs k3LkcTa8ZXxh0RfWAqgx/ogKPk4ZxOXQEZetkEyTFghbRH2BIwARAQABzSJOaWtvbGF5IEJv cmlzb3YgPG5ib3Jpc292QHN1c2UuZGU+wsF4BBMBAgAiBQJYijkSAhsDBgsJCAcDAgYVCAIJ CgsEFgIDAQIeAQIXgAAKCRBxvoJG5T8oV/B6D/9a8EcRPdHg8uLEPywuJR8URwXzkofT5bZE IfGF0Z+Lt2ADe+nLOXrwKsamhweUFAvwEUxxnndovRLPOpWerTOAl47lxad08080jXnGfYFS Dc+ew7C3SFI4tFFHln8Y22Q9075saZ2yQS1ywJy+TFPADIprAZXnPbbbNbGtJLoq0LTiESnD w/SUC6sfikYwGRS94Dc9qO4nWyEvBK3Ql8NkoY0Sjky3B0vL572Gq0ytILDDGYuZVo4alUs8 LeXS5ukoZIw1QYXVstDJQnYjFxYgoQ5uGVi4t7FsFM/6ykYDzbIPNOx49Rbh9W4uKsLVhTzG BDTzdvX4ARl9La2kCQIjjWRg+XGuBM5rxT/NaTS78PXjhqWNYlGc5OhO0l8e5DIS2tXwYMDY LuHYNkkpMFksBslldvNttSNei7xr5VwjVqW4vASk2Aak5AleXZS+xIq2FADPS/XSgIaepyTV tkfnyreep1pk09cjfXY4A7qpEFwazCRZg9LLvYVc2M2eFQHDMtXsH59nOMstXx2OtNMcx5p8 0a5FHXE/HoXz3p9bD0uIUq6p04VYOHsMasHqHPbsMAq9V2OCytJQPWwe46bBjYZCOwG0+x58 fBFreP/NiJNeTQPOa6FoxLOLXMuVtpbcXIqKQDoEte9aMpoj9L24f60G4q+pL/54ql2VRscK d87BTQRYigc+ARAAyJSq9EFk28++SLfg791xOh28tLI6Yr8wwEOvM3wKeTfTZd+caVb9gBBy wxYhIopKlK1zq2YP7ZjTP1aPJGoWvcQZ8fVFdK/1nW+Z8/NTjaOx1mfrrtTGtFxVBdSCgqBB jHTnlDYV1R5plJqK+ggEP1a0mr/rpQ9dFGvgf/5jkVpRnH6BY0aYFPprRL8ZCcdv2DeeicOO YMobD5g7g/poQzHLLeT0+y1qiLIFefNABLN06Lf0GBZC5l8hCM3Rpb4ObyQ4B9PmL/KTn2FV Xq/c0scGMdXD2QeWLePC+yLMhf1fZby1vVJ59pXGq+o7XXfYA7xX0JsTUNxVPx/MgK8aLjYW hX+TRA4bCr4uYt/S3ThDRywSX6Hr1lyp4FJBwgyb8iv42it8KvoeOsHqVbuCIGRCXqGGiaeX Wa0M/oxN1vJjMSIEVzBAPi16tztL/wQtFHJtZAdCnuzFAz8ue6GzvsyBj97pzkBVacwp3/Mw qbiu7sDz7yB0d7J2tFBJYNpVt/Lce6nQhrvon0VqiWeMHxgtQ4k92Eja9u80JDaKnHDdjdwq FUikZirB28UiLPQV6PvCckgIiukmz/5ctAfKpyYRGfez+JbAGl6iCvHYt/wAZ7Oqe/3Cirs5 KhaXBcMmJR1qo8QH8eYZ+qhFE3bSPH446+5oEw8A9v5oonKV7zMAEQEAAcLBXwQYAQIACQUC WIoHPgIbDAAKCRBxvoJG5T8oV1pyD/4zdXdOL0lhkSIjJWGqz7Idvo0wjVHSSQCbOwZDWNTN JBTP0BUxHpPu/Z8gRNNP9/k6i63T4eL1xjy4umTwJaej1X15H8Hsh+zakADyWHadbjcUXCkg OJK4NsfqhMuaIYIHbToi9K5pAKnV953xTrK6oYVyd/Rmkmb+wgsbYQJ0Ur1Ficwhp6qU1CaJ mJwFjaWaVgUERoxcejL4ruds66LM9Z1Qqgoer62ZneID6ovmzpCWbi2sfbz98+kW46aA/w8r 7sulgs1KXWhBSv5aWqKU8C4twKjlV2XsztUUsyrjHFj91j31pnHRklBgXHTD/pSRsN0UvM26 lPs0g3ryVlG5wiZ9+JbI3sKMfbdfdOeLxtL25ujs443rw1s/PVghphoeadVAKMPINeRCgoJH zZV/2Z/myWPRWWl/79amy/9MfxffZqO9rfugRBORY0ywPHLDdo9Kmzoxoxp9w3uTrTLZaT9M KIuxEcV8wcVjr+Wr9zRl06waOCkgrQbTPp631hToxo+4rA1jiQF2M80HAet65ytBVR2pFGZF zGYYLqiG+mpUZ+FPjxk9kpkRYz61mTLSY7tuFljExfJWMGfgSg1OxfLV631jV1TcdUnx+h3l Sqs2vMhAVt14zT8mpIuu2VNxcontxgVr1kzYA/tQg32fVRbGr449j1gw57BV9i0vww== Message-ID: <1b29b7a7-ab71-4c33-dbdd-077fd92342f4@suse.com> Date: Fri, 23 Nov 2018 15:50:45 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.2.1 MIME-Version: 1.0 In-Reply-To: <20181123134525.GC2842@twin.jikos.cz> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-btrfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-btrfs@vger.kernel.org On 23.11.18 г. 15:45 ч., David Sterba wrote: > On Thu, Nov 22, 2018 at 11:42:28AM +0200, Nikolay Borisov wrote: >> >> >> On 22.11.18 г. 11:12 ч., Nikolay Borisov wrote: >>> >>> >>> On 21.11.18 г. 20:59 ч., Josef Bacik wrote: >>>> From: Josef Bacik >>>> >>>> We do this dance in cleanup_ref_head and check_ref_cleanup, unify it >>>> into a helper and cleanup the calling functions. >>>> >>>> Signed-off-by: Josef Bacik >>>> Reviewed-by: Omar Sandoval >>>> --- >>>> fs/btrfs/delayed-ref.c | 14 ++++++++++++++ >>>> fs/btrfs/delayed-ref.h | 3 ++- >>>> fs/btrfs/extent-tree.c | 22 +++------------------- >>>> 3 files changed, 19 insertions(+), 20 deletions(-) >>>> >>>> diff --git a/fs/btrfs/delayed-ref.c b/fs/btrfs/delayed-ref.c >>>> index 9301b3ad9217..b3e4c9fcb664 100644 >>>> --- a/fs/btrfs/delayed-ref.c >>>> +++ b/fs/btrfs/delayed-ref.c >>>> @@ -400,6 +400,20 @@ struct btrfs_delayed_ref_head *btrfs_select_ref_head( >>>> return head; >>>> } >>>> >>>> +void btrfs_delete_ref_head(struct btrfs_delayed_ref_root *delayed_refs, >>>> + struct btrfs_delayed_ref_head *head) >>>> +{ >>>> + lockdep_assert_held(&delayed_refs->lock); >>>> + lockdep_assert_held(&head->lock); >>>> + >>>> + rb_erase_cached(&head->href_node, &delayed_refs->href_root); >>>> + RB_CLEAR_NODE(&head->href_node); >>>> + atomic_dec(&delayed_refs->num_entries); >>>> + delayed_refs->num_heads--; >>>> + if (head->processing == 0) >>>> + delayed_refs->num_heads_ready--; >>> >>> num_heads_ready will never execute in cleanup_ref_head, since >>> processing == 0 only when the ref head is unselected. Perhaps those 2 >>> lines shouldn't be in this function? I find it a bit confusing that if >>> processing is 0 we decrement num_heads_ready in check_ref_cleanup, but >>> in unselect_delayed_ref_head we set it to 0 and increment it. >>> >>>> +} >>>> + >>>> /* >>>> * Helper to insert the ref_node to the tail or merge with tail. >>>> * >>>> diff --git a/fs/btrfs/delayed-ref.h b/fs/btrfs/delayed-ref.h >>>> index 8e20c5cb5404..d2af974f68a1 100644 >>>> --- a/fs/btrfs/delayed-ref.h >>>> +++ b/fs/btrfs/delayed-ref.h >>>> @@ -261,7 +261,8 @@ static inline void btrfs_delayed_ref_unlock(struct btrfs_delayed_ref_head *head) >>>> { >>>> mutex_unlock(&head->mutex); >>>> } >>>> - >>>> +void btrfs_delete_ref_head(struct btrfs_delayed_ref_root *delayed_refs, >>>> + struct btrfs_delayed_ref_head *head); >>>> >>>> struct btrfs_delayed_ref_head *btrfs_select_ref_head( >>>> struct btrfs_delayed_ref_root *delayed_refs); >>>> diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c >>>> index d242a1174e50..c36b3a42f2bb 100644 >>>> --- a/fs/btrfs/extent-tree.c >>>> +++ b/fs/btrfs/extent-tree.c >>>> @@ -2474,12 +2474,9 @@ static int cleanup_ref_head(struct btrfs_trans_handle *trans, >>>> spin_unlock(&delayed_refs->lock); >>>> return 1; >>>> } >>>> - delayed_refs->num_heads--; >>>> - rb_erase_cached(&head->href_node, &delayed_refs->href_root); >>>> - RB_CLEAR_NODE(&head->href_node); >>>> + btrfs_delete_ref_head(delayed_refs, head); >>>> spin_unlock(&head->lock); >>>> spin_unlock(&delayed_refs->lock); >>>> - atomic_dec(&delayed_refs->num_entries); >>>> >>>> trace_run_delayed_ref_head(fs_info, head, 0); >>>> >>>> @@ -6984,22 +6981,9 @@ static noinline int check_ref_cleanup(struct btrfs_trans_handle *trans, >>>> if (!mutex_trylock(&head->mutex)) >>>> goto out; >>>> >>>> - /* >>>> - * at this point we have a head with no other entries. Go >>>> - * ahead and process it. >>>> - */ >>>> - rb_erase_cached(&head->href_node, &delayed_refs->href_root); >>>> - RB_CLEAR_NODE(&head->href_node); >>>> - atomic_dec(&delayed_refs->num_entries); >>>> - >>>> - /* >>>> - * we don't take a ref on the node because we're removing it from the >>>> - * tree, so we just steal the ref the tree was holding. >>>> - */ >>>> - delayed_refs->num_heads--; >>>> - if (head->processing == 0) >>>> - delayed_refs->num_heads_ready--; >>>> + btrfs_delete_ref_head(delayed_refs, head); >>>> head->processing = 0; >> >> On a closer inspection I think here we can do: >> >> ASSERT(head->processing == 0) because at that point we've taken the >> head->lock spinlock which is held during ordinary delayed refs >> processing (in __btrfs_run_delayed_refs) when the head is selected (and >> processing is 1). So head->processing == 0 here I think is a hard >> invariant of the code. The decrement here should pair with the increment >> when the head was initially added to the tree. >> >> In cleanup_ref_head we don't need to ever worry about num_heads_ready >> since it has already been decremented by btrfs_select_ref_head. >> >> As a matter fact this counter is not used anywhere so we might as well >> just remove it. > > The logic does not use it, there's only a WARN_ON in > btrfs_select_ref_head, that's more like a debugging or assertion that > everything is fine. So the question is whether to keep it as a > consistency check (and add comments) or remove it and simplify the code. IMO it should go. A later patch pretty much tracks what this number used to to track - btrfs: only track ref_heads in delayed_ref_updates. Even for consistency I don't see much value brought by num_heads_ready. >