From 61d0017e5a32d3b13ba3c7becc83a5a9e53cdbe9 Mon Sep 17 00:00:00 2001 From: Jens Axboe Date: Fri, 5 Nov 2021 13:37:07 -0700 Subject: [PATCH] mm: don't read i_size of inode unless we need it We always go through i_size_read(), and we rarely end up needing it. Push the read to down where we need to check it, which avoids it for most cases. It looks like we can even remove this check entirely, which might be worth pursuing. But at least this takes it out of the hot path. Link: https://lkml.kernel.org/r/6b67981f-57d4-c80e-bc07-6020aa601381@kernel.dk Signed-off-by: Jens Axboe Acked-by: Chris Mason Cc: Josef Bacik Cc: Dave Chinner Cc: Pavel Begunkov Cc: Jan Kara Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/filemap.c | 7 +++---- 1 file changed, 3 insertions(+), 4 deletions(-) diff --git a/mm/filemap.c b/mm/filemap.c index e50be51..ebd6889 100644 --- a/mm/filemap.c +++ b/mm/filemap.c @@ -2740,9 +2740,7 @@ generic_file_read_iter(struct kiocb *iocb, struct iov_iter *iter) struct file *file = iocb->ki_filp; struct address_space *mapping = file->f_mapping; struct inode *inode = mapping->host; - loff_t size; - size = i_size_read(inode); if (iocb->ki_flags & IOCB_NOWAIT) { if (filemap_range_needs_writeback(mapping, iocb->ki_pos, iocb->ki_pos + count - 1)) @@ -2774,8 +2772,9 @@ generic_file_read_iter(struct kiocb *iocb, struct iov_iter *iter) * the rest of the read. Buffered reads will not work for * DAX files, so don't bother trying. */ - if (retval < 0 || !count || iocb->ki_pos >= size || - IS_DAX(inode)) + if (retval < 0 || !count || IS_DAX(inode)) + return retval; + if (iocb->ki_pos >= i_size_read(inode)) return retval; } -- 2.7.4