[pnfs] Getting layout in pnfs_file_read, pnfs_file_write

[William A. (Andy) Adamson]

pnfs_file_read and pnfs_file_write are hit very early in the read/write path

sys_read/write -> vfs_read/write -> pnfs_file_read/write.

Is there a reason for the ordering of tasks in these routines?

------- current pnfs_file_read/write ------

using the page cache? -> do not get a layout, call do_sync_read/write.

else

check if below threashold. But! this check requires a layout.

try to get a layout. if successful, call the layout driver read/write
function.

------------------------

Why not get a layout as early as possible?

------- proposed ------

get a layout

use page cache? call do_sync_read/write

not using page cache?

check below threadhold - if so, call do_sync_read/write
else call layout driver read/write.

--------------------------------

-->Andy
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