sync on pages containing EOF

[Rajagopal Ananthanarayanan <ananth@sgi.com>]

I was looking at some code to deal with sync (eg. sys_fsync(fd)).
Generally, sync is performed by calling filemap_fdatasync(...)
which does writepage() on pages in the dirty list of the inode,
and then using filemap_fdatawait to wait on the I/O's started by
the writepage's.

Consider writepage() on a (partial) page containing EOF. In this case,
prepare_write/commit_write is employed to write the page out.
However, commit_write will only mark the buffer dirty, and
not actually start the I/O. Subsequently, either memory pressure
(page_launder) or write pressure (flush_dirty_buffers) will
start the I/O on the EOF-page. So, it appears that filemap_fdatawait
will be delayed.

I'm just wondering if this argument is correct ...

-- 
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Rajagopal Ananthanarayanan ("ananth")
Member Technical Staff, SGI.
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