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From: Linus Torvalds <torvalds@linux-foundation.org>
To: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: "Jiri Kosina" <jikos@kernel.org>, "Jürgen Groß" <jgross@suse.com>,
	"Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>,
	"Michal Hocko" <mhocko@suse.com>,
	"Naoya Horiguchi" <n-horiguchi@ah.jp.nec.com>,
	"Michael Ellerman" <mpe@ellerman.id.au>,
	"Will Deacon" <will.deacon@arm.com>
Subject: Re: Access to non-RAM pages
Date: Sun, 2 Sep 2018 19:52:02 -0700	[thread overview]
Message-ID: <CA+55aFwu8K5=DfVrLBgoDP33m-izCMqZoQ6UogCmYC8kN_XKtg@mail.gmail.com> (raw)
In-Reply-To: <CA+55aFx0b8ATmeO8KRaHrgsZnhT_0TqotsPUkxN4gbCsvrZuyA@mail.gmail.com>

On Sun, Sep 2, 2018 at 7:47 PM Linus Torvalds
<torvalds@linux-foundation.org> 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

  reply	other threads:[~2018-09-03  2:52 UTC|newest]

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-08-29 12:10 Access to non-RAM pages Juergen Gross
2018-08-31 21:18 ` Jiri Kosina
2018-09-01 10:47   ` Juergen Gross
2018-09-01 17:13     ` Al Viro
2018-09-01 21:48       ` Jiri Kosina
2018-09-01 17:27   ` Linus Torvalds
2018-09-01 18:06     ` Linus Torvalds
2018-09-03  0:48       ` Benjamin Herrenschmidt
2018-09-03  0:55         ` Benjamin Herrenschmidt
2018-09-03  1:38           ` Linus Torvalds
2018-09-03  1:42             ` Linus Torvalds
2018-09-03  2:00               ` Benjamin Herrenschmidt
2018-09-03  2:10                 ` Linus Torvalds
2018-09-03  2:25                   ` Benjamin Herrenschmidt
2018-09-03  2:47                     ` Linus Torvalds
2018-09-03  2:52                       ` Linus Torvalds [this message]
2018-09-03  3:44                         ` Benjamin Herrenschmidt
2018-09-03  5:08                   ` Juergen Gross
2018-09-03  6:05                   ` Jiri Kosina
2018-09-03 10:36                   ` Will Deacon
2018-09-03  1:44             ` Benjamin Herrenschmidt
2018-09-03  1:46             ` Benjamin Herrenschmidt

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