From: Christoph Hellwig <hch@infradead.org>
To: Goldwyn Rodrigues <rgoldwyn@suse.de>
Cc: Christoph Hellwig <hch@infradead.org>,
linux-btrfs@vger.kernel.org, darrick.wong@oracle.com,
fdmanana@kernel.org, nborisov@suse.com, dsterba@suse.cz,
jthumshirn@suse.de, linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH 4/8] btrfs: Switch to iomap_dio_rw() for dio
Date: Tue, 7 Jan 2020 09:23:00 -0800 [thread overview]
Message-ID: <20200107172300.GB11624@infradead.org> (raw)
In-Reply-To: <20200102180127.65oh2zmclpmy75ix@fiona>
On Thu, Jan 02, 2020 at 12:01:27PM -0600, Goldwyn Rodrigues wrote:
> On 6:42 21/12, Christoph Hellwig wrote:
> > So Ilooked into the "unlocked" direct I/O case, and I think the current
> > code using dio_sem is really sketchy. What btrfs really needs to do is
> > take i_rwsem shared by default for direct writes, and only upgrade to
> > the exclusive lock when needed, similar to xfs and the WIP ext4 code.
>
> Sketchy in what sense? I am not trying to second-guess, but I want to
> know where it could fail. I would want it to be simpler as well, but if
> we can perform direct writes without locking, why should we introduce
> locks.
In that it needs yet another lock which doesn't really provide
exclusion guarantees in its own. In many ways this lock plus the
historic i_mutex were abused to provide the shared/exclusiv lock
that now exists natively with i_rwsem.
next prev parent reply other threads:[~2020-01-07 17:23 UTC|newest]
Thread overview: 37+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-12-13 19:57 [PATCH 0/8 v6] btrfs direct-io using iomap Goldwyn Rodrigues
2019-12-13 19:57 ` [PATCH 1/8] fs: Export generic_file_buffered_read() Goldwyn Rodrigues
2019-12-13 19:57 ` [PATCH 2/8] iomap: add a filesystem hook for direct I/O bio submission Goldwyn Rodrigues
2019-12-14 0:31 ` Darrick J. Wong
2019-12-18 2:02 ` Darrick J. Wong
2019-12-13 19:57 ` [PATCH 3/8] iomap: Move lockdep_assert_held() to iomap_dio_rw() calls Goldwyn Rodrigues
2019-12-14 0:32 ` Darrick J. Wong
2019-12-18 2:04 ` Darrick J. Wong
2019-12-21 13:41 ` Christoph Hellwig
2019-12-21 13:42 ` Christoph Hellwig
2019-12-21 18:02 ` Darrick J. Wong
2019-12-13 19:57 ` [PATCH 4/8] btrfs: Switch to iomap_dio_rw() for dio Goldwyn Rodrigues
2019-12-21 14:42 ` Christoph Hellwig
2020-01-02 18:01 ` Goldwyn Rodrigues
2020-01-07 17:23 ` Christoph Hellwig [this message]
2020-01-07 11:59 ` Goldwyn Rodrigues
2020-01-07 17:21 ` Christoph Hellwig
2019-12-13 19:57 ` [PATCH 5/8] fs: Remove dio_end_io() Goldwyn Rodrigues
2019-12-13 19:57 ` [PATCH 6/8] btrfs: Wait for extent bits to release page Goldwyn Rodrigues
2019-12-13 19:57 ` [PATCH 7/8] btrfs: Use ->iomap_end() instead of btrfs_dio_data Goldwyn Rodrigues
2019-12-13 19:57 ` [PATCH 8/8] btrfs: remove BTRFS_INODE_READDIO_NEED_LOCK Goldwyn Rodrigues
2019-12-16 0:01 ` [PATCH 0/8 v6] btrfs direct-io using iomap Nikolay Borisov
2019-12-16 12:41 ` Goldwyn Rodrigues
-- strict thread matches above, loose matches on Subject: below --
2019-12-10 23:01 [PATCH 0/8 v4] " Goldwyn Rodrigues
2019-12-10 23:01 ` [PATCH 4/8] btrfs: Switch to iomap_dio_rw() for dio Goldwyn Rodrigues
2019-12-11 8:58 ` Filipe Manana
2019-12-11 10:43 ` Nikolay Borisov
2019-12-05 15:56 [PATCH 0/8 v3] btrfs direct-io using iomap Goldwyn Rodrigues
2019-12-05 15:56 ` [PATCH 4/8] btrfs: Switch to iomap_dio_rw() for dio Goldwyn Rodrigues
2019-12-05 17:18 ` Johannes Thumshirn
2019-12-05 17:19 ` Christoph Hellwig
2019-12-05 17:32 ` Johannes Thumshirn
2019-12-05 17:33 ` Christoph Hellwig
2019-12-05 17:36 ` Johannes Thumshirn
2019-12-05 17:37 ` Christoph Hellwig
2019-12-05 17:37 ` Christoph Hellwig
2019-12-05 17:40 ` Johannes Thumshirn
2019-12-05 17:44 ` Goldwyn Rodrigues
2019-12-05 22:59 ` Nikolay Borisov
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