From: David Howells <dhowells@xxxxxxxxxx> Subject: mm: stop filemap_read() from grabbing a superfluous page 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. Link: https://lkml.kernel.org/r/163472463105.3126792.7056099385135786492.stgit@xxxxxxxxxxxxxxxxxxxxxx Link: https://lore.kernel.org/r/160588481358.3465195.16552616179674485179.stgit@xxxxxxxxxxxxxxxxxxxxxx/ Link: https://lore.kernel.org/r/163456863216.2614702.6384850026368833133.stgit@xxxxxxxxxxxxxxxxxxxxxx/ Signed-off-by: David Howells <dhowells@xxxxxxxxxx> Acked-by: Jeff Layton <jlayton@xxxxxxxxxx> Reviewed-by: Matthew Wilcox (Oracle) <willy@xxxxxxxxxxxxx> Cc: Kent Overstreet <kent.overstreet@xxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- mm/filemap.c | 3 +++ 1 file changed, 3 insertions(+) --- a/mm/filemap.c~mm-stop-filemap_read-from-grabbing-a-superfluous-page +++ a/mm/filemap.c @@ -2625,6 +2625,9 @@ ssize_t filemap_read(struct kiocb *iocb, 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; _
