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Date: Wed, 15 Jan 2020 12:34:55 +0100 From: Jan Kara <jack@...e.cz> To: Ira Weiny <ira.weiny@...el.com> Cc: "Darrick J. Wong" <darrick.wong@...cle.com>, linux-kernel@...r.kernel.org, Alexander Viro <viro@...iv.linux.org.uk>, Dan Williams <dan.j.williams@...el.com>, Dave Chinner <david@...morbit.com>, Christoph Hellwig <hch@....de>, "Theodore Y. Ts'o" <tytso@....edu>, Jan Kara <jack@...e.cz>, linux-ext4@...r.kernel.org, linux-xfs@...r.kernel.org, linux-fsdevel@...r.kernel.org Subject: Re: [RFC PATCH V2 09/12] fs: Prevent mode change if file is mmap'ed On Tue 14-01-20 09:53:54, Ira Weiny wrote: > On Mon, Jan 13, 2020 at 05:30:04PM -0800, Darrick J. Wong wrote: > > > > > + error = -EBUSY; > > > > > + goto out_unlock; > > > > > + } > > > > > + > > > > > error = filemap_write_and_wait(inode->i_mapping); > > > > > if (error) > > > > > goto out_unlock; > > > > > diff --git a/include/linux/fs.h b/include/linux/fs.h > > > > > index 631f11d6246e..6e7dc626b657 100644 > > > > > --- a/include/linux/fs.h > > > > > +++ b/include/linux/fs.h > > > > > @@ -740,6 +740,7 @@ struct inode { > > > > > #endif > > > > > > > > > > void *i_private; /* fs or device private pointer */ > > > > > + atomic64_t i_mapped; > > > > > > > > I would have expected to find this in struct address_space since the > > > > mapping count is a function of the address space, right? > > > > > > I suppose but the only external call (above) would be passing an inode. So to > > > me it seemed better here. > > > > But the number of memory mappings reflects the state of the address > > space, not the inode. Or maybe put another way, if I were an mm > > developer I would not expect to look in struct inode for mm state. > > This is a good point... > > > > > static inline bool inode_has_mappings(struct inode *inode) > > { > > return atomic64_read(&inode->i_mapping->mapcount) > 0; > > } > > > > OTOH if there exist other mm developers who /do/ find that storing the > > mmap count in struct inode is more logical, please let me know. :) > > ... My thinking was that the number of mappings does not matters to the mm > system... However, I'm starting to think you are correct... ;-) > > I've made a note of it and we will see what others think. Well, more importantly mapping != inode. There can be multiple inodes pointing to the same mapping (struct address_space) as is the case for example for block devices. So this counter definitely belongs into struct address_space. Honza -- Jan Kara <jack@...e.com> SUSE Labs, CR
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