Re: [PATCH 2/2] squashfs: implement readahead

[Hsin-Yi Wang]

On Mon, May 16, 2022 at 8:36 PM Matthew Wilcox <willy@xxxxxxxxxxxxx> wrote:
>
> On Mon, May 16, 2022 at 07:04:08PM +0800, Hsin-Yi Wang wrote:
> > > +       loff_t req_end = readahead_pos(ractl) + readahead_length(ractl);
> > > +       loff_t start = readahead_pos(ractl) &~ mask;
> > > +       size_t len = readahead_length(ractl) + readahead_pos(ractl) - start;
> > > +       struct squashfs_page_actor *actor;
> > > +       unsigned int nr_pages = 0;
> > > +       struct page **pages;
> > > +       u64 block = 0;
> > > +       int bsize, res, i, index;
> > > +       int file_end = i_size_read(inode) >> msblk->block_log;
> > > +       unsigned int max_pages = 1UL << shift;
> > > +
> > > +       readahead_expand(ractl, start, (len | mask) + 1);
> > > +
> > > +       if (readahead_pos(ractl) + readahead_length(ractl) < req_end ||
> > > +           file_end == 0)
> > > +               return;
>
> What's the first half of this condition supposed to be checking for?
> It seems to be checking whether readahead_expand() shrunk the range
> covered by the ractl, but readahead_expand() never does that, so I'm
> confused why you're checking for it.

hi Matthew,

This is to check if readahead_expand() expands as much as it's requested.
I didn't encounter the mismatch so far in my testing. If this check is
not necessary, it can be removed.