Re: Access to non-RAM pages

[Linus Torvalds]

On Sun, Sep 2, 2018 at 7:47 PM Linus Torvalds
<torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
>
> The comment actually does talk about it, although the comment also
> claims that the cs read would use load_unaligned_zeropad(), which it
> no longer does (now it only does the read_word_at_a_time).

IOW, look at commit 12f8ad4b0533 ("vfs: clean up __d_lookup_rcu() and
dentry_cmp() interfaces") for why the zeropad went away for the cs
access (but the comment wasn't updated).

And then bfe7aa6c39b1 ("fs/dcache: Use read_word_at_a_time() in
dentry_string_cmp()") did the "let's make KASAN happy thing.

And yes, the word-at-a-time code actually matters a lot for certain
loads. The "copy-and-hash" thing for path components ends up being
pretty critical in all the pathname handling.

            Linus