On Wed, 2021-10-20 at 11:10 +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/ > --- > > mm/filemap.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/mm/filemap.c b/mm/filemap.c > index dae481293b5d..e50be519f6a4 100644 > --- a/mm/filemap.c > +++ b/mm/filemap.c > @@ -2625,6 +2625,9 @@ ssize_t filemap_read(struct kiocb *iocb, struct iov_iter *iter, > if ((iocb->ki_flags & IOCB_WAITQ) && already_read) > iocb->ki_flags |= IOCB_NOWAIT; > > + if (unlikely(iocb->ki_pos >= i_size_read(inode))) > + break; > + > error = filemap_get_pages(iocb, iter, &pvec); > if (error < 0) > break; > > Even better. Acked-by: Jeff Layton <jlayton@xxxxxxxxxx>
