From: Al Viro <viro@zeniv.linux.org.uk>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andreas Gruenbacher <agruenba@redhat.com>,
cluster-devel <cluster-devel@redhat.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Jan Kara <jack@suse.cz>, Matthew Wilcox <willy@infradead.org>
Subject: Re: [RFC 5/9] iov_iter: Add iov_iter_fault_in_writeable()
Date: Sat, 12 Jun 2021 21:47:29 +0000 [thread overview]
Message-ID: <YMUrcUXS5jprfGPF@zeniv-ca.linux.org.uk> (raw)
In-Reply-To: <CAHk-=whcnziOWqVESWKJ6Y1_sG2S2AOa1vv5yKzUGs5gM7qYpQ@mail.gmail.com>
On Sat, Jun 12, 2021 at 02:33:31PM -0700, Linus Torvalds wrote:
> That said, reads are obviously much easier, and I'd probably prefer
> the model for writes to be to not necessarily pre-fault anything at
> all, but just write to user space with page faults disabled.
*nod*
I don't like that write pre-fault model at all - note that unlike read
we'll end up with atomic operations, etc. and there's a plenty of
non-obvious ways for that to end up being costly, even assuming it
works correctly in all cases.
O_DIRECT case is a PITA - there we use GUP and there's no way
to tell GUP that in the current situation we do *NOT* want to hit
->fault()/->page_mkwrite()/etc. pagefault_disable() won't be even
noticed there...
WARNING: multiple messages have this Message-ID (diff)
From: Al Viro <viro@zeniv.linux.org.uk>
To: cluster-devel.redhat.com
Subject: [Cluster-devel] [RFC 5/9] iov_iter: Add iov_iter_fault_in_writeable()
Date: Sat, 12 Jun 2021 21:47:29 +0000 [thread overview]
Message-ID: <YMUrcUXS5jprfGPF@zeniv-ca.linux.org.uk> (raw)
In-Reply-To: <CAHk-=whcnziOWqVESWKJ6Y1_sG2S2AOa1vv5yKzUGs5gM7qYpQ@mail.gmail.com>
On Sat, Jun 12, 2021 at 02:33:31PM -0700, Linus Torvalds wrote:
> That said, reads are obviously much easier, and I'd probably prefer
> the model for writes to be to not necessarily pre-fault anything at
> all, but just write to user space with page faults disabled.
*nod*
I don't like that write pre-fault model at all - note that unlike read
we'll end up with atomic operations, etc. and there's a plenty of
non-obvious ways for that to end up being costly, even assuming it
works correctly in all cases.
O_DIRECT case is a PITA - there we use GUP and there's no way
to tell GUP that in the current situation we do *NOT* want to hit
->fault()/->page_mkwrite()/etc. pagefault_disable() won't be even
noticed there...
next prev parent reply other threads:[~2021-06-12 21:48 UTC|newest]
Thread overview: 49+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-31 17:01 [RFC 0/9] gfs2: handle page faults during read and write Andreas Gruenbacher
2021-05-31 17:01 ` [Cluster-devel] " Andreas Gruenbacher
2021-05-31 17:01 ` [RFC 1/9] gfs2: Clean up the error handling in gfs2_page_mkwrite Andreas Gruenbacher
2021-05-31 17:01 ` [Cluster-devel] " Andreas Gruenbacher
2021-05-31 17:01 ` [RFC 2/9] gfs2: Add wrapper for iomap_file_buffered_write Andreas Gruenbacher
2021-05-31 17:01 ` [Cluster-devel] " Andreas Gruenbacher
2021-05-31 17:01 ` [RFC 3/9] gfs2: Add gfs2_holder_is_compatible helper Andreas Gruenbacher
2021-05-31 17:01 ` [Cluster-devel] " Andreas Gruenbacher
2021-05-31 17:01 ` [RFC 4/9] gfs2: Fix mmap + page fault deadlocks (part 1) Andreas Gruenbacher
2021-05-31 17:01 ` [Cluster-devel] " Andreas Gruenbacher
2021-06-01 6:00 ` Linus Torvalds
2021-06-01 6:00 ` [Cluster-devel] " Linus Torvalds
2021-06-02 11:16 ` Andreas Gruenbacher
2021-06-02 11:16 ` [Cluster-devel] " Andreas Gruenbacher
2021-06-11 16:25 ` Al Viro
2021-06-11 16:25 ` [Cluster-devel] " Al Viro
2021-06-12 21:05 ` Al Viro
2021-06-12 21:05 ` [Cluster-devel] " Al Viro
2021-06-12 21:35 ` Al Viro
2021-06-12 21:35 ` [Cluster-devel] " Al Viro
2021-06-13 8:44 ` Steven Whitehouse
2021-06-13 8:44 ` Steven Whitehouse
2021-05-31 17:01 ` [RFC 5/9] iov_iter: Add iov_iter_fault_in_writeable() Andreas Gruenbacher
2021-05-31 17:01 ` [Cluster-devel] " Andreas Gruenbacher
2021-05-31 17:12 ` Al Viro
2021-05-31 17:12 ` [Cluster-devel] " Al Viro
2021-06-12 21:12 ` Al Viro
2021-06-12 21:12 ` [Cluster-devel] " Al Viro
2021-06-12 21:33 ` Linus Torvalds
2021-06-12 21:33 ` [Cluster-devel] " Linus Torvalds
2021-06-12 21:47 ` Al Viro [this message]
2021-06-12 21:47 ` Al Viro
2021-06-12 23:17 ` Linus Torvalds
2021-06-12 23:17 ` [Cluster-devel] " Linus Torvalds
2021-06-12 23:38 ` Al Viro
2021-06-12 23:38 ` [Cluster-devel] " Al Viro
2021-05-31 17:01 ` [RFC 6/9] gfs2: Add wrappers for accessing journal_info Andreas Gruenbacher
2021-05-31 17:01 ` [Cluster-devel] " Andreas Gruenbacher
2021-05-31 17:01 ` [RFC 7/9] gfs2: Encode glock holding and retry flags in journal_info Andreas Gruenbacher
2021-05-31 17:01 ` [Cluster-devel] " Andreas Gruenbacher
2021-05-31 17:01 ` [RFC 8/9] gfs2: Add LM_FLAG_OUTER glock holder flag Andreas Gruenbacher
2021-05-31 17:01 ` [Cluster-devel] " Andreas Gruenbacher
2021-05-31 17:01 ` [RFC 9/9] gfs2: Fix mmap + page fault deadlocks (part 2) Andreas Gruenbacher
2021-05-31 17:01 ` [Cluster-devel] " Andreas Gruenbacher
2021-06-01 5:47 ` Linus Torvalds
2021-06-01 5:47 ` [Cluster-devel] " Linus Torvalds
2021-05-31 17:57 ` [Cluster-devel] [RFC 0/9] gfs2: handle page faults during read and write Linus Torvalds
2021-05-31 20:35 ` Andreas Gruenbacher
2021-05-31 20:35 ` [Cluster-devel] " Andreas Gruenbacher
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=YMUrcUXS5jprfGPF@zeniv-ca.linux.org.uk \
--to=viro@zeniv.linux.org.uk \
--cc=agruenba@redhat.com \
--cc=cluster-devel@redhat.com \
--cc=jack@suse.cz \
--cc=linux-kernel@vger.kernel.org \
--cc=torvalds@linux-foundation.org \
--cc=willy@infradead.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.