From: Linus Torvalds <torvalds@linux-foundation.org>
To: Catalin Marinas <catalin.marinas@arm.com>
Cc: kvm-ppc@vger.kernel.org, Christoph Hellwig <hch@infradead.org>,
cluster-devel <cluster-devel@redhat.com>, Jan Kara <jack@suse.cz>,
Andreas Gruenbacher <agruenba@redhat.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Paul Mackerras <paulus@ozlabs.org>,
Alexander Viro <viro@zeniv.linux.org.uk>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>,
linux-btrfs <linux-btrfs@vger.kernel.org>,
ocfs2-devel@oss.oracle.com
Subject: Re: [Ocfs2-devel] [PATCH v8 00/17] gfs2: Fix mmap + page fault deadlocks
Date: Wed, 20 Oct 2021 20:19:40 -1000 [thread overview]
Message-ID: <CAHk-=wgP058PNY8eoWW=5uRMox-PuesDMrLsrCWPS+xXhzbQxQ@mail.gmail.com> (raw)
In-Reply-To: <YXCbv5gdfEEtAYo8@arm.com>
On Wed, Oct 20, 2021 at 12:44 PM Catalin Marinas
<catalin.marinas@arm.com> wrote:
>
> However, with MTE doing both get_user() every 16 bytes and
> gup can get pretty expensive.
So I really think that anything that is performance-critical had
better only do the "fault_in_write()" code path in the cold error path
where you took a page fault.
IOW, the loop structure should be
repeat:
take_locks();
pagefault_disable();
ret = do_things_with_locks();
pagefault_enable();
release_locks();
// Failure path?
if (unlikely(ret == -EFAULT)) {
if (fault_in_writable(..))
goto repeat;
return -EFAULT;
}
rather than have it be some kind of "first do fault_in_writable(),
then do the work" model.
So I wouldn't worry too much about the performance concerns. It simply
shouldn't be a common or hot path.
And yes, I've seen code that does that "fault_in_xyz()" before the
critical operation that cannot take page faults, and does it
unconditionally.
But then it isn't the "fault_in_xyz()" that should be blamed if it is
slow, but the caller that does things the wrong way around.
Linus
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next prev parent reply other threads:[~2021-10-21 6:20 UTC|newest]
Thread overview: 47+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-10-19 13:41 [Ocfs2-devel] [PATCH v8 00/17] gfs2: Fix mmap + page fault deadlocks Andreas Gruenbacher
2021-10-19 13:41 ` [Ocfs2-devel] [PATCH v8 01/17] iov_iter: Fix iov_iter_get_pages{, _alloc} page fault return value Andreas Gruenbacher
2021-10-19 13:41 ` [Ocfs2-devel] [PATCH v8 02/17] powerpc/kvm: Fix kvm_use_magic_page Andreas Gruenbacher
2021-10-19 13:41 ` [Ocfs2-devel] [PATCH v8 03/17] gup: Turn fault_in_pages_{readable, writeable} into fault_in_{readable, writeable} Andreas Gruenbacher
2021-10-19 13:41 ` [Ocfs2-devel] [PATCH v8 04/17] iov_iter: Turn iov_iter_fault_in_readable into fault_in_iov_iter_readable Andreas Gruenbacher
2021-10-19 13:41 ` [Ocfs2-devel] [PATCH v8 05/17] iov_iter: Introduce fault_in_iov_iter_writeable Andreas Gruenbacher
2021-10-20 16:25 ` Catalin Marinas
2021-10-19 13:41 ` [Ocfs2-devel] [PATCH v8 06/17] gfs2: Add wrapper for iomap_file_buffered_write Andreas Gruenbacher
2021-10-19 13:41 ` [Ocfs2-devel] [PATCH v8 07/17] gfs2: Clean up function may_grant Andreas Gruenbacher
2021-10-19 13:41 ` [Ocfs2-devel] [PATCH v8 08/17] gfs2: Introduce flag for glock holder auto-demotion Andreas Gruenbacher
2021-10-19 13:41 ` [Ocfs2-devel] [PATCH v8 09/17] gfs2: Move the inode glock locking to gfs2_file_buffered_write Andreas Gruenbacher
2021-10-19 13:41 ` [Ocfs2-devel] [PATCH v8 10/17] gfs2: Eliminate ip->i_gh Andreas Gruenbacher
2021-10-19 13:41 ` [Ocfs2-devel] [PATCH v8 11/17] gfs2: Fix mmap + page fault deadlocks for buffered I/O Andreas Gruenbacher
2021-10-19 13:41 ` [Ocfs2-devel] [PATCH v8 12/17] iomap: Fix iomap_dio_rw return value for user copies Andreas Gruenbacher
2021-10-19 13:42 ` [Ocfs2-devel] [PATCH v8 13/17] iomap: Support partial direct I/O on user copy failures Andreas Gruenbacher
2021-10-19 13:42 ` [Ocfs2-devel] [PATCH v8 14/17] iomap: Add done_before argument to iomap_dio_rw Andreas Gruenbacher
2021-10-19 15:51 ` Darrick J. Wong
2021-10-19 19:30 ` Andreas Gruenbacher
2021-10-20 1:57 ` Darrick J. Wong
2021-10-19 13:42 ` [Ocfs2-devel] [PATCH v8 15/17] gup: Introduce FOLL_NOFAULT flag to disable page faults Andreas Gruenbacher
2021-10-19 13:42 ` [Ocfs2-devel] [PATCH v8 16/17] iov_iter: Introduce nofault " Andreas Gruenbacher
2021-10-19 13:42 ` [Ocfs2-devel] [PATCH v8 17/17] gfs2: Fix mmap + page fault deadlocks for direct I/O Andreas Gruenbacher
2021-10-19 15:40 ` [Ocfs2-devel] [PATCH v8 00/17] gfs2: Fix mmap + page fault deadlocks Linus Torvalds
2021-10-19 16:00 ` Bob Peterson
2021-10-20 16:36 ` Catalin Marinas
2021-10-20 20:11 ` Linus Torvalds
2021-10-20 22:44 ` Catalin Marinas
2021-10-21 6:19 ` Linus Torvalds [this message]
2021-10-22 18:06 ` Catalin Marinas
2021-10-22 19:22 ` Linus Torvalds
2021-10-25 19:00 ` Andreas Gruenbacher
2021-10-26 18:24 ` Catalin Marinas
2021-10-26 18:50 ` Linus Torvalds
2021-10-26 19:18 ` Linus Torvalds
2021-10-27 19:13 ` Catalin Marinas
2021-10-27 21:14 ` Linus Torvalds
2021-10-28 21:20 ` Catalin Marinas
2021-10-28 21:40 ` Catalin Marinas
2021-10-28 22:15 ` Andreas Grünbacher
2021-10-29 12:50 ` Catalin Marinas
2021-10-28 22:32 ` Linus Torvalds
2021-10-29 17:50 ` Catalin Marinas
2021-10-29 18:47 ` Linus Torvalds
2021-10-25 18:24 ` Andreas Gruenbacher
2021-10-26 5:12 ` Theodore Ts'o
2021-10-26 9:44 ` Andreas Gruenbacher
2021-10-27 21:21 ` Andreas Gruenbacher
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