On Wed, Oct 20, 2021 at 11:10:31AM +0100, David Howells wrote: > Under some circumstances, filemap_read() will allocate sufficient pages to > read to the end of the file, call readahead/readpages on them and copy the > data over - and then it will allocate another page at the EOF and call > readpage on that and then ignore it. This is unnecessary and a waste of > time and resources. > > filemap_read() *does* check for this, but only after it has already done > the allocation and I/O. Fix this by checking before calling > filemap_get_pages() also. > > Changes: > v2) Break out of the loop immediately rather than going to put_pages (the > pvec is unoccupied). Setting isize is then unnecessary. > > Signed-off-by: David Howells <dhowells@xxxxxxxxxx> > cc: Kent Overstreet <kent.overstreet@xxxxxxxxx> > cc: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx> > cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> > cc: Jeff Layton <jlayton@xxxxxxxxxx> > cc: linux-mm@xxxxxxxxx > cc: linux-fsdevel@xxxxxxxxxxxxxxx > Link: https://lore.kernel.org/r/160588481358.3465195.16552616179674485179.stgit@xxxxxxxxxxxxxxxxxxxxxx/ > Link: https://lore.kernel.org/r/163456863216.2614702.6384850026368833133.stgit@xxxxxxxxxxxxxxxxxxxxxx/ Reviewed-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx>
