On Thu, Aug 13, 2020 at 04:11:22PM +0800, Zhaoyang Huang wrote: > file->f_ra->ra_pages will remain the initialized value since it opend, which > may > be NOT equal to bdi->ra_pages as the latter one is updated somehow(etc, > echo xxx > /sys/block/dm/queue/read_ahead_kb).So having readahead use > bdi->ra_pages.
But now it ignores the work done by shrink_readahead_size_eio() and fadvise(POSIX_FADV_SEQUENTIAL). And you missed the use of ra_size on the previous line, miscalculating ra->start. > Signed-off-by: Zhaoyang Huang <[email protected]> > --- > mm/filemap.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/mm/filemap.c b/mm/filemap.c > index d78f577..259dcfd 100644 > --- a/mm/filemap.c > +++ b/mm/filemap.c > @@ -2499,8 +2499,8 @@ static struct file *do_sync_mmap_readahead(struct > vm_fault *vmf) > */ > fpin = maybe_unlock_mmap_for_io(vmf, fpin); > ra->start = max_t(long, 0, offset - ra->ra_pages / 2); > - ra->size = ra->ra_pages; > - ra->async_size = ra->ra_pages / 4; > + ra->size = inode_to_bdi(mapping->host)->ra_pages; > + ra->async_size = ra->size / 4; > ra_submit(ra, mapping, file); > return fpin; > } > -- > 1.9.1 > >
