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Fri, 31 May 2019 09:19:16 +0000 (UTC) Subject: Re: [PATCH 2/3] btrfs: switch extent_buffer spinning_writers from atomic to int To: David Sterba , linux-btrfs@vger.kernel.org References: <6dfcb89b254ee5016edfa9816fce3487a23b446c.1559233731.git.dsterba@suse.com> 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: <41aca846-afb1-9b83-f442-d791eb929c36@suse.com> Date: Fri, 31 May 2019 12:19:15 +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: <6dfcb89b254ee5016edfa9816fce3487a23b446c.1559233731.git.dsterba@suse.com> 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 spinning_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 > --- > fs/btrfs/extent_io.c | 2 +- > fs/btrfs/extent_io.h | 2 +- > fs/btrfs/locking.c | 10 +++++----- > fs/btrfs/print-tree.c | 2 +- > 4 files changed, 8 insertions(+), 8 deletions(-) > > diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c > index 57b6de9df7c4..71ee9e976307 100644 > --- a/fs/btrfs/extent_io.c > +++ b/fs/btrfs/extent_io.c > @@ -4842,7 +4842,7 @@ __alloc_extent_buffer(struct btrfs_fs_info *fs_info, u64 start, > BUG_ON(len > MAX_INLINE_EXTENT_BUFFER_SIZE); > > #ifdef CONFIG_BTRFS_DEBUG > - atomic_set(&eb->spinning_writers, 0); > + eb->spinning_writers = 0; > atomic_set(&eb->spinning_readers, 0); > atomic_set(&eb->read_locks, 0); > atomic_set(&eb->write_locks, 0); > diff --git a/fs/btrfs/extent_io.h b/fs/btrfs/extent_io.h > index 201da61dfc21..5616b96c365d 100644 > --- a/fs/btrfs/extent_io.h > +++ b/fs/btrfs/extent_io.h > @@ -187,7 +187,7 @@ struct extent_buffer { > wait_queue_head_t read_lock_wq; > struct page *pages[INLINE_EXTENT_BUFFER_PAGES]; > #ifdef CONFIG_BTRFS_DEBUG > - atomic_t spinning_writers; > + int spinning_writers; > atomic_t spinning_readers; > atomic_t read_locks; > atomic_t write_locks; > diff --git a/fs/btrfs/locking.c b/fs/btrfs/locking.c > index 5feb01147e19..270667627977 100644 > --- a/fs/btrfs/locking.c > +++ b/fs/btrfs/locking.c > @@ -15,19 +15,19 @@ > #ifdef CONFIG_BTRFS_DEBUG > static void btrfs_assert_spinning_writers_get(struct extent_buffer *eb) > { > - WARN_ON(atomic_read(&eb->spinning_writers)); > - atomic_inc(&eb->spinning_writers); > + WARN_ON(eb->spinning_writers); > + eb->spinning_writers++; > } > > static void btrfs_assert_spinning_writers_put(struct extent_buffer *eb) > { > - WARN_ON(atomic_read(&eb->spinning_writers) != 1); > - atomic_dec(&eb->spinning_writers); > + WARN_ON(eb->spinning_writers != 1); > + eb->spinning_writers--; > } > > static void btrfs_assert_no_spinning_writers(struct extent_buffer *eb) > { > - WARN_ON(atomic_read(&eb->spinning_writers)); > + WARN_ON(eb->spinning_writers); > } IMO longterm it will be good if those debug functions contained lockdep_assert_held_exclusive/read macros for posterity. > > static void btrfs_assert_spinning_readers_get(struct extent_buffer *eb) > diff --git a/fs/btrfs/print-tree.c b/fs/btrfs/print-tree.c > index 7cb4f1fbe043..c5cc435ed39a 100644 > --- a/fs/btrfs/print-tree.c > +++ b/fs/btrfs/print-tree.c > @@ -157,7 +157,7 @@ static void print_eb_refs_lock(struct extent_buffer *eb) > atomic_read(&eb->read_locks), > eb->blocking_writers, > atomic_read(&eb->blocking_readers), > - atomic_read(&eb->spinning_writers), > + eb->spinning_writers, > atomic_read(&eb->spinning_readers), > eb->lock_owner, current->pid); > #endif >