From: Dave Chinner <david@fromorbit.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Jens Axboe <axboe@kernel.dk>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>,
Al Viro <viro@zeniv.linux.org.uk>
Subject: Re: [PATCH 2/2] fs: expose LOOKUP_NONBLOCK through openat2() RESOLVE_NONBLOCK
Date: Fri, 11 Dec 2020 11:58:30 +1100 [thread overview]
Message-ID: <20201211005830.GD3913616@dread.disaster.area> (raw)
In-Reply-To: <CAHk-=wiee7xKitbX74NvjcKDHLiE21=SbO9_urWBnvm=nSZAFQ@mail.gmail.com>
On Thu, Dec 10, 2020 at 03:29:23PM -0800, Linus Torvalds wrote:
> On Thu, Dec 10, 2020 at 2:29 PM Dave Chinner <david@fromorbit.com> wrote:
> >
> > So, really, this isn't avoiding IO at all - it's avoiding the
> > possibility of running a lookup path that might blocking on
> > something.
>
> For pathname lookup, the only case that matters is the RCU lockless lookup.
>
> That cache hits basically 100% of the time except for the first
> lookup, or under memory pressure.
>
> And honestly, from a performance perspective, it's the lockless path
> lookup that matters most. By the time you have to go to the
> filesystem, take the directory locks etc, you've already lost.
>
> So we're never going to bother with some kind of "lockless lookup for
> actual filesystems", because it's only extra work for no actual gain.
>
> End result: LOOKUP_NONBLOCK is about not just avoiding IO, but about
> avoiding the filesystem and the inevitable locking that causes.
Umm, yes, that is _exactly_ what I just said. :/
Cheers,
Dave.
--
Dave Chinner
david@fromorbit.com
next prev parent reply other threads:[~2020-12-11 1:01 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-12-10 20:01 [PATCHSET 0/2] fs: Support for LOOKUP_NONBLOCK / RESOLVE_NONBLOCK Jens Axboe
2020-12-10 20:01 ` [PATCH 1/2] fs: add support for LOOKUP_NONBLOCK Jens Axboe
2020-12-10 20:53 ` Linus Torvalds
2020-12-10 21:06 ` Jens Axboe
2020-12-11 2:45 ` Al Viro
2020-12-11 16:05 ` Jens Axboe
2020-12-11 17:20 ` Al Viro
2020-12-11 17:35 ` Linus Torvalds
2020-12-11 18:50 ` Jens Axboe
2020-12-11 21:51 ` Al Viro
2020-12-11 23:47 ` Jens Axboe
2020-12-11 17:33 ` Matthew Wilcox
2020-12-11 18:55 ` Jens Axboe
2020-12-11 2:35 ` Al Viro
2020-12-11 15:57 ` Jens Axboe
2020-12-11 17:21 ` Linus Torvalds
2020-12-11 17:29 ` Al Viro
2020-12-11 17:38 ` Al Viro
2020-12-11 17:44 ` Linus Torvalds
2020-12-11 21:46 ` Jens Axboe
2020-12-10 20:01 ` [PATCH 2/2] fs: expose LOOKUP_NONBLOCK through openat2() RESOLVE_NONBLOCK Jens Axboe
2020-12-10 22:29 ` Dave Chinner
2020-12-10 23:12 ` Jens Axboe
2020-12-10 23:29 ` Linus Torvalds
2020-12-11 0:58 ` Dave Chinner [this message]
2020-12-11 1:01 ` Linus Torvalds
2020-12-11 3:45 ` Dave Chinner
2020-12-11 18:07 ` Linus Torvalds
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