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_HELO_NONE,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 DA707C04AB6 for ; Fri, 31 May 2019 08:29:38 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id A9D44265C6 for ; Fri, 31 May 2019 08:29:38 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726403AbfEaI3h (ORCPT ); Fri, 31 May 2019 04:29:37 -0400 Received: from mx2.suse.de ([195.135.220.15]:51482 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1725963AbfEaI3h (ORCPT ); Fri, 31 May 2019 04:29:37 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 6FFB5AB5F for ; Fri, 31 May 2019 08:29:35 +0000 (UTC) Subject: Re: [PATCH 1/3] btrfs: switch extent_buffer blocking_writers from atomic to int To: David Sterba , linux-btrfs@vger.kernel.org References: From: Nikolay Borisov Openpgp: preference=signencrypt Autocrypt: addr=nborisov@suse.com; prefer-encrypt=mutual; keydata= mQINBFiKBz4BEADNHZmqwhuN6EAzXj9SpPpH/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/ogKPk4ZxOXQEZetkEyTFghbRH2BIwARAQABtCNOaWtvbGF5IEJv cmlzb3YgPG5ib3Jpc292QHN1c2UuY29tPokCOAQTAQIAIgUCWIo48QIbAwYLCQgHAwIGFQgC CQoLBBYCAwECHgECF4AACgkQcb6CRuU/KFc0eg/9GLD3wTQz9iZHMFbjiqTCitD7B6dTLV1C ddZVlC8Hm/TophPts1bWZORAmYIihHHI1EIF19+bfIr46pvfTu0yFrJDLOADMDH+Ufzsfy2v HSqqWV/nOSWGXzh8bgg/ncLwrIdEwBQBN9SDS6aqsglagvwFD91UCg/TshLlRxD5BOnuzfzI Leyx2c6YmH7Oa1R4MX9Jo79SaKwdHt2yRN3SochVtxCyafDlZsE/efp21pMiaK1HoCOZTBp5 VzrIP85GATh18pN7YR9CuPxxN0V6IzT7IlhS4Jgj0NXh6vi1DlmKspr+FOevu4RVXqqcNTSS E2rycB2v6cttH21UUdu/0FtMBKh+rv8+yD49FxMYnTi1jwVzr208vDdRU2v7Ij/TxYt/v4O8 V+jNRKy5Fevca/1xroQBICXsNoFLr10X5IjmhAhqIH8Atpz/89ItS3+HWuE4BHB6RRLM0gy8 T7rN6ja+KegOGikp/VTwBlszhvfLhyoyjXI44Tf3oLSFM+8+qG3B7MNBHOt60CQlMkq0fGXd mm4xENl/SSeHsiomdveeq7cNGpHi6i6ntZK33XJLwvyf00PD7tip/GUj0Dic/ZUsoPSTF/mG EpuQiUZs8X2xjK/AS/l3wa4Kz2tlcOKSKpIpna7V1+CMNkNzaCOlbv7QwprAerKYywPCoOSC 7P25Ag0EWIoHPgEQAMiUqvRBZNvPvki34O/dcTodvLSyOmK/MMBDrzN8Cnk302XfnGlW/YAQ csMWISKKSpStc6tmD+2Y0z9WjyRqFr3EGfH1RXSv9Z1vmfPzU42jsdZn667UxrRcVQXUgoKg QYx055Q2FdUeaZSaivoIBD9WtJq/66UPXRRr4H/+Y5FaUZx+gWNGmBT6a0S/GQnHb9g3nonD jmDKGw+YO4P6aEMxyy3k9PstaoiyBXnzQASzdOi39BgWQuZfIQjN0aW+Dm8kOAfT5i/yk59h VV6v3NLHBjHVw9kHli3jwvsizIX9X2W8tb1SefaVxqvqO1132AO8V9CbE1DcVT8fzICvGi42 FoV/k0QOGwq+LmLf0t04Q0csEl+h69ZcqeBSQcIMm/Ir+NorfCr6HjrB6lW7giBkQl6hhomn l1mtDP6MTdbyYzEiBFcwQD4terc7S/8ELRRybWQHQp7sxQM/Lnuhs77MgY/e6c5AVWnMKd/z MKm4ru7A8+8gdHeydrRQSWDaVbfy3Hup0Ia76J9FaolnjB8YLUOJPdhI2vbvNCQ2ipxw3Y3c KhVIpGYqwdvFIiz0Fej7wnJICIrpJs/+XLQHyqcmERn3s/iWwBpeogrx2Lf8AGezqnv9woq7 OSoWlwXDJiUdaqPEB/HmGfqoRRN20jx+OOvuaBMPAPb+aKJyle8zABEBAAGJAh8EGAECAAkF AliKBz4CGwwACgkQcb6CRuU/KFdacg/+M3V3Ti9JYZEiIyVhqs+yHb6NMI1R0kkAmzsGQ1jU zSQUz9AVMR6T7v2fIETTT/f5Oout0+Hi9cY8uLpk8CWno9V9eR/B7Ifs2pAA8lh2nW43FFwp IDiSuDbH6oTLmiGCB206IvSuaQCp1fed8U6yuqGFcnf0ZpJm/sILG2ECdFK9RYnMIaeqlNQm iZicBY2lmlYFBEaMXHoy+K7nbOuizPWdUKoKHq+tmZ3iA+qL5s6Qlm4trH28/fPpFuOmgP8P K+7LpYLNSl1oQUr+WlqilPAuLcCo5Vdl7M7VFLMq4xxY/dY99aZx0ZJQYFx0w/6UkbDdFLzN upT7NIN68lZRucImffiWyN7CjH23X3Tni8bS9ubo7OON68NbPz1YIaYaHmnVQCjDyDXkQoKC R82Vf9mf5slj0Vlpf+/Wpsv/TH8X32ajva37oEQTkWNMsDxyw3aPSps6MaMafcN7k60y2Wk/ TCiLsRHFfMHFY6/lq/c0ZdOsGjgpIK0G0z6et9YU6MaPuKwNY4kBdjPNBwHreucrQVUdqRRm RcxmGC6ohvpqVGfhT48ZPZKZEWM+tZky0mO7bhZYxMXyVjBn4EoNTsXy1et9Y1dU3HVJ8fod 5UqrNrzIQFbdeM0/JqSLrtlTcXKJ7cYFa9ZM2AP7UIN9n1UWxq+OPY9YMOewVfYtL8M= Message-ID: Date: Fri, 31 May 2019 11:29:33 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.6.1 MIME-Version: 1.0 In-Reply-To: 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 30.05.19 г. 19:31 ч., David Sterba wrote: > The blocking_writers is either 0 or 1 and always updated under the lock, > so we don't need the atomic_t semantics.> > Signed-off-by: David Sterba Reviewed-by: Nikolay Borisov > --- > fs/btrfs/extent_io.c | 2 +- > fs/btrfs/extent_io.h | 2 +- > fs/btrfs/locking.c | 46 +++++++++++++++++++------------------------ > fs/btrfs/print-tree.c | 2 +- > 4 files changed, 23 insertions(+), 29 deletions(-) > > diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c > index 2f38c10d2bfb..57b6de9df7c4 100644 > --- a/fs/btrfs/extent_io.c > +++ b/fs/btrfs/extent_io.c > @@ -4823,7 +4823,7 @@ __alloc_extent_buffer(struct btrfs_fs_info *fs_info, u64 start, > eb->bflags = 0; > rwlock_init(&eb->lock); > atomic_set(&eb->blocking_readers, 0); > - atomic_set(&eb->blocking_writers, 0); > + eb->blocking_writers = 0; > eb->lock_nested = false; > init_waitqueue_head(&eb->write_lock_wq); > init_waitqueue_head(&eb->read_lock_wq); > diff --git a/fs/btrfs/extent_io.h b/fs/btrfs/extent_io.h > index aa18a16a6ed7..201da61dfc21 100644 > --- a/fs/btrfs/extent_io.h > +++ b/fs/btrfs/extent_io.h > @@ -167,7 +167,7 @@ struct extent_buffer { > struct rcu_head rcu_head; > pid_t lock_owner; > > - atomic_t blocking_writers; > + int blocking_writers; > atomic_t blocking_readers; > bool lock_nested; > /* >= 0 if eb belongs to a log tree, -1 otherwise */ > diff --git a/fs/btrfs/locking.c b/fs/btrfs/locking.c > index 2f6c3c7851ed..5feb01147e19 100644 > --- a/fs/btrfs/locking.c > +++ b/fs/btrfs/locking.c > @@ -111,10 +111,10 @@ void btrfs_set_lock_blocking_write(struct extent_buffer *eb) > */ > if (eb->lock_nested && current->pid == eb->lock_owner) > return; > - if (atomic_read(&eb->blocking_writers) == 0) { > + if (eb->blocking_writers == 0) { > btrfs_assert_spinning_writers_put(eb); > btrfs_assert_tree_locked(eb); > - atomic_inc(&eb->blocking_writers); > + eb->blocking_writers++; > write_unlock(&eb->lock); > } > } > @@ -148,12 +148,11 @@ void btrfs_clear_lock_blocking_write(struct extent_buffer *eb) > */ > if (eb->lock_nested && current->pid == eb->lock_owner) > return; > - BUG_ON(atomic_read(&eb->blocking_writers) != 1); > write_lock(&eb->lock); > + BUG_ON(eb->blocking_writers != 1); > btrfs_assert_spinning_writers_get(eb); > - /* atomic_dec_and_test implies a barrier */ > - if (atomic_dec_and_test(&eb->blocking_writers)) > - cond_wake_up_nomb(&eb->write_lock_wq); > + if (--eb->blocking_writers == 0) > + cond_wake_up(&eb->write_lock_wq); > } > > /* > @@ -167,12 +166,10 @@ void btrfs_tree_read_lock(struct extent_buffer *eb) > if (trace_btrfs_tree_read_lock_enabled()) > start_ns = ktime_get_ns(); > again: > - BUG_ON(!atomic_read(&eb->blocking_writers) && > - current->pid == eb->lock_owner); > - > read_lock(&eb->lock); > - if (atomic_read(&eb->blocking_writers) && > - current->pid == eb->lock_owner) { > + BUG_ON(eb->blocking_writers == 0 && > + current->pid == eb->lock_owner); > + if (eb->blocking_writers && current->pid == eb->lock_owner) { > /* > * This extent is already write-locked by our thread. We allow > * an additional read lock to be added because it's for the same > @@ -185,10 +182,10 @@ void btrfs_tree_read_lock(struct extent_buffer *eb) > trace_btrfs_tree_read_lock(eb, start_ns); > return; > } > - if (atomic_read(&eb->blocking_writers)) { > + if (eb->blocking_writers) { > read_unlock(&eb->lock); > wait_event(eb->write_lock_wq, > - atomic_read(&eb->blocking_writers) == 0); > + eb->blocking_writers == 0); > goto again; > } > btrfs_assert_tree_read_locks_get(eb); > @@ -203,11 +200,11 @@ void btrfs_tree_read_lock(struct extent_buffer *eb) > */ > int btrfs_tree_read_lock_atomic(struct extent_buffer *eb) > { > - if (atomic_read(&eb->blocking_writers)) > + if (eb->blocking_writers) > return 0; > > read_lock(&eb->lock); > - if (atomic_read(&eb->blocking_writers)) { > + if (eb->blocking_writers) { > read_unlock(&eb->lock); > return 0; > } > @@ -223,13 +220,13 @@ int btrfs_tree_read_lock_atomic(struct extent_buffer *eb) > */ > int btrfs_try_tree_read_lock(struct extent_buffer *eb) > { > - if (atomic_read(&eb->blocking_writers)) > + if (eb->blocking_writers) > return 0; > > if (!read_trylock(&eb->lock)) > return 0; > > - if (atomic_read(&eb->blocking_writers)) { > + if (eb->blocking_writers) { > read_unlock(&eb->lock); > return 0; > } > @@ -245,13 +242,11 @@ int btrfs_try_tree_read_lock(struct extent_buffer *eb) > */ > int btrfs_try_tree_write_lock(struct extent_buffer *eb) > { > - if (atomic_read(&eb->blocking_writers) || > - atomic_read(&eb->blocking_readers)) > + if (eb->blocking_writers || atomic_read(&eb->blocking_readers)) > return 0; > > write_lock(&eb->lock); > - if (atomic_read(&eb->blocking_writers) || > - atomic_read(&eb->blocking_readers)) { > + if (eb->blocking_writers || atomic_read(&eb->blocking_readers)) { > write_unlock(&eb->lock); > return 0; > } > @@ -322,10 +317,9 @@ void btrfs_tree_lock(struct extent_buffer *eb) > WARN_ON(eb->lock_owner == current->pid); > again: > wait_event(eb->read_lock_wq, atomic_read(&eb->blocking_readers) == 0); > - wait_event(eb->write_lock_wq, atomic_read(&eb->blocking_writers) == 0); > + wait_event(eb->write_lock_wq, eb->blocking_writers == 0); > write_lock(&eb->lock); > - if (atomic_read(&eb->blocking_readers) || > - atomic_read(&eb->blocking_writers)) { > + if (atomic_read(&eb->blocking_readers) || eb->blocking_writers) { > write_unlock(&eb->lock); > goto again; > } > @@ -340,7 +334,7 @@ void btrfs_tree_lock(struct extent_buffer *eb) > */ > void btrfs_tree_unlock(struct extent_buffer *eb) > { > - int blockers = atomic_read(&eb->blocking_writers); > + int blockers = eb->blocking_writers; > > BUG_ON(blockers > 1); > > @@ -351,7 +345,7 @@ void btrfs_tree_unlock(struct extent_buffer *eb) > > if (blockers) { > btrfs_assert_no_spinning_writers(eb); > - atomic_dec(&eb->blocking_writers); > + eb->blocking_writers--; > /* Use the lighter barrier after atomic */ > smp_mb__after_atomic(); > cond_wake_up_nomb(&eb->write_lock_wq); > diff --git a/fs/btrfs/print-tree.c b/fs/btrfs/print-tree.c > index 1141ca5fae6a..7cb4f1fbe043 100644 > --- a/fs/btrfs/print-tree.c > +++ b/fs/btrfs/print-tree.c > @@ -155,7 +155,7 @@ static void print_eb_refs_lock(struct extent_buffer *eb) > "refs %u lock (w:%d r:%d bw:%d br:%d sw:%d sr:%d) lock_owner %u current %u", > atomic_read(&eb->refs), atomic_read(&eb->write_locks), > atomic_read(&eb->read_locks), > - atomic_read(&eb->blocking_writers), > + eb->blocking_writers, > atomic_read(&eb->blocking_readers), > atomic_read(&eb->spinning_writers), > atomic_read(&eb->spinning_readers), >